volcanic-ash-derived forest soils of the inland northwest

United StatesDepartmentof Agriculture

Forest Service

Rocky MountainResearch Station

ProceedingsRMRS-P-44

March 2007

Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration

9-10 November 2005 Coeur d’Alene, ID

Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 220 p.

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Abstract ________________________________________ Volcanic ash from the eruption of Mt. Mazama ~7,700 years ago has a strong influ-ence on many forested landscapes of the Pacific Northwest and Intermountain regions of the USA and Canada. Because of the unique biological, physical and chemical properties of the ash, it is closely tied to plant communities and forest productivity, and should therefore be considered as a resource to protect when harvesting, burning, or site preparation activities occur on it. How did this symposium get started? There has been a steady stream of questions, problems, and research on volcanic ash-cap soils for many decades. This symposium was designed to assemble experts to discuss our state-of-knowledge about volcanic ash-cap soil management and restoration. About 200 scientists and natural resource managers participated in this conference, which was held at the Coeur d’Alene Resort, Coeur d’Alene, ID in November 2005.

The Technical Committee __________________________Deborah S. Page-Dumroese is a Research Soil Scientist and Project Leader, Rocky Mountain Research Station. Debbie’s research has focused on long-term soil productivity after management activities, including belowground chemical, physical, and biological properties.

Richard E. Miller is a retired Research Soil Scientist from the Pacific Northwest Research Station. Dick is still actively involved in soil research and is currently working to address issues of soil quality and monitoring.

Jim Mital is the Forest Ecologist, Soil Scientist, and Weed Coordinator on the Clearwater National Forest. Jim has worked to help design “soil friendly” management options for resource managers.

Paul McDaniel is Professor of Soil Science in the College of Agricultural and Life Sci-ences at the University of Idaho. Paul’s research activities have included elucidating the unique chemical and physical properties of ash-cap soils.

Dan Miller is Silviculture Manager for Potlatch Forest Holdings, Inc., Lewiston, ID. Dan has been instrumental in working with logging contractors to reduce soil impacts during harvesting.

Contents______________________________________________________ Page

Properties, Characteristics, and Distribution of Ash-cap Soils .............................................. 1

Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for Management and Restoration ............................................................................... 3 Steven B. Daley-Laursen

Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils ............................. 7 Mark Kimsey, Brian Gardner, and Alan Busacca

Field Identification of Andic Soil Properties for Soils of North-central Idaho ................................ 23 Brian Gardner

Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests ...... 31 P. A. McDaniel and M. A. Wilson

Assessing Quality in Volcanic Ash Soils ....................................................................................... 47 Terry L. Craigg and Steven W. Howes

Past Activities and Their Consequences on Ash-cap Soils .................................................. 67

Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils ....................................... 69 Leonard R. Johnson, Debbie Page-Dumroese, and Han-Sup Han

Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils .......... 83 P. R. Robichaud, F. B. Pierson, and R. E. Brown

Management Alternatives for Ash-cap Soils ........................................................................... 95

Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends .................................................................................... 97 Mike Curran, Pat Green, and Doug Maynard

Restoring and Enhancing Productivity of Degraded Tephra-Derived Soils ................................ 121 Chuck Bulmer, Jim Archuleta, and Mike Curran

Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest......................................................................................................................... 137 Mariann T. Garrison-Johnston, Peter G. Mika, Dan L. Miller, Phil Cannon, and Leonard R. Johnson

Economics of Soil Disturbance ................................................................................................... 165 Han-Sup Han

Special Topic—Grand Fir Mosaic ........................................................................................... 173

The Grand Fir Mosaic Ecosystem—History and Management Impacts ..................................... 175

D. E. Ferguson, J. L. Johnson-Maynard, and P. A. McDaniel

Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils .................. 185 Deborah Page-Dumroese, Dennis Ferguson, Paul McDaniel, and Jodi Johnson-Maynard

Summaries of Poster Papers .................................................................................................. 203

WEPP FuME Analysis for a North Idaho Site ............................................................................. 205 William Elliot, Ina Sue Miller, and David Hall

Erosion Risks in Selected Watersheds for the 2005 School Fire Located Near Pomeroy, Washington on Predominately Ash-Cap Soils .............................................................211 William Elliot, Ina Sue Miller, and Brandon Glaza

Conference Wrap-up .................................................................................................................. 215 Richard E. Miller

Properties, Characteristics, and Distribution of Ash-cap Soils

Past Activities and Their Consequences on Ash-cap Soils

Management Alternatives for Ash-cap Soils

Special Topic— Grand Fir Mosaic

Summaries of Poster Papers

Properties, Characteristics, and Distribution of Ash-cap Soils

�USDA Forest Service Proceedings RMRS-P-44. 2007

Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for

Management and RestorationSteven B. Daley-Laursen

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Steven B. Daley-Laursen, Dean and Professor, College of Natural Resources, University of Idaho.

GoodMorningandWelcome.Mytasktodayis toset thestageforaproductiveconferencebyprovidinganhistoricalcontext,anoverviewofthesubjectmattertobecovered,andachallengefornextstepsbyinterestedscientistsandpractitioners.

An Historical Perspective

VolcanoeshavebeenpartoftheEarth’shistoryeversinceithashadasolidsurface.And,volca-noeshavebeenapartofhumancultureforthousandsofyears.Insomeways,ourreactionstothemagnitudeofavolcanicexplosionhaven’tevolvedasmuchasonemightthink.Rangingfromancientcultureswhobelievedthatvictimsshouldbesacrificedinresponsetovolcaniceruption,toHarryTrumanwhostubbornlysacrificedhimselfduringthemostrecenteruptioninthecontinentalUnitedStates,volcanoeshaveimpactedourlivesinmanywaysandwillcontinuetodosointhefuture. Butdisastersometimesbringsfortune.HereontheWestCoastwheresomevolcanoeseruptvio-lentlyevery20-30yearsorso,weliveinoneofthegrandestash-caplocationsintheworld.SoilsthroughouttheInlandNorthwestregionoftheUnitedStatesextendingfromtheCascadeMountainsofOregonandWashington toNorthern IdahoandWesternMontanahavebeen influencedandoverlainbytephrafromcataclysmiceruptionsofMountMazama. About6,850yearsagoMountMazama,astrato-volcano,collapsedtoproduceCraterLake,oneoftheworld’sbestknowncalderas.Thecalderaisabout6miles(10km)wide.Thecatastrophicpyro-clasticeruptionreleasedabout12cubicmiles(50cubickm)ofmagmatothesurface.Itwasoneofthelargesteruptionsinthelast10,000years. TheMazamaeruptionwasfollowedbytheMay18,1980eruptionofMountSt.Helensinwest-centralWashington.Thiseruptionspreadlessthan1/100thoftheMazamaashvolumeoverareasofeasternWashingtonandNorthernIdaho.TheSt.Helensashplumecarriedbythejetstreamtook2weekstocircletheglobe!ThoughconsiderablysmallerinvolumeoutputthantheMazamaerup-tion,theMountSt.Helenseruptionanddepositionhadeffectsonsoilsandproductivityinourregionthatarestillvisibleandproudlymeasurable.

4 USDA Forest Service Proceedings RMRS-P-44. 2007

Daley-Laursen Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for Management and Restoration

Onapersonalnote,thesevolcanoesandtheconsequenceoftheireruptionshavehadadirectimpactonmylifeandcareerinthreeways.AsanOregonianbybirthIwasavisitortoCraterLakelearningaboutlocalgeologyandforests.AsaresidentofMoscow,IdahoduringtheMay1980eruptionofSt.Helens(andthenearly1-yearaftermath)Ihadtheexperienceofbeingblanketedwithashandhavinglife’spaceslowtoawalkwithamaskandgogglesinasnowywhitehaze.And,asastudentoftheHabitatTypeatUIandaresearcherdevelopingstandgrowthsimulationmodelsintheGrandfir,Douglas-firandcedarhemlocksystemsoftheInlandNorthwest,Ilearnedfirsthandabouttheimpactofashonsoilpropertiesandchemistryandsiteproductivityandpotentialvegetation.So,Ihaveforsometimebeenawedbythepoweroftheseprofoundphenomena—thevolcanoesthatproducetheash,andtheashcapsthataddvaluetotheregion’ssoils.

My experiencewith the aftermathof volcanic eruptionwas expanded anddeepenedthispastyear,whenIhadtheopportunitytotourLasVallesCalderainnorthernNewMexico.Thisisa50milewidecalderathatblewitstop1.2millionyearsago,leavingbehindaninspiringlandscapeofbiologicaldiversity.IwenttheretomeetupwithscientistsfromthreeNewMexicouniversitiesconductingresearchonwatersheddynamicsandcarbon-waterrelations.Thisisaremarkableplaceat10,000feetintheSouthernRockyMountains.Don’tmissyouropportunitytovisitandlearnaboutthepastandpresentconditionsofLasVallesCaldera.

Thesemajorvolcaniceruptionsanddepositionsallcreatedthesamewondrousoutcome;ash-capsoils.Asaresultoffrequentvolcanicactivity,thesoilsoftheNorthwestareuniqueandbehavedifferentlythananywhereelseintheUnitedStates.Asyou’llhearfromadozenresearchersandlandmanagersoverthenext2days,wenowknowmuchabout thepropertiesandcharacteristicsof thesedepositedsoilsandtheeffectsofouractivityonthem.

An Overview of Our State of Knowledge— Preview of the Conference _______________________________________

Weknow thedistributionofAndic soils, andMarkwill tell youmore.WeknowaboutthechemicalandphysicalpropertiesofAndisols.Theyarelightandfluffy,lowdensityandhaveremarkablewater-holdingcapacity.Paulwilltellusmoreaboutallof this,drawing fromhis2005 treatiseonAndisols.WeknowsomethingaboutAndic soilqualityandwillhearmoreabout that fromStevelaterthisafternoon.

Weknowthatthemostsignificantglassaccumulationsarefoundinforestedareas.IthasbeensuggestedthatoutsideaforeststructureliketheDouglas-fir,orthemoremesicGrandfirandcedarhemlockecosystems,volcanicashisnotretainedagainsterosion,certainlynotunderextremeconditionsofmanagementthatexacerbateerosion.

WealsoknowthereisastronglinkbetweenAndisoldistributionandforestproductivity;referencemyearliercommentsabouthabitat typeasapredictorvariableinstandgrowthsimulationmodels.Inthe1970s,HabitatTypewasex-plainingmuchvariationinourtreegrowthandforeststandsimulationmodels,actingasaneffectiveintegratorofslope,aspect,elevation,moistureandtem-peratureinthepredictionofspeciesoccurrenceandabundanceaswellastreeandshrubgrowthrate.Atthattime,manyscientistsandmanagerswerebeginning

�USDA Forest Service Proceedings RMRS-P-44. 2007

Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for Management and Restoration Daley-Laursen

tobelievethattheonefactornotadequatelystratifiedinDaubenmire’sHabitatTypeschemewassoiltype.

Ash-capsoilsplayacriticalroleinwaterrelationsandnutritionalecology,andthus,plantdiversityinforestedecosystems.LaterattemptsathabitattypingintheUnitedStateshavetakensoiltypemuchmoreseriously.

Inmorerecentscienceonforestnutrition,soilparentmaterialhastakenoncelebritystatusasapredictorvariableinsiteproductivity.Researchersandlandmanagersnowspeakofgood and bad rocks(parentmaterial)andacknowledgethroughempiricalandlaboratorysciencethecharacteristicsofashsoilsandtheirdirectimpactonnutritionalecology.Throughcooperativeresearchandoutreach,thishashadadirectinfluenceonmanagementprescriptionsonbothpublicandprivateforestownerships.

From this body of research and practice, we know that properly managedAndicsoilscanbesomeofthemostproductiveonearth.DennisandLarrywillsharetheirknowledgeonmanagementregimesonforestedsystemswithash-capsoils.Mariannewillsharewaystoimprovetreeperformancethroughnutritionalaugmentationandsitedecisions.PetewilltellyouabouttheeffectsofdifferentfireregimesonAndicsoiltypes.

Weknowthesesoilsaresusceptibletocompaction,anddecreaseinvalueandvolumeunderintenseandfrequentfireanderosionfollowingirresponsibleforestman-agementpractices.HanandLeonardwillreviewtheeffectsofmachinetraffic,plansforalighterfootprintduringforestoperations,andtheoveralleconomicsoftimberoperationswithaneyetoecologicalandeconomicsustainability.Chuckwillintroduceustorestorationschemesfordegradedsoils.And,Mikewillsharebestmanagementpracticesrelatingtoinsectanddiseasepopulationsandharvestoperations.

The Challenge to Scientists and Practitioners— Where We Go From Here _________________________________________

Weknowmuch,andyou’vegatheredanimpressivecrewofscientistsandprac-titionerstosharethecurrentknowledgebase.But,theconferenceisaboutmorethanjustdumpingallthecurrentknowledgeonthetable.It’saboutsynthesizingcurrentknowledgeintoamorecoherentperspectiveonthesesoilsandtheman-agementtheycantolerate.And,justasimportant,it’saboutframingthenextsetofquestions…layingoutyourscienceroadmapforthefuture,anddoingittogether.

Ininterviewingsoilsfolksandmanagersinpreparationforthispresentation,IwastoldbymorethanonepersonthatmostofthestudiesonAndisolshaveoccurredintheMidwestandoverseas—inJapan,Iceland,andNewZealandforexample,andthatthebodyofinformationavailableintheU.S.isfleetingandincomplete.ItwouldbegoodtoorganizealistofhighestpriorityresearchtobeconductedonAndicsoilsinthisregion.

Mostalsoagreethataroundtheedgesofthisspottingsciencebase,therearementalvolumesofendemic,practitionerknowledgeaboutAndicsoilsstoredintheexpertsystemsthatareourexperiencedlocalforestmanagers.Itwouldbeusefultoallofyoutoorganizethisendemicknowledgeandsubjectittoscientificscrutiny,invalidationandconfirmation.That’swhyyou’rehere—tomatchtheinsightsandexperienceofforestmanagerswiththecuriosityofforestresearchers…todevelopa coherent research agenda that will lead to best practices for protection andsustainabilityofthisimportantAndicsoilresource.

� USDA Forest Service Proceedings RMRS-P-44. 2007

Daley-Laursen Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for Management and Restoration

That’s therealreasonIacceptedtheinvitationtobewithyoutoday.Obvi-ously,Ican’tstandtoetotoewithyouonthescienceofsoilsortheintricaciesandart-formofmanagement.But,Ihavespentmycareerstraddlingtheresearchandoutreachworldsofacademia,strivingtobringtheresearcherandpractitionertogetheraroundacoherentandintegratedscienceandmanagementagenda.Thebestoutcomesofscienceareachievedwhenthescientistandpractitionercon-ceptualizeaproblemandresearchquestiontogetherandI’mpassionateaboutmakingthistypeofconnectionareality.Therewardsareprofoundforallwhosubscribe.

So,myclosingstatementisanadmonitioninthatspiritofcollaborationandcoordination.

Soilsare taken forgrantedandunderratedby theaverageperson. Justdirt,youknow—uncorruptableandforeverstaticintheaveragemind’seye.But,youandIknowthisisn’ttrue.Theyareinfactthesubstrateonwhichmostlifeandbiodiversityresides,theyarethephysicalbaseonwhichthewatersystemself-regulates,theyareoftenthedefiningfactorinwhatyoucanandcannotdowellonaparticularsite.Andtheyarefragile,corruptibleanddegradable. Inmanycases,ifyouscrewthemuponce,youdon’tgetasecondchance.Inextremecasesoferodibility,whenthey’regone,they’regone.

TheAndicsoilisparticularlyerodible.StudiesofAndicsoilscangivecluestootherhighlyerodiblesoilsinevenmorecriticalregionsofbiodiversity,likethetopics.

Aswecontinuetogrowourunderstandingoftheworkingprocessesandfunc-tionsofecosystems,andasasociety,werecognizeandattempttoquantify,andeventrade,thevaluesofnaturalcapital,soilandit’srelationshiptowaterandcarbonwillbekeyareasofinquiry,value,creditandtrade.

MostclimatemodelersandcarbonscientistsnowagreethattheInlandNorth-west,infacttheGrandfirandcedarhemlockecosystemswithmoist,relativelywarmtemperatureregimesandatlowtomidelevations,maybeoneofNorthAmerica’sbiggestcarbonsponges.Andicsoilsdefinitelyplayaroleinthisequa-tion.Inthemarketplacethatcharacterizesoureconomyandsociety,ourvaluingofthesesoilswillfollowonourunderstandingofthesesoils.

ScientistsandmanagersinwesternNorthAmericahaveintheirbackyardalivinglaboratoryinwhichtostudytheAndicsoil.You’reinthedriver’sseatforadvancingtheworld’sknowledgeonthesesoils,theirpropertiesandcharacter-istics,theiradditionstoecologicalpotentialandproduction,andtheirresponsestotheregimesofhumanactivity.And,you’regatheredheretoponderthis.

So, listen well to what you and your colleagues know and chart a coursetogetherthatwillfillintheblanks.Identifythekeymanagementquestionsandissuesrelatingtoashcapsoils.Identifythecategoriesofinquirythatareimportanttopursue.Identifyareaswhereyouneedtogobeyondanecdotetoscienceandmakesomeplanstotestandinvalidateyourmentalmodels.Letthepractitionersinfluencetheresearchagenda,andholdthescientistsaccountableforgettingthescienceoutinusableformtomanagersontheground.

TheUniversityofIdahoisalandgrantinstitutionwithamissiontoadvancebothscienceandpracticeinnaturalresourcemanagement.Wewillbelookingforwaystopartnerinyournoblepursuit.

Goodluckwithyourmeetingandthanksagainfortheinvitationtoparticipate.

7USDA Forest Service Proceedings RMRS-P-44. 2007


Mark Kimsey is a Research Assistant, Department of Forest Resources, University of Idaho, Moscow, ID. Brian Gardner is a Soil Scientist, U.S. Department of Agriculture, Natural Resources Conservation Service, Moscow, ID. Alan Busacca is a Crop and Soil Scientist, Department of Crops and Soil Science, Washington State University, Pullman, WA.

Abstract Volcanic ash distribution and thickness were determined for a forested region of north-centralIdaho.Meanashthicknessandmultiplelinearregressionanalyseswereusedtomodeltheeffectofenvironmentalvariablesonashthickness.Slopeandslopecurvaturerelationshipswithvolcanicashthicknessvariedonalocalspatialscaleacrossthestudyarea.Ashdistributionandaspectshowedweakcorrelation.Elevationandecologicallybasedplantassociationsaccountedforabout54percentoftheobservedvariationinvolcanicashthickness.Climaxplantassociationsmoisterthangrandfir/queencupbeadlily(Abies grandis/Clintonia uniflora)hadconsistentlythickashmantlesandsoilsthatwouldbeclassifiedaseitherAndisolsorandicsubgroupsusingSoilTaxonomy.Thestatisticalmodelerrorof10.7cmwassignificantlylowerthanthe>20cmvariationoftenfoundinlocalsoilseries.Thismodelquantitativelyassessesashdistributionandcanbeintegratedintootherlocalecologicalmodels.

Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils

Mark Kimsey, Brian Gardner, and Alan Busacca

Introduction

VolcanicashfromeruptionsalongthePacificNorthwestCascadeRangehassignificantlyinfluenced forest soils of the Inland Northwest, U.S.A. (Mullineaux 1986; Shipley andSarna-Wojcicki1983).TheHoloceneeraeruptionofMt.Mazama(nowCraterLake,OR)distributed>116km3ofvolcanictephraacrossthisregion(Bacon1983;Zdanowiczandothers1999).SoilsinfluencedbythedepositionofMt.MazamatephracanbefoundthroughoutthewesternUnitedStatesandintosouthwesternCanada(fig.1).Soilsformedin,orinflu-encedbyvolcanicashare important to forestmanagement.Volcanicash-influencedsoilshave lower bulk density, higher porosity, and higher water infiltration and retention thansoilslessinfluencedorunaffectedbyash(McDanielandothers2005;Nanzyoandothers1993;Nimlos1980;WarkentinandMaeda1980).Amongthebenefitsofthesepropertiesisthereductionindroughtstressonplantcommunitiesduringextendedsummerdryperiods.

� USDA Forest Service Proceedings RMRS-P-44. 2007

Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils

RegionaldepositionfollowingtheeruptionofMt.Mazamawasestimatedatapproximately15-20cmthickineasternWashington,withthinninginareasmoredistal to theeruption(Busaccaandothers2001).Thecurrentdistributionpat-ternofvolcanicglassderivedfromtheMazamaeventismuchdifferentthanthisoriginaldepositionpattern.AmapdepictingtheprevalenceofvolcanicglassinmodernsurfacesoilsofEasternWashingtonindicatesonlyweaktephrainfluenceinsoilsofthesouthwestColumbiaPlateaueventhoughtheseareasareclosesttothevolcanicsourceofthetephra(fig.2)(Busaccaandothers2001).Instead,glasscontentofthesurfacesoilsincreaseswithincreasingdownwinddistancefromthesourcevolcano.Also,noneof themodern tephra-influencedsurfacesoilsarecomposedofpurevolcanicejecta.SoilsoftheBlueMountains,OR,andClearwaterMountains,ID,havesomeofthebest-expressedandicsoilproperties

Figure 1—Estimated spatial distribution of Mt. Mazama volcanic ash across the western United States and southwestern Canada. The study area for this research project is located within the boxed area of north-central Idaho (Mt. Mazama ash distribution adapted from Williams and Goles 19��).


Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils Kimsey, Gardner, and Busacca

intheregion,yetthesesoilsgenerallyhaveglasscontentsof20to50percentintheirsurfacelayers.

Severalmechanismshavebeenproposedasfactorsinthetransformationoftheoriginaltephrasheetintothemixeddistributionpatternsthatwesee.Theseinclude:1)apartialre-entrainmentofashbywindwithresultingredepositionfurtherdownwind(i.e.tothenortheast);2)burialofashmaterialbysubsequentepisodesofloessdeposition;3)bioturbationofthetephrabysoilfauna,whichservedtomixthevolcanicglassintothesurroundingsoilmass;and4)reducederosionlossandenhancedcaptureofremobilizedair-fallmaterialunderconiferousvegetationsuchasisfoundatthenorthernandeasternmarginsoftheColumbiaPlateau(Busaccaandothers2001;Hunter1988).

RecentNaturalResourceConservationService(NRCS)soilsurveyshaveex-tensivelymappedvolcanicash-influencedforestsoilsinportionsoftheInlandNorthwest. From these surveys, ash distribution and ecological/topographicrelationshipscanbeassessed.However,thesesoilsurveyrelationshipsareoftenpresented as a range in ash thickness. For example, volcanic ash thicknessesinHugusandBouldercreeksoilseriescommonlyfoundinourstudyareahavemappedvariations>20cm(SoilSurveyDivision2006).Asmoreinformationisgatheredontheroleofvolcanicashinforestproductivityandmanagement,for-estmanagersmayneedfinerresolutionofashdistributionthanarangeinashthickness.Theinherentvariationofsoilsurveysmaynotprovidethelevelofac-curacyneededfordecisionsupportsystems.Apotentiallyworkablealternativeisastatisticalre-analysisofindividualsoil-sitedescriptionscreatedduringlocalNRCSsoilsurveys.

Figure 2—Volcanic glass content of modern surface soils in eastern Washington (from Busacca and others 2001).



Basedontheaboverationale,ourobjectivewas toselectarelativelysmallgeographicregionwithintheInlandNorthwestforwhichextensivesoilandenvi-ronmentaldatawasavailableto1)developadatasetofvolcanicashdepths,habitattypes,andterrainfeatures;2)conductstatisticalanalysestoassessrelationshipsbetweenashthicknessandselectedvegetativeandtopographicfeatures;and3)determinetheprecisionandfitofastatisticalmodeltoestimatethethicknessofvolcanicashacrossalandscape.

Materials and Methods __________________________________________

Study Area

TheareachosenforthisstudyistheNRCSID-612soilsurveyregionofnorth-centralIdaho(fig.1).Thissurveyareaencompassesabout336,250haofdiverseclimaticfactors,habitattypes,andcomplexterrainattributes.Landscapesofthisregionaregenerallycharacterizedasmountainousinthenorthandeast,whilethesouthandwestarecharacterizedasbasaltplateaus/benchlandincisedwithdeepcanyons.Elevationrangesfrom300minthesouthwestto>1700minthenorthandeast.Meanannualprecipitation(MAP)roughlyfollowstheelevationalgradient,with<300mmMAPinthesouthwestand>1500mminthenortheast.Ponderosapine(Pinus ponderosa)andDouglas-fir (Pseudotsuga menziesiivar.glauca)habitattypesdominatethesouthernregionsofthesoilsurvey.Westernredcedar(Thuja plicata)andwesternhemlock(Tsuga heterophylla)dominatethewarm,moistuplandregions;withSubalpinefir(Abies lasiocarpa)andmountainhemlock(Tsuga mertensiana)predominantinthecolder,higherelevations(Cooperandothers1991).

Data Analysis

Ninehundredandtwenty-onesoil-sitedescriptionsandtheirXYcoordinateswereobtainedfromtheOrofino,ID,NRCSfieldoffice.Fieldrecordscomposedofvolcanicashthickness,terrainattribute,andhabitattypeobservationswereenteredintoadatabase.Theeffectivenumberofobservationsavailableforanalysesvariedsinceitwasnotunusualforcertainfieldobservationstonotberecordedonthefieldform.Asummaryofthefielddescriptorsandtheirpotentialinfluenceonvolcanicashdistributionispresentedintable1.

Thecontinuousvariableselevation(ELE),slope(SLP),andaspect(ASP)weregroupedintodiscreteclassestofacilitatethecomparisonofincrementalchangesinashthicknesswithterrainattributes.ELEwasclassedinto200-mintervals,SLPat10percentbreaks,andASPin45-degreequadrants.CurvaturevalueswerederivedfromaUnitedStatesGeologicalSurvey(USGS)30-mdigitalelevationmodel(DEM)usinggridalgebrainageographicinformationsystem(GIS).Thenumericalcurvaturevalueswere thengrouped into their respective linear (L),concave(C),andconvex(C)classes.

Averageashthicknessbyclasswascomputedforeachofthevariablesdescribedabove.Standarderrorswerecomputedandt-testsperformedtotestforsignificantdifferencesinashthicknessusinganα-levelof0.1.Variablesthatshowedsignifi-cantclassdifferencesinvolcanicashthicknessweresubsequentlytestedforuseaspredictorvariablesinavolcanicashdistributionmodel.Astepwisevariable



Table 1—Selected ecological and topographic features used in this study and their potential significance in determining volcanic ash distribution patterns (Cooper and others, 1991; Gallant, 2000).

Ecological/Topographic Features SignificanceElevation (meters): ELE Climate, vegetation type, potential energy 200-400 400-�00 �00-�00 �00-1000 1000-1200 1200-1400 1400+

Slope (%): SLP Overland and subsurface flow, velocity, and runoff 0-10 10-20 20-�0 �0-40 40-�0 �0-�0 �0+

Aspect (°): ASP Solar irradiation, wind erosion/deposition Flat N (�42.�-27.�) NE (27.�-72.�) E (72.�-117.�) SE (117.�-1�2.�) S (1�2.�-207.�) SW (207.�-2�2.�) W (272.�-297.�) NW (297.�-�42.�)

Up/Across Slope Curvature: PRCU/PLCU Flow acceleration, erosion/deposition rate, converging/diverging Linear flow, soil water content Concave Convex

Plant Associations: Climate, topography, site productivity, disturbance Vegetation Series: VS Pinus ponderosa (PIPO) Pseudotsuga menziesii (PSME) Abies grandis (ABGR) Thuja plicata (THPL) Tsuga heterophylla (TSHE) Tsuga mertensiana (TSME) Abies lasiocarpa (ABLA) Habitat Type: HT Festuca idahoensis (FEID) Physocarpus malvaceus (PHMA) Symphoricarpus albus (SYAL) Linnaea borealis (LIBO) Clintonia uniflora (CLUN) Asarum caudatum (ASCA) Adiantum pedatum (ADPE) Gymnocarpium dryopteris (GYDR)



selectionprocedurewasusedwithintheframeworkofagenerallinearmodel(GLM)toassesswhichvariablesexplainedthegreatestvariationinvolcanicashthickness.Variablesthatwerewithintheupper0.1percentileofaTypeIIIsums-of-squaresF-distributionwereretainedwithinthemodel.Thepredictionequationwasdeemedreliableifitproducedahighcoefficientofdetermination(R2)andlowrootmeansquareerror(RMSE).

Results _________________________________________________________

Topographic and Vegetative Indicators

VolcanicashishighlycorrelatedwithELE(fig.2).Each200-mincrementissignificantlydifferentupto1200m(p<0.1).Above1200m,thereisnosignificantdifferenceinmeanashthickness.Forestsoilsbelow600minelevationhaveashthicknesses≤10cm.Manylowelevationsoilsexhibitsignificantmixingof theshallowashmantlewithunderlyingsoilmaterial.These lowerelevation forestsoilsareclassifiedasvitrandicsubgroupsofasoilorder(SoilSurveyStaff1999).Forestsoils locatedatelevationsbetween600mand1200mhavemeanashthicknesses24to35cm.Thesesoilsareclassifiedasandicsubgroups.Volcanicashmantleshaveameanthicknessofabout45cmabove1200melevation.Ashmantlesdeeperthan36cmthatmeetseveralotherNRCScriteriaareconsideredmembersoftheorderAndisols(SoilSurveyStaff1999)orAndosolsoftheWorldReferenceBase(FAO/ISRIC/ISSS1998).

Meanashthicknessshowednosignificantdecreasewithincreasingslopegradient(fig.3).Meanashthicknessshowedrelativelylittlevariationwithasmallrangeof25to34cmacrossallslopeclasses.Slopes<10percentshowedsignificantlylessvolcanicashthanallclassesexceptthe60percentclass.Ashdepthincreasesup

Figure 3—Mean volcanic ash thickness as a function of elevation (ELE) class. Y-axis bars represent standard errors, with letters indicating significant differences (p < 0.1).

1�USDA Forest Service Proceedings RMRS-P-44. 2007


tothe20to30percentSLPclass;afterwhich,therearenosignificantdifferencesinashthicknessbySLPclass.The20to30percentclasshadsignificantlygreaterashdepthsthanallslopeclassesandwasmarginallygreaterthanthe40to50percentclass(p=0.12).

Northaspectsgenerallyexhibitthickerashmantlesthansouthfacingaspects(fig.4).N,NW,andSEaspectsshowmeanashdepths>32cm.NEandWfacingaspectshavethinnerashcaps(~30cm),butarenotsignificantlydifferentthanN,NW,orSEaspects.S,SW,andEaspectshavesignificantlythinnerashmantlesofabout27cm.

Figure 4—Mean volcanic ash thickness as a function of slope (SLP) class. Y-axis bars represent standard errors, with letters indicating significant differences (p < 0.1).

Slope curvature shows that nonlinear surfaces retain a greater thickness ofvolcanicashcomparedtolinearsurfaces(fig.5).Concaveandconvexsurfacesshowmeanashdepths>30cmforbothupslope(PRCU)andacrossslope(PLCU)surfacecurvature.LinearsurfacesinbothPRCUandPLCUaresignificantlylower(<25cm)thaneitherconvexorconcavesurfaces.Therewasnostatisticaldiffer-encebetweenconcaveandconvexineitherPRCUorPLCUslopecurvature.

Vegetationseriesandhabitattypeplantassociationsshowedthestrongestrela-tionshipwithvolcanicashthickness(fig.6).Overall,theponderosapine(PIPO)andDouglas-fir (PSME)vegetation serieshavevery thinvolcanicashmantles(<3cm)andshownosignificantchangebyhabitattypewithinseries.Grandfir(Abies grandis–ABGR)hasthewidestrangeinash-influenceofallvegetationseries.Meanashthicknessrangesfrom0to40cmdependingontheunderlyinghabitattypewithinseries.Themoisttwinflower(Linnaea borealis–LIBO)habitat



Figure 5—Mean volcanic ash thickness as a function of aspect (ASP) class. Y-axis bars represent standard errors, with letters indicating significant differences (p < 0.1).

Figure 6—Mean volcanic ash thickness as a function of upslope curvature (PRCU) class. Y-axis bars represent standard errors, with letters indicating significant differences (p < 0.1).



typeoftheABGRvegetationseriessurprisinglyshowsnosignificantashmantle(mean=0cm).AshthicknessinABGRhabitattypescanbedescribedasafunc-tionofincreasinglymoistunderstoryindicatorspecies,withtheexceptionofLIBO.HabitattyperankingsforvolcanicashthicknesswouldbeLIBO<PHMA/SYAL < CLUN < ASCA,wherePHMA,SYAL,CLUN,andASCA representninebark(Physocarpus malvaceus),snowberry(Symphoricarpus albus),queen-cupbeadlily(Clintonia uniflora),andwildginger(Asarum caudatum),respectively.Theserank-ingssuggestthatvitrandicintergradeswouldbemoreprevalentonPHMA/SYALandLIBOhabitattypes,andicintergradesonCLUN,andAndisolsonASCA.

Changing fromanABGR toawestern redcedar (THPL)vegetation series isaccompaniedbya5-cmincreaseinmeanashthicknesswhencomparingacrossCLUNhabitattypes.ThisshiftisnotevidentfortheASCAhabitattype,whichshows no significant differences between ABGR and THPL vegetation series.Maidenhair fern (Adiantum pedatum – ADPE) and oak-fern (Gymnocarpium dryopteris–GYDR)habitattypesshowareductionof>7cminmeanashthicknessoverABGR/THPL-ASCA.MeanashthicknessforCLUNandADPE/GYDRhabitattypessuggestthatandicintergradeswouldbemostcommon,withAndisols(inotherwords,ashmantle>36cm)occurringprimarilyunderanASCAhabitattype.Basedontheseobservations,understoryrankingsofhabitattypebyincreasingashthicknesswouldbeCLUN=ADPE/GYDR<ASCA.

Thewesternhemlock(TSHE)seriesdisplayedthelargestdifferenceinvolcanicash thickness between CLUN and ASCA habitat types (about 28 cm). TSHE-CLUNhabitattypesshowatleasta6-cmdecreaseinmeanashthicknesswhencomparedtoTHPL-CLUN;however,aTSHE-CLUNhabitattypewouldstillfallwithin the andic intergrade classification associated with other CLUN habitattypes.AshthicknessintheASCAhabitattypeissignificantlygreaterforTSHEvegetationseries than foranyother serieswithobservedASCAhabitat types.MeanashdepthsonTSHE-ASCAare54cm,whichwouldplacethemwellwithintheAndisolsoilorder.

Mountainhemlock(TSME)andsubalpinefir(ABLA)seriesaretypicallyfoundathigherelevationswhereairtemperaturesarerelativelylowandannualprecipitationhigh.Thewarmer,moisterASCAhabitatwasnotobserved.MeanashthicknessisgreateronTSME-CLUNthanABLA-CLUN,butthedifferenceisinsignificant.Volcanicash-thicknessonthesevegetationseriesis>36cm,thusplacingthemintotheAndisolorder.

Volcanic Ash Distribution Modeling

Theclassvariableslistedintable1wereaddedstepwiseintoamultiplelinearregressionequation.Variableswereassumedtobe independentandnormallydistributed.The finalmodel,withselectedvariablesactingas fixedeffectsonvolcanicashthickness,is:

ATjklmno=μ+PRCUj +ASPk+SLPl +ELEm+VS*HTn+εjklmno

where,

ATjklmnoisthepredictedvalueforobservationowithvegetationseries*habitat typeinteractionn atelevationmonslopelwithaspectkandupslope curvaturej,

1� USDA Forest Service Proceedings RMRS-P-44. 2007


μisoverallvolcanicashthicknessmean,PRCUjisthefixedeffectofupslopecurvature(concave,convex,orlinear),ASPkisthefixedeffectofaspect(N,NE,E,SE,S,SW,W,NW,orFLAT),SLPlisthefixedeffectofpercentslope(0-10,10-20,20-30,30-40,40-50, 50-60,or60+),ELEmisthefixedeffectofelevationinmeters(200-400,400-600,600-800, 800-1000,1000-1200,1200-1400,1400+),VS*HTnisthefixedeffectofvegetationseries*habitatinteraction(where,VSare ponderosapine,Douglas-fir,grandfir,westernredcedar,westernhemlock, mountainhemlock,orsubalpinefir;andHTareIdahofescue,ninebark/ snowberry,twinflower,queen-cupbeadlily,wildginger,ormaidenhairfern/ oak-fern),εjklmnoistheerrorterm;

where,j=3forupslopecurvature,k=9foraspect,l=7forslope,m=7forelevation,n=13 for vegetation series*habitat type interaction, ando=1 fornumberofobservationsperlocation.

Allclassvariables,exceptPLCU,explainedasignificantportionofvariationinvolcanicashthickness(p<0.1)(table2).VariablesrankedfromleasttomostinvarianceexplainedarePRCU<ASP<SLP<ELE<VS*HT.Theinteractionterm,VS*HT,accountedforthelargestpercentageofexplainedvarianceat71.2percent.ELEwasthesecondlargestat18.2percent.SLPandASPaccountedfor8.9percentcombined,andPRCUexplainedtheleastat1.7percent.Theoverallmodelwassignificant(p <0.001)andaccountedfor60percentoftheobservedvariationinashthickness.AmodelRMSEof10.7cmandCVof36percentindicatethatthereisasignificantamountofvariationstillunaccountedfor;however,thepredictiveerrorissignificantlylowerthanthevariationfoundinlocalsoilseries.

Table 2—General linear model variables retained in an ash prediction analysis. Partial variance indicates the percent of the model R2 explained by each retained variable.

Upslope Vegetation Series* Elevation Slope Aspect Curvature Habitat Type

Partial Variance (%) 1�.2 4.7 4.2 1.7 71.2Significancea <0.0001 0.00� 0.04 0.0� <0.0001aSignificance level tested at α = 0.1.

Discussion ______________________________________________________

Ecological and Topographic Indicators

Itisevidentfromthebroadrelationshipspresentedthatvolcanicashdistribu-tionisstronglyassociatedwithvegetationpatternsandlessdependentonterrainattributes.Elevation,althougha topographic feature, shows strongcollinearitywith localprecipitationgradientsandvegetativecover (datanot shown).Thissituationsuggeststhatelevationserveslocallyasaproxyvariableforinteractionsbetweenprecipitationandvegetationpatternsandtheirsubsequenteffectonashdistribution.



Slopeclassdidnothaveanegativeimpactonmeanashthicknesswithslopes>60percentshowingnosignificantdeclineinashdepths(fig.3).Thisresultsup-portsotherresearchonslopestabilityofvolcanicash.Inareviewofvolcanicashsoils,WarkentinandMaeda(1980)notethatvolcanicashonfree-standingslopesupto70degreesarecommoninregionsofhighrainfall.Theyattributethishighdegreeofstabilitytotheuniquepermeabilityofvolcanicash.

Thesignificantlylowermeanashthicknessinthe0-to-10percentslopeclassmaybeduetothegeographiclocationoftheseobservations.Amajorityoftheseobservations for nearly flat terrain were on the benchlands of the south andsouthwestportionofthestudyarea.ThisregionischaracterizedbylowelevationPSMEandABGRvegetationseries,whichoftenexhibitthinormixedvolcanicashmantles.

Theprevalenceofthickerashmantlesonnorthaspectsmaybeattributabletoseveralfactors(fig.4).Northaspectstypicallysupportmoisterplantcommunitiesinourstudyarea(Cooperandothers1991).Thesemoistplantcommunitiesmayprovidegreatersoilsurfacecover,whichwoulddecreasetheimpactofprecipitationandoverlandwaterflowonvolcanicashredistribution.Additionally,themoistureretainedwithinthesoilsafterprecipitationeventswouldbelesssusceptibletoevaporationfromsolarradiation.GiestandStrickler(1978)foundvolcanicashsoilsofOregontobesusceptibletowinderosiononceinadrystate.Assumingthatcurrentsouthwesterlyprevailingwindpatternsweresimilartohistoricpost-eruptionpatterns,dryvolcanicashonsouth-facingslopeswouldbeexpectedtobemoresusceptibletoredistributionbywindthannorthaspects.Thesignificantincrease inash thicknessonsoutheastslopes isanomalous to this theoryandsuggeststhattheoveralleffectofaspectonashdistributionislocalandintricatelytiedwithsurroundingtopographicandenvironmentalfactors.

Thesignificantdecreaseinashthicknessonlinearsurfacesshowninfigure5ispartiallycorrelatedwiththeslopeclasstheseobservationsshare.Areviewofthedatasetshowsthatabout67percentofthelinearsurfacesoccuronslopes<10percentwiththeremainderunevenlydividedamongseveralsteeperslopeclasses.Asdetailedinthepreviousdiscussionofslopeclasses,observationswithgradients<10percentarefoundprimarilyinthedrierbenchlandportionsofthestudyarea.Thecorrelationbetweenslopesteepnessandslopesurfacecurvaturewithinthedatasetmaymasklocaleffectsofslopecurvatureonashthickness.Surprisingly,convexsurfacesinbothupslopeandacrossslopepositionsdisplayednosignificantdecreaseinmeanashthicknessoverconcavesurfaces.Otherre-searchonvolcanicashdepositionaftertheeruptionofMt.St.Helenshasshownthatconcavesurfacessupportthickerashmantlesthanconvex(ZobelandAntos1991).Ourconflictingresultsmaybeduetothelevelofvariationfoundwithintheseclasses.Standarderrorsweresmallbecauseoflargesamplesizes,butthestandarddeviationswereoftenlargewithinthesurfaceclasses,reflectingsignifi-cantvariationwithinthedata.

Cooperandothers(1991)associateshiftsinclimaxplantassociationstodis-tinctive soil and/or topographicmicroclimate features.Habitat type shifts anddiffering soilashdepthareevidentacross thebroadhabitat typeassociationsobservedinourstudyarea(fig.7).Thesestrongrelationshipsmaybeattributedtomanycombinationsof topographic,climatic,oredaphic factors.Steeleandothers(1981)notedthattheinfluenceofvolcanicashcontributedtodistinctshiftsinIdahoplantcommunities.However,itisstillanopenquestionastowhether



thepresenceofvolcanicashisresponsibleforshiftsinplantassociations,orthatvariations in plant community were responsible for differential ash retention.Despite thisuncertainty,volcanicash thickness ishighlycorrelatedwithplantassociationsandcanbeusedtoassessashdistributionpatterns.

PSMEandPIPOvegetationseriesshowtheleastashthicknesswithinourdata.Shiftstomoisterhabitattypeswithinthesevegetationseriesshownosignificantdependenceonvolcanicash.Ithasbeensuggestedthatthesevegetationseriesnowresideonlandscapesthat,post-Mazamaeruption,weredrieranddidnotsupportforestvegetationcover.Lackofoverstorycoveranddryclimaticcondi-tionspreventedtheselandscapesfromretainingvolcanicashmantlessubsequenttotheeruption.

VolcanicashthicknessinABGRcommunitiesishighlyvariable.Unlikesuc-cessivelymoisterplantassociations,anABGRvegetationseriesdoesnotalwaysindicate the presence of significant volcanic ash influence. This variability ispartlyattributabletothetransitionzonethatABGRinhabitsbetweenxericandudicsoilmoistureregimes.Nearthedryendofthespectrum,ABGRplantcom-munitieswouldbeassociatedwithminimal tonoashinfluence.Thissuggeststhatanincreaseinplantavailablesoilmoisturewouldshifttheunderstoryplantcommunitytowardsmoisterhabitattypes.Thus,drierhabitattypes(PHMA/SYAL)oftenexhibitlessashinfluenceinthesoilthantheCLUNandASCAtypes.

AnexceptiontothispatternistheABGR-LIBOassociation.LIBOisconsideredtoinhabitmoisterenvironmentsthanPHMA,suggestingthatvolcanicashmightbepresenton thishabitat type.TheabsenceofvolcanicashonLIBOhabitattypesmaybeattributabletothefactthatonlyfiveobservationswerecollected

Figure 7—Mean volcanic ash thickness as a function of overstory (VS) and understory (HT) indicator plant species. Y-axis bars represent standard errors, with letters indicating significant differences (p < 0.1) (Cooper and others 1991).



withinthishabitattype,providingforapoorrepresentationoftherangeinashthickness.

All remaining plant associations moister than ABGR show significant ashinfluenceinthesoil.Thepresenceofathickashmantleisoftenidentifiedbythepresenceoftheseclimaxspecies.IncreasingashthicknessinthesoilisevidentinthehabitattypegradientswithintheTHPLseries;however,habitattypedif-ferencesareminimal.

TheTSHEvegetationseriesoccupiesanarrowecologicalrangeinnorthIdahoforestsandprimarilyinhabitsmoist,moderatetemperaturesitesandareintoler-anttodrought,excessmoisture,andfrost(Cooperandothers1991).Thenarrowecologicalrangesuggests thatotheredaphicandclimatic factorsmightplayalargerroleinTSHEdistributionthanvolcanicashinfluenceinthesoil.SuchfactorsmayalsoexplainwhyTSHE-CLUNplantassociationshavethinnerashmantlesthanTHPL-CLUN.TSHE-ASCAsitesdoshowsignificantincreasesinvolcanicashthickness.ThisresultsuggeststhatvolcanicashisassociatedwithashifttomoisterunderstoryplantcommunitieswithintheTSHEvegetationseries.

TSMEandABLAplantcommunitiesoccupyhighelevation siteswithup to1500mmofannualprecipitationwithinourstudyarea.Vegetationserieswithinthesezonesareprobablynotdependentonthepresenceofvolcanicashfortheirestablishment.Thehighprecipitationanddensevegetativecoveroftheseplantcommunitiesretainedvolcanicashsubsequenttooriginalashdeposition.

Volcanic Ash Distribution Modeling

Thestrengthoftherelationshipsbetweenelevation,plantcommunities,andvolcanicashproducesastrongpredictiveabilityforourashdistributionmodel.AnR2valueof0.6isconsideredanexcellentimprovementoverthelimitedre-gionalvolcanicashmodelingattempts(NimlosandZuuring1982).Predictionsfromthismodelallowquantitativeashassessmentswithaknownerrorwithinthestudyarea.Forestmanagerscanusethismodeltointegratethepredictionsintoageographicinformationsystem(GIS).Onemotivationbehinddevelopinga quantitative ash distribution model was to overcome the variation inherentwithinmappingunitsgeneratedthroughasoilsurvey.VolcanicashthicknessesinHugusandBouldercreeksoilseriescommonlyfoundinourstudyareahavemappedvariations>20cm(SoilSurveyDivision2006).Thepredictivemodel’sRMSEof10.7cmsignificantlyimprovesonthislevelofvariation,thusprovidingafinerresolutionsupporttoolforlocalforestsoilmanagement.

Furtherresearchshouldbeconductedtodeterminelocalaffectsoftopographicfeaturesonashdistributiondespitethesignificantimprovementthismodelpro-videsinpredictingashdepthanddistribution.Globalstatisticalproceduressuchasmultiplelinearregressionmaymasklocaltopographicinfluence.Adjustingastatisticalmodeltoperformamorelocalanalysismayyieldimprovedresults.Amorecostly,butperhapsinformativemethod,wouldbeadetailedsurveyofafinitelandscape.Researchatlocallevelsmayrevealtopographicandvolcanicashrelationshipsotherwisemaskedbylargeconventionalsoilsurveys.Regard-lessofwhichapproachisused,modelingashdistributionseemstobeinherentlyalocalexercise.Theextrapolationofmodelresultsoutsideastudyareaisnotrecommended.Theconceptsbehindthemodelpresentedinthispapermaybeapplicableelsewhere,buttherelationshipsasreflectedinthemodelparameterestimatesareunique.



Summary ______________________________________________________Thisstudy’sfindingssuggestthatvolcanicashdistributionisintricatelylinked

withelevationandplantcommunityassociations.Elevationincreasesprecipita-tion,whichinturnsupportsdifferentclimaxplantcommunities.Increasingplantdensityateachsuccessiveclimaxcommunitymayservetoretainashdepositssubsequenttovolcaniceruptionsandentrapwind-transportedvolcanicashfromdrier, lowerelevationsites.Topographicvariables showrelatively little impactonashthicknesspatterns.Severaloftheterrainattributesshowedclusteringbygeographiclocationwithinourstudyarea.Gentlerslopes,whichwerepredomi-natelyfoundatdrier,lowerelevations,supportedthinnerashmantles.Theslopecurvaturevariablewasalsolinkedtogeographiclocation.Nonlinearslopesweremostoftenfoundinthemountainousregionofthestudyarea.Thestrongeffectofelevationandvegetationhabitattypeseriesreducedtheabilitytodistinguishmeanashthicknessdifferencesbetweenconvexandconcavesurfaces.

Statisticalmodelingaccountedfor60percentoftheobservedvariationinashthicknessandreturnedanRMSEof10.7cm.Thesemodelstatisticsindicateasignificantdevelopment in thepredictioncapabilityofvolcanicash thickness.Modelerrorissignificantlylowerthanthevariationof>20cmoftenobservedinlocalash-influencedsoilseries.However,itbecameevidentduringouranalysesthatashdistributionandthicknessisheavilyinfluencedbylocalecologicalandtopographic attributes that cannot be assumed to affect ash depth uniformlyacrossastudyarea.Futureashmodelingeffortsmustfocusonassessinglocalenvironmental influences and account for nonstationarity in the independentvariables.Suchananalysismayclarifytheecologicalandtopographiceffectsonashdistributionandthicknessthatareotherwisegeneralizedinaglobalregres-sionanalysis.

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Brian Gardner: U.S. Department of Agriculture, Moscow, Idaho.

Field Identification of Andic Soil Properties for Soils of North-central Idaho

Brian Gardner

Introduction

Currently,laboratorymeasurementsaredefinitiveforidentifyingandicsoilpropertiesinboththeUSDASoilTaxonomy(SoilSurveyStaff1999)andtheWorldReferenceBaseforSoilResources(FAO/ISRIC/ISSS1998).Andicsoilproperties,asdescribedinSoilTaxonomy,resultmainlyfromthepresenceofsignificantamountsofallophone,imogolite,ferrihydriteoralumi-num-humuscomplexesinsoils.Therequiredpropertiesarehighacid-oxalateextractablealumi-numandironpercentages,lowbulkdensity,andhighphosphateretention.Inaddition,glassisacommoncomponentofandicsoilsoftheInlandNorthwestregion(McDanielandothers2005). A large body of work has been devoted to characterizing ash soils for classificationandmanagementpurposes.SummariesofthisworkincludeShojiandothers(1993)andDahlgrenandothers(2004).Howevernoneoftheseeffortshaveaddressedtheproblemofidentifyingsoilswithandicsoilpropertiesdirectlyinthefield.Mostsoilmappingpro-fessionals working with ashy materials are able to identify andic properties under fieldconditions. However, there is currently no summary of the methods used by individu-als to accomplish this identification. A procedure for recognizing andic materials usingfieldcharacteristicswouldassistboth those lackingexperiencewith thesematerialsandthose assessing soils from written descriptions. Also, a logically derived set of selec-tion criteria for detecting andic properties could help even experienced professionalsinareaswherevolcanicash influencehasbeendilutedbymixingwithothermaterials.


Gardner Field Identification of Andic Soil Properties for Soils of North-central Idaho

Thispaperwillexaminetwoalternativesfordetectingandicsoilproperties.Thefirstisthedevelopmentofanempiricalmodelusingroutinelyobservedsoilfeaturesasrecordedinsoildescriptionsfromnorth-centralIdaho.Thesecondistheuseofsodium-fluoride(NaF)pHtodetectthepresenceofallophaneorsimilaramorphousmaterialsinsoils.Theobjectivesofthisprojectwereto:1)identifyasetoffield-observablecharacteristicsthatcanreliablyidentifysoilsderivedfromMountMazamatephra;2)developasimplemodelusingthesecharacteristicstoevaluatesamplesastowhethertheymeetandiccriteriaornot;and,3)evaluateuseofNaF-pHinthisregionasatestforrecognizingashinfluence.

Methods and Materials __________________________________________Asetof323NaturalResourcesConservationService(NRCS)pedondescriptions

(or945separatesoilhorizons)fromLatahCounty,Idahowasusedtoevaluatehowwellasetoffieldobservationsallowsanobservertodistinguishandicmaterialsfromothersoilmaterials.Onlyhorizonshavingacompletesetofobservationsforallpropertiesandoccurringwithin50cmofthesoilsurfacewereused.Eachhorizonhadbeendesignatedasashyornon-ashyaccordingtotheexpertopinionoftheNRCSsoilscientistrecordingthesoildescription.Thedatasetcontains468horizonsdesignatedasashyand477horizonsdesignatednon-ashy.

The set of field observable characteristics proposed for recognizing andicmaterialsaresoilcolor(dryandmoist),structure,consistence(consistenceisthesetofstickiness,plasticity,ruptureresistancedryandruptureresistancemoist),and root abundance. Soil color isdescribedusing standardMunsellnotation.Structure,consistenceandrootabundancearedescribedusingthemethodsandnomenclaturefoundinSchoenebergerandothers(2002).

Mostofthesoilpropertiesaredescribedusinganumberofcomponentele-ments.Forexample,soilcolorisdescribedbythesixcomponentsofdryhue,dryvalue,drychroma,moisthue,moistvalueandmoistchroma(seetable1).Thissubdivisionofpropertiesresultedinalistof17propertiesand/orcomponentsthatcouldbeusedtodistinguishbetweenashyandnon-ashysoilhorizons.Eachcomponentofapropertyhasbeenassignedoneofseveralpossibleclassesthatdescribethecomponentforagivensoil.Forexample,drysoilhuecouldbe5YR,7.5YRor10YR.Tables2through6showtherelativefrequencydistributionforeachclassusedtodescribethecomponentsofeachsoilpropertybytephraornon-tephraparentmaterials.

Therelativefrequenciesobservedfortheclassesdescribingthecomponentsofeachsoilpropertywereusedtoevaluatewhichcomponentswouldbeusefulindiscriminatingandicfromnonandic(or“other”)materials.Ausefuldiscriminatorwasdefinedasonethatshowed:1)aclusteringof60percentormoreofobserva-tionsforthetephramaterialononecomponentclass,and2)lessthan35percentofobservationsforthe‘other‘materialsoccurringinthatsameclass.

ThepHofasuspensioncontaining1gsoilin50mL1MNaFisusedasatestfor thepresenceof short-rangeorderminerals.Theseminerals are commonlyearlyproductsoftheweatheringofpyroclasticmaterials.Theactionof1MNaFonthesemineralsreleaseshydroxideions(OH–)tothesoilsolutionandincreasesthepH.A1MNaFpHofmorethan9.4at2minutesaftertheNaFsolutionisaddedisastrongindicator(innon-calcareoussoils)thatshort-rangeorderminer-alsdominatethesoilexchangecomplex(Burt2004).


Field Identification of Andic Soil Properties for Soils of North-central Idaho Gardner

Table 1—Soil properties proposed as useful for field recognition of tephra derived soil materials with their component elements and descriptive classes.

Property Component elements Descriptive classesSoil color dry hue �YR, 7.�YR, 10YR dry value 2, 2.�, �, 4, �, �, 7 dry chroma 2, �, 4, � moist hue �YR, 7.�YR, 10YR moist value 2, 2.�, �, 4, �, �, 7 moist chroma 2, �, 4, �

Structure grade weak, moderate, strong sizea 1, 2, �, 4, � kindb abk, gr, pl, pr, sbk, massive

Consistence dry rupture resistance soft, slightly hard, moderately hard, hard, very hard moist rupture resistance very friable, friable, firm stickiness nonsticky, slightly sticky, moderately sticky, very sticky plasticity nonplastic, slightly plastic, moderately plastic, very plastic

Root abundancec very fine and fine roots few, common, many medium and coarse roots few, common, many

Textured none 1, 2, �, 4 ,� �, 7a Structure size classes are: 1 = very fine, very fine and fine or fine; 2 = very fine to medium or fine and medium; 3 = medium; 4 = fine to coarse or medium and coarse; 5 = coarse.b Structure kinds are: abk = angular blocky; gr = granular; pl = platy; pr = prismatic and sbk = subangular blocky.c Root abundance classes are: few = <2%, common = 2 to 20% and many = >20%.d Texture classes are: 1 = sil; 2 = l; 3 = fsl, vfsl; 4 = sicl; 5 = cl; 6 = sl; 7 = cosl, lcos for definitions of class terms see Schoenberger and others 2002.

Table 2—Observed frequencies for the components of soil color by moisture status and parent material.

Moist Dry Color tephra Other tephra Other component Classes count Freq count Freq count Freq count Freq

(no.) (no.) (no.) (no.) Hue 10yr 14� 0.�9 120 0.7� 240 0.74 1�� 0.90 7.�yr 229 0.�1 4� 0.2� �4 0.2� 14 0.09a

�yr 0 0 2 0.01 0 0 2 0.01

Value 2 0 0 � 0.02 0 0 0 0 2.� � 0.01 2 0.01 0 0 0 0 � 1�1 0.4� 4� 0.27 0 0 0 0 4 1�4 0.49 101 0.�0 2 0.01 11 0.07 � � 0.01 1� 0.10 127 0.�9 19 0.12 � 0 0 1 0.01 1�1 0.�� 104 0.�� 7 0 0 0 0 14 0.04 20 0.1�

Chroma 2 2 0.01 4 0.0� � 0.01 � 0.0� � �2 0.14 �� 0.41 21 0.07 �� 0.4� 4 2�� 0.�� 2 0.�� 2�1 0.�1 7� 0.�1 � �� 0.1� � 0.0� �� 0.12 � 0.0� a Component meets criteria for useful ashy soil identifier.



Table 3—Observed frequencies for the components of soil structure by soil parent material.

Structure Tephra Other component Classes count Freq count Freq

(no.) (no.)Structure grade weak 419 0.�� 14� 0.29a

moderate �� 0.1� �49 0.�� strong � 0.01 20 0.04

Structure size 1 2�1 0.�2 12� 0.24 2 204 0.40 290 0.�� 29 0.0� �0 0.12 4 1 0 29 0.0� � 9 0.02 11 0.02

Structure kind abk 0 0 2 0 gr 19� 0.�9 91 0.17 pl 0 0 11 0.02 pr 0 0 1� 0.0� sbk �11 0.�1 �9� 0.7� massive 1 0.00 1� 0.0�a Component meets criteria for useful ashy soil identifier.

Table 4—Observed frequencies for the components of soil consistence by soil parent material.

Consistence Tephra Other component Classes count Freq count Freq

(no.) (no.)Dry consistence soft(so) 474 0.9� 19 0.1�a

slightly hard (sh) 17 0.0� �2 0.24 moderately hard (mh) 1 0.00 �2 0.24 hard ( ha) 0 0.00 42 0.�2 very hard(vh) 1 0.00 � 0.0�

Moist consistence very friable(vfr ) �07 0.9� 2� 0.19a

friable(fr) 11 0.02 97 0.72 firm(fi) 0 0.00 12 0.09

Stickiness nonsticky(so ) 474 0.9� �4 0.2�a

slightly sticky(ss) �4 0.07 �� 0.�2 moderately sticky(ms) 0 0.00 1� 0.1� very sticky(vs) 0 0.00 1 0.01

Plasticity nonplastic(po) 4�� 0.91 1� 0.12a

slightly plastic(sp ) 4� 0.0� �1 0.�� moderately plastic(mp) 1 0.00 �4 0.40 very plastic(vp) 0 0.00 1� 0.11a Component meets criteria for useful ashy soil identifier.



Table 5—Observed frequencies for root abundance by root size class and soil parent material.

Root Tephra Other abundance Classes count Freq count Freq

(no.) (no.)Very fine and fine roots none 2 0 4 0.01 few 12 0.0� �� 0.07 common 9� 0.20 22� 0.47 many �� 0.77 21� 0.4�

Medium and coarse roots none 9� 0.20 171 0.�� few 1�� 0.�� 199 0.42 common 207 0.44 �� 0.1� many 1� 0.0� 1� 0.04

Table 6—Observed frequencies of soil textures (for the <2mm fraction) by parent material

Tephra OtherSoil texture name count Freq count Freq

(no.) (no.) sil (1) 4�� 0.99 �20 0.�7 l (2) � 0.01 112 0.2� fsl, vfsl (�) 0 0 10 0.02 sicl (4) 0 0 7 0.01 cl (�) 0 0 4 0.01 sl (�) 0 0 19 0.04 cosl, lcos (7) 0 0 � 0.01

Whileeachofthesevariablesisimportantinrecognizingashsoils,theclas-sificationcriteriaallowforinteractionbetweenthetwosothatnosinglevalueservestodiscriminateandicfromnonandichorizons.InanattempttodefinesuchathresholdvalueforNaF-pH,adatasetoflaboratorymeasurementsfromClearwa-terCounty,Idahowasobtainedforanalysis.Thedatasetcontained267horizonswithNaF-pHinformation.Thesewerethengroupedintoandic(73horizons)andnonandic(194horizons)soils.Table7reportsthemeanandstandarddeviationforthesetwosamplepopulations.Assuminganormaldistribution,itispossibletousethesemeansandstandarddeviationstocalculateaNaF-pHvaluethatcor-respondstothecriticalvaluefortheZstatisticatachosenlevelofprobability.Table7reportsthesecriticalvaluesasNaF-pHvaluesatP=.95andP=.99.

Table 7—Mean, standard deviation and NaF-pH values that are equivalent to the critical values of Z at two levels of probability.

Standard NaF-pH NaF-pH Mean deviation at P=.95 at P=.99

Nonandic �.�� 0.�0 9.�� 9.97

Andic 10.�� 0.�� 9.97 9.7�



Results and Discussion ___________________________________________Soilcolorisstronglyinfluencedbyparentmaterial(RichardsonandDaniels

1993).Table2indicatesthattheonlycomponentofsoilcolorusefulforrecognizingashinfluencedsoilsinnorth-centralIdahoisthemoisthue.Theash-influencedmaterialsarenoticeablyredderinhue(7.5YRvs.10YR)thanothermaterialsformostsamples.Thisisassumedtobearesultoftheprevalenceofferrihydriteinashymaterials(Dahlgrenandothers2004;UgoliniandDahlgren2002).Ferrihy-drite-containingsoilshavehuesof5-7.5YRwhilesoilswithhuesbetween7.5YRand2.5Ytendtocontainsignificantamountsofgoethite(Schwertmann1993).

Soilstructureisacomplexphenomenonthatdependsinpartonfactorssuchasparentmaterial,climateandthephysicalandbiochemicalprocessesofsoilformation (Brady andWeil 2001).Andic soils have a tendency tohaveweakfinestructurethatisgranularinAhorizonsandsubangularblockyinBhorizons(table3).Soilsderivedfromothermaterialshavesimilarstructuresizeandkindbutexhibitstrongerdevelopmentwithagradeofmoderatebeingdominant.Therefore,structuregradeisrecognizedasasuitableidentifierforash-influencedsoils.

Consistenceisadescriptionofasoil’sphysicalconditionatvariousmoisturecontentsasevidencedbytheresponseofthesoiltomechanicalstressormanipula-tion.Theconsistenceofasoilisdeterminedtoalargeextentbytheparticle-sizedistributionofthesoil,butisalsorelatedtootherpropertiessuchasorganicmattercontentandmineralogy(http://organiclifestyles.tamu.edu/soilbasics/soilphysical.html).Andicsoilshaveuniqueconsistencepropertiesdisplayinglowrupturere-sistance(inbothdryandmoiststates),littlestickinessandlowplasticity(table4).Eachofthesecomponentsofconsistenceisusefultoseparateashinfluencedfromothermaterials.Theyareareflectionoftheverylowclaycontentsanduniquemineralogyoftheashymaterial.

Fieldobservationshavenotedahighdegreeofrootproliferationinashysurfacehorizonsinnorth-centralIdaho.Whilethedatashowaslighttrendtowardgreaterrootabundanceintheashymaterials,thedifferencecomparedtotheotherparentmaterialswasnotsufficienttoallowuseofthischaracteristicasadiscriminator(table5).Therecordingofrootabundanceasbroadclassesratherthanactualcountsperareamayhavereducedtheusefulnessofthiscomparison.

Aseriesofsimplemodelsforrecognizingash-influencedsoilmaterialswerecreatedusingthecomponentsidentifiedasusefuldiscriminatorsofashymaterial.Theyweretestedthroughaprocessoftrialanderror.Duringthistestingitwasdiscoveredthatsoiltexturecouldbeusedtohelpimprovemodelperformance.Thisistrueeventhoughthatpropertydidnotmeetthecriteriasetforrecogni-tionasausefuldiscriminator.Soiltextureprovedtobeaspecialcasewherethehighdegreeofclusteringon thesilt loamclass (99.6percentofobservations)fortheash-influencedmaterialhelpedthemodeltorecognizethesematerials.Thisimprovedperformanceresultsfrombetterseparationoftheash-influencedmaterialsfromlowplasticitymaterialsofotherorigins.Duringthisphase,itwasalso determined that moist rupture resistance would not be used in the finalmodel.Eventhoughthiscomponentmetthecriteriaforausefuldiscriminator,itisstronglyrelatedtodryruptureresistance.Theadditionofmoistruptureresis-tancedidnotimprovethemodel.Dryruptureresistancewaspreferredbecauseithadmore-easilyrecognizedclassesandgreaterconsistencyinapplicationbydifferentobservers.



Afinalmodelwascreatedforevaluatingwhetherasoilsampleclassifiesasandicmaterial.Themodelscoresasoilbasedonthesixidentifiedpropertiesand/orcomponentsasfollows:

moisthue–7.5YR=1,other=0;structuregrade–weak=1,other=0;dryruptureresistance–soft=2,other=0;stickiness–nonsticky=2,other=0;plasticity–nonplastic=2,other=0;texture–siltloam=2,other=0.Ascore>=8isandicmaterialwhile<8isnonandic.

Thismodelwasusedtoevaluatetheoriginaldatasetandreturnedanerrorrateof7.6percent.Therewereapproximatelyequalpercentagesoffalsepositivesandfalsenegatives.Of the468horizonsdesignatedashyby theexpertobservers,themodel failed torecognize37.These37falsenegativesweredueprimarilytotheirlackoftheexpectedmoisthueandplasticitycharacteristics.Ofthe477horizonsdesignated-non-ashybyexpertobservers,35weremisidentifiedbythemodelasandicmaterials.These35horizonsaresiltloamsthatarelowinclayandthathaveruptureresistance,stickinessandplasticitycharacteristicssimilartoandicmaterials.Themodelcorrectlydiscriminatedbetweenandicandnonandicmaterialsin92.4percentofcases.

NaF-pHhasbeenidentifiedasasimpleandconvenientindexforthepresenceofandicmaterials(FieldesandPerrott1966).WorkbyKimseyandothers(2005)foundastrong(R2=.82)correlationbetweenNaF-pHandacidoxalateextractableAlandFe.AnotherstudybyBrownfieldandothers(2005)reportedagoodcor-relation(R2=.66)betweentephrapercent(basedongraincounts)andNaF-pH.AcriticalpHvalueof9.4hasbeensuggestedasthethresholdforrecognitionoftephradominatedmaterials(SoilSurveyStaff1995).Thecalculationsshownintable7indicatethat,fortheClearwaterCountydata,thisthresholdvalueistoolow.Thetableshowsthat95percentof thedistributionofNaF-pHvalues forandichorizonsisgreaterthanorequalto9.97.Interestingly,thesameNaF-pHvalueof9.97istheupperboundbelowwhich99percentofthedistributionofnonandicvaluesisfound.RoundingtoonedecimalplacegivesaNaF-pHof10.0asasuggestedthresholdforrecognizingandicmaterials.WhenappliedtotheClearwaterCountydata,thisthresholdcausesanerrorrateofabout10percent(7outof73horizonsmisidentified)forandichorizonsandabout3percent(6outof194horizonsmisidentified)fornonandichorizons.UsingathresholdpHvalueof10.0allowedforcorrectclassificationofhorizonsinabout95percentofcases.

Summary ______________________________________________________Twomethodsforfieldidentificationofvolcanicashinfluencedsoilhorizons

were explored. A simple empirical model was developed for ash recognitionusingtheeasilyobservablequalitativepropertiesofmoisthue,structuregrade,dryruptureresistance,stickiness,plasticityandtexture.Thismodelsuccessfullydiscriminatedbetweentephraandothermaterialsinabout92percentofcases.Amodellikethiscanbeusedtohelpthosenotexpertinsoilclassificationtorecognizeandicsoilmaterials,toevaluatewrittendescriptionswhensoilsamples

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arenotavailableandtohelpmoreexperiencedsoilclassifiersinconditionswherethetephraishighlymixedwithothermaterials.OneprincipalweaknessofthismodelisthatitisdevelopedforMountMazamaashinnorth-centralIdaho.Soilsformedinvolcanicejectainotherareasmayhaveadifferentsetofidentifyingcharacteristics.

ThesecondmethodforidentificationofandicmaterialswastheuseofNaF-pH.Whiletheanalysisusedheredependedonlaboratorymeasurements,theNaF-pHcanbereadilymeasuredinthefield.DatafromClearwaterCounty,Idahoshowedthatusingathresholdvalueof10.0pHunitscorrectlyclassifiedsoilhorizonsinabout95percentofcases.TheuseofNaF-pHtodetectallophanicmaterialhasbroadapplicationtomanydifferentvolcanicmaterials.However,identificationofthemostusefulthresholdvaluemaybesubjecttoregionalvariation.

Literature Cited __________________________________________________Brady,N.C.;Weil,R.R.2001.TheNatureandPropertiesofSoils.13thedition.Englewood,NJ:

PrenticeHall.960p.Brownfield,S.H.;Nettleton,W.D.;Weisel,C.J.;Peterson,N.;McGrath,C.2005.Tephrainfluence

onSpokane-floodterraces,BonnerCounty,Idaho.SoilSci.Am.J.69:1422-1431.Burt,R.,ed.2004.SoilSurveyLaboratoryMethodsManual.SoilSurvey InvestigationsReport

No. 42. Version 4.0. Natural Resources Conservation Service, National Soil Survey Center,Lincoln,NE.

Dahlgren,R.A.;Saigusa,M.;Ugolini,F.C.2004.Thenature,propertiesandmanagementofvolcanicsoils.In:Sparks,D.,ed.AdvancesinAgronomyVol.82.AcademicPress:113-182.

FAO/ISRIC/ISSS.1998.WorldReferenceBaseforSoilResources.Rome:FoodandAgriculturalOrganizationoftheUnitedNations,InternationalSoilReferenceandInformationCentre,andInternationalSocietyofSoilScience.WorldSoilResourcesReportNo.84.Available:http://www.fao.org/docrep/W8594E/W8594E00.htm.

Fieldes,M.;Perrott,K.W.1966.Thenatureofallophaneinsoils.III.Rapidfieldandlaboratorytestforallophane.NewZealandJ.Sci.9:623-629.

Kimsey,MarkJr.;McDaniel,Paul;Trawn,Dan;Moore,Jim.2005.Fateofappliedsulfateinvolcanicash-influencedforestsoils.SoilSci.Soc.Am.J.69:1507-1515.

McDaniel,P.A.;Wilson,M.A.;Burt,R.;Lammers,D.;Thorson,T.D.;McGrath,C.L.;Peterson,N.2005.AndicsoilsoftheInlandPacificNorthwest,USA:Propertiesandecological

significance.SoilScience.170:300-311.Richardson,J.L.;Daniels,R.B.1993.Stratigraphicandhydraulicinfluencesonsoilcolordevelop-

ment.In:Bigham,J.M.;Ciolkosz,E.J.,eds.SoilColor.SSASpecialPub.No.31:109-125.Schoenberger,P.J.;Wysocki,D.A.;Benham,E.C.;Broderson,W.D.,eds.2002.Fieldbookfor

samplinganddescribingsoils.Version2.0.NaturalResourcesConservationService,NationalSoilSurveyCenter,Lincoln,NE.

Schwertmann,U.1993.Relationsbetweenironoxides,soilcolor,andsoilformation.In:Bigham,J.M.;Ciolkosz,E.J.,eds.SoilColor.SSASpecialPub.No.31:51-69.

Shoji,S.;Nanzyo,M.;Dahlgren,R.A.1993.Volcanicashsoils:Genesis,properties,andutiliza-tion.In:Hartemink,A.E.;McBratney,A.,eds.Developmentsinsoilscience,21.Amsterdam,TheNetherlands:Elsevier.

SoilSurveyStaff.1995.SoilsurveyLaboratoryManual.WoilsurveyInvestigationsReportNo.45.NationalSoilSurveyCenter.SoilSurveyLaboratory,Lincoln,NE.81p.

SoilSurveyStaff.1999.Soiltaxonomy.Abasicsystemofsoilclassificationformakingandinter-pretingsoilsurveys.2nded.U.S.DepartmentofAgriculture,NaturalResourcesConservation.

Ugolini,F.C.;Dahlgren,R.A.2002.Soildevelopmentinvolcanicash.Available:http://www.airies.or.jp/publication/ger/pdf/06-2-09.pdf.

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P. A. McDaniel is a Professor of Soil Science, Soil & Land Resources Division, University of Idaho, Moscow, ID. M. A. Wilson is a Research Soil Scientist, U.S. Department of Agriculture, Natural Resources Conservation Service Soil Survey Center, Lincoln, NE.

Abstract HoloceneashfromthecataclysmiceruptionofMountMazama(nowCraterLake)insoutheasternOregonisamajorcomponentofmanyforestsoilsthatlietotheeastofCascadeMountainsinthePacificNorthwestregion.Therelativelyhighproductivityoftheregion’secosystemsiscloselylinkedtothisvolcanicashcomponent.Thispaperreportsontheecologicallyimportantpropertiesoftheseash-influencedsoilsbyexaminingsoilcharacterizationdatafromover500soilhorizonsoftheregioncontainedintheNationalSoilSurveydatabase.Volcanicash-captexturesaregenerallysiltyinareasdistaltotheeruption.Volumetricwater-holdingcapacityofash-caphorizonsisasmuchastwicethatofunderlyinghorizonsandunderscorestheimportanceofashcapsinseasonallydry,forestedecosystemsoftheInlandNorthwestregion.Cationexchangecapacity(CEC)determinedatfieldpH(ECEC)averages8.0cmolckg–1andislessthanone-thirdtheCECdeterminedatpH8.2,indicatingconsiderablevariablecharge.Thesedatasuggestthatash-influencedsoilshavelimitedabilitytostoreandexchangenutrientcationssuchasCa,Mg,andK.Inaddition,strongsorptionofSO4andPO4significantlylimitsthebioavailabilityofthesenutrients.Erosionandcompactionofashcapsaremajormanagementconcerns,butrelationshipsbetweentheseprocessesandash-capperformanceremainunclear.

Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests

P. A. McDaniel and M. A. Wilson

Introduction

Soilsformedentirelyorpartiallyinvolcanicejectasuchasash(glassyparticles<2mminsize),cinders (glassyparticles>2mminsize),andpumice (highlyvesicular fragments)arefundamentallydifferentfromothersoilsintermsoftheirphysical,chemical,andmineralogi-calproperties.Becauseofthis,Andisolswereestablishedasthe11thsoilorderinU.S.SoilTaxonomyin1989.TheWorldReferenceBaseofSoilResources(WRB)alsorecognizesthesesoilsasAndosols,oneofthe30soilreferencegroups(FAO/ISRIC/ISSS1998).Soilsformedinvolcanicash,suchastheash-capsoilsfoundinthePacificNorthwestregion,arecharacter-izedbywhatarereferredtoasandic propertiesinSoilTaxonomy(SoilSurveyStaff2003).Andicpropertiesrefertoacombinationofcharacteristics,includingthepresenceofglass,short-range-orderorpoorlycrystallineweatheringproductswithhighsurfacereactivity,andlowbulkdensity.


McDaniel and Wilson Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests

VolcanicashfromtheeruptionofMt.Mazama(nowCraterLake,OR)~7,700yearsBP(Zdanowiczandothers1999)hasinfluencedmanymid-tohigh-elevationfor-estsoilsinthePacificNorthwestregion.Theuniquepropertiesoftheseash-capsareintricatelylinkedtoforestproductivityacrosstheregion(GeistandCochran1991;Meurisseandothers1991).Assuch,thesesoilsrepresentavaluableregionalresourcefrombothaneconomicandecologicperspective.Moreover,ash-capsoilsresponddifferentlytouseandmanagementthandosoilsformedinotherparentmaterials,anditisthereforeimportanttorecognizeandunderstandthebasicdifferencesinproperties.Inthispaper,wedescribesomeoftheimportantcharacteristicsofvolcanicash-influencedsoils.

WeusedtheNaturalResourcesConservationService(NRCS)—SoilSurveyLaboratorycharacterizationdatabaseforWashington,Oregon,Idaho,andMontanatoprovideanoverviewofphysicalandchemicalcharacteristicsofvolcanicash-capsoilsoftheregion.Thesoilsinthisdatabasearerepresentativeofthedomi-nantmappingunitcomponentsinsoilsurveyareas,andhavepropertiesthatareconsideredtypicalofsoilsacrosstheregion.Forinclusioninthedatabase,weidentifiedallhorizonsmeetingeitherthecriteriaforandicsoilpropertiesorandicsubgroupsinSoilTaxonomy(SoilSurveyStaff2003).Allcharacterizationdatawereobtainedusingstandardmethods(Burt2004)andhavebeensummarizedinMcDanielandothers(2005).

Soil Morphology ________________________________________________ThethicknessofashcapsacrosstheInlandNorthwestregionisvariable,but

followsageneraltrendofthinningwithincreasingdistancefromCraterLake(fig.1a).DatapresentedbyMcDanielandothers(2005)showedarangeinthicknessof2to152cmacrosstheregion,withanaveragethicknessof38cm.Itshouldbenotedthatthesereportedthicknessesincludeashcapsthinnedbyerosionaswellasthoseinwhichothersoilparentmaterialshavebeenmixedwiththevolcanicashafterinitialdeposition.Inthelattercase,thereportedthicknessesrepresentthoseofash-influencedmantlesratherthanpureashmantles.Itisimportanttorealizethattheashcapsfoundacrosstheregionhavebeenmixedtovaryingdegreesbypost-depositionalprocessesandrepresentarangeincomposition.Forpurposesofthispaperandotherscontainedintheseproceedings,thetermash capwillbeusedtoincludeallashmantles,regardlessofdegreeofmixing.

Mostoftheofficialsoilseriesdescriptions(SoilSurveyDivision2005)forash-capsoilsoftheregionincludeforestlitterlayersthatareunderlainbyAhorizonshavingthicknessestypicallyrangingfrom2.5-7.5cm(1-3inches).ThedevelopmentofAhorizonsformedinvolcanicashintheInlandNorthwest isusuallyweakdespitethefactthatash-capsoilsgenerallycontainrelativelylargeamountsoforganicmattercomparedtoothermineralsoils(Dahlgrenandothers2004).Thisweakdevelopmentisprobablyduetothefactthatmostash-influencedsoilsareforestsoils,wherethemajorityofcarboniscontainedinlitterlayersandrelativelysmallquantitiesareaddedtoAhorizonsintheformofroots.Thisfactorresultsinrelativelythin,light-coloredAhorizons.Verydark-coloredAhorizonscanforminvolcanic-influencedsoils thatsupportgrassesorunderstoryvegetationwithextensiverootsystems.Deep,darkAhorizonshavebeendescribedunderbrackenfern(Pteridium aquilinum)communitiesinnorthernIdaho(Johnson-Maynardandothers1997).Thesecommunitiesmayhaveasmuchas3,500g/m2ofbelowgroundbiomassintheformofrhizomesandfineroots(Jimenez2005).

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Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests McDaniel and Wilson

Figure 1—Change in (a) ash-cap thickness and (b) particle-size distribution of Mazama tephra as a function of distance from Crater Lake, OR. Particle-size data represent averages for the ash caps of Lapine, Angelpeak, Threebear, and Jimlake soils and are adapted from McDaniel and others (200�).

UnderlyingtheAhorizonsarereddish-toyellowish-brownBwhorizonsthatdonotexhibitsignificantincreasesinclaycontent.Huesofthesesubsoilhorizonsaretypically7.5YRto10YRwithchromasof4or6.ThesecharacteristiccolorsreflecttheweatheringofashtoformpoorlycrystallineFeoxidessuchasferrihy-drite(McDanielandothers2005).

Insomehigher-elevationareas,ash-capsoilsmayhaveundergonesufficientpodzolizationtodevelopE-Bh,Bhshorizonsequences.Thesesoilsaretypicallyinhigh-precipitationenvironmentsandhaveextremelyacidEhorizons.IntheSelkirkMountainsofnorthernIdaho,pHvaluesaslowas3.7havingbeenre-ported(McDanielandothers1997),thelowestpHvaluesfoundanywhereintheregionfornativesoils.



Physical Properties ______________________________________________

Particle-Size Distribution

MuchofthetephradistributedthroughoutthePacificNorthwestwascarriedinsuspensionbyprevailingwesterlywinds,aprocessthathasresultedinfairlydistinctrangesofparticlesizesassociatedwithashcaps.Examinationofashcaptexturesacrosstheregionshowsadecreaseinoverallparticlesizewithincreas-ingdistancefromthesource(fig.1b).ThepumiceregionsofcentralOregonareincloserproximitytoCraterLake,andsand-sizedpumicedominatesinsoilslikeLapine.However,ashcapsfromtheBlueMountains(e.g.Angelpeaksoil),northernIdaho(Threebearsoil),andwesternMontana(Jimlakesoil)arepredominantlysilt-sized,reflectingthegreaterdistanceoftransport.Fine-earthfractionsoftheseashcapstypicallyhavesiltloamorloamtextures,whichcansubstantiallyenhancethewater-holdingcapacityofsoilprofiles.

Bulk Density

BulkdensityofAndisolstendstoberelativelylow,andthisisoneofthedefiningcharacteristicsofthesesoilsinSoilTaxonomyandtheWRB.Ofthe271horizonsexaminedacrosstheregion,theaveragebulkdensityis0.90gcm–3(fig.2).How-ever,only~60perecentofthehorizonshavebulkdensitiesof<0.90gcm–3,sug-gestingthatmixingand/orcompaction,bothofwhichwouldtendtoincreasebulkdensity,haveoccurredsincedeposition.Becausebulkdensityisinverselyrelatedtoporosity,anashcapwithabulkdensityof0.90gcm–3mayhave~40percentmoreporositythanatypicalmineralsoilwithabulkdensityof1.3gcm–3.

Figure 2—Bulk density data for andic soil horizons of the Pacific Northwest region. Taken from McDaniel and others (200�).



Water-Holding Capacity

Andisols typically are able to retain large amounts ofwater (Dahlgren andothers2004).IntheInlandNorthwestregionwhereextendeddryperiodsoftenoccur during the growing season, this water-holding capacity is arguably themostimportantpropertyfromanecologicalstandpoint.Additionalwater-holdingcapacityassociatedwithash-capsoilsmaybecriticaltotheestablishmentandmaintenanceofsomeplantcommunities.Thebasisfortheadditionalwater-holdingcapacityimpartedtosoilsbyvolcanicashstemsfromthreefactors.First,asdis-cussedpreviously,ashcapshaverelativelyhighporosity.Secondly,muchofthedistalashissilt-sized,whichisdesirablefromthestandpointofwaterretentioncharacteristics.Thisisespeciallytrueinmanymountainousareaswherevolcanicashoverliescoarser-textured,oftenrockysoilswithrelativelylittleplant-available-water-holdingcapacity.Finally,weatheringofvolcanicashgivesrisetoacolloidalfractionthathashighsurfaceareaandisabletoretainconsiderablequantitiesofwater(Wada1989;Kimbleandothers2000;Dahlgrenandothers2004).

Theeffectofavolcanicashcaponthewater-holdingcapacityofanorthIdahosoilisillustratedinfigure3.Theashcapconsistsofthetoptwohorizons,whichhavemorethantwicethewater-holdingcapacity(onavolumebasis)oftheun-derlyingcoarser-texturedhorizonthathasformedinoutwash.Inthisexample,theashmantlecontributes8.6cm(~3.4inches)ofplant-availablewatertothesoilprofile.Ash-capsoftheregionhaveanaveragewaterretentionof~11percent(byweight)at1,500kPaofsoilmoisturetension(wiltingpoint)(McDanielandothers2005),orroughlytwicethatofsandysoils(BradyandWeil2004).

Figure 3—Water retention difference in the top �0 cm of the Bonner series (��ID017002) from north Idaho. Bars represent the difference in water content between –1,�00 and –�� kPa, expressed on a volume basis and corrected for rock fragment content. Shaded bars are for andic materials.

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Whencomparingorinterpretingwaterretentiondata,itisimportanttodistin-guishbetweendatareportedonagravimetric(weight)andthosereportedonavolumebasis.Becausesoilhorizonsformedinvolcanicashtypicallyhavebulkdensities<1.0g/cm3,watercontentswillbegreaterwhenexpressedonaweightbasisratherthanavolumebasis.Theoppositeistrueforothermineralsoilswithbulkdensities>1.0g/cm3.

A mantle or cap of volcanic ash also contributes to a more-favorable soilmoistureregimethroughamulchingeffect.Someoftheincreasesincropyieldsobservedafterthe1980MountSt.Helenseruptionwereattributedtothedeposi-tionoffreshashanditsroleinreducingevaporativewaterlosses(Dahlgrenandothers2004).

Other Physical Properties

SomeAndisolsexhibitthixotropy,whichisdescribedasareversiblegel-sol-geltransformation (Nanzyo and others 1993b). Upon application of pressure orvibration,awetsoilmasswillexperienceasuddenreversible lossofstrengthandbegintoflow.Itcaneasilybeobservedinawell-moistenedash-capsample.Byapplyingpressure to thematerialbetweenthethumbandforefinger,watercanbeforcedoutofthesoilmass;releaseofpressurewillcausethenwatertobere-absorbed.Onalargerscale,thixotropycanresult insoilcollapseunderroadwaysandbuildingfoundations(BradyandWeil2004).Thixotropyismostpronouncedinhighlyweatheredsoilsformedinvolcanicash(Buolandothers2003),andthereforeisnotoftenwellexpressedintherelativelyless-weatheredash-capsoilsoftheInlandNorthwestregion.Soilsformedinvolcanicashalsohavealowbearingcapacitybecauseoftheirlowbulkdensity(Kimbleandothers2000),andthismakesthemsusceptibletocompactionandcancreateproblemsfortraffickingandbuildingfoundations.

Mineralogical Properties _________________________________________

Volcanic Glass

TheprincipalcomponentofMazamavolcanicashisglass,whichwasformedbytheveryrapidcoolingofrhyodaciticmagmaasitwasejectedfromthevolcanoduringtheclimaticeruption(fig.4)(Bacon1983).Theamountofglassinvolcanicashmantlesacrosstheregionisvariable,andmostlikelyreflectspost-depositionalredistribution.IntheBlueMountainsofnortheasternOregonandsoutheasternWashington,relativelyundisturbedashmantlescontain60-90percentvolcanicglassandarefoundinmoisterlandscapepositionswithlowerfirefrequency(Wil-sonandothers2002).Inotherareaswithmoreactivesurficialprocessessuchaserosionafterfire,glasscontentsrangesfrom25-60percent,andthesearereferredtoasmixedmantles(Wilsonandothers2002).Theglasscontentof528ash-capsoilhorizonsoftheregionthatmeetandicsoilrequirementsinSoilTaxonomyaverages~42percentandexhibitsabimodaldistribution(McDanielandothers2005).Thissuggeststhatmixedmantlesarecommonacrosstheregion,andthatlocally,underlyingsoilshaveatleastsomeinfluenceonashcapproperties.



Analysis of Mazama ash deposits shows an elemental composition of 70-72percentSiO2(Bacon1983).Inaddition,McDanielandothers(1997)reportedthatthecombinedAl2O3andSiO2contentofMazamaglasswas~87.5percent,withtheCaO,MgO,andK2Ocontentscomprisingonly4.9percentbyweight.Forcomparativepurposes,Bohnandothers(2001)reportanaverageCaO,MgO,andK2Ocontentforavarietyofigneousrocksof12percent.Itisclearfromthesedata thatvolcanicglass isnota rich sourceofplantnutrientsandshouldnotbethoughtofasahavingremarkablefertility.MinoramountsofplantnutrientssuchasSO4

2–,Ca2+,andPO42–presentintheoriginalMazamaashfallmayhave

providedshort-termfertilityinputs,aswasthecasewiththe1980eruptionofMountSt.Helens(Fosbergandothers1982;Mahlerandothers1984).However,long-termfertilityoftheglassisrelativelylow.

Clay Mineralogy

Becauseofthelackofacrystallinestructure,glassweathersrelativelyrapidlytoformpoorlycrystallineornon-crystallinemineralsintheclayfraction.InslightlytomoderatelyweatheredAndisolssuchasthosefoundinthePacificNorthwestregion,therearethreemineralassemblagesthattendtodominate:(1)Al-humuscomplexes,oftenwithAl-hydroxy-interlayered2:1minerals; (2)allophaneandimogolite,and;(3)poorlycrystallineFeoxides(ferrihydrite)(Dahlgrenandothers2004).Asashweathers,AlandFereleasedintosoilsolutioninsurfacehorizonscanformstableorganiccomplexes,especiallyatsoilpH<5(ParfittandKimble1989);thesepHvaluesarecommonunderconiferousforestvegetationathigherelevationintheInlandPacificNorthwest.Al-humuscomplexesrepresentactive

Figure 4—Volcanic glass shard from north Idaho soil. Glass is from the Mazama eruption and measures ~0.1 mm across. Photo from University of Idaho.



formsofAlandmaycontributetoAltoxicity(Dahlgrenandothers2004).Intherelativeabsenceofhumusandlessacidconditions,suchasinBandChorizons,AlandSiprecipitatetoformallophaneandimogolite.Thesetwoaluminosilicatemineralsmayhavesimilarchemicalcomposition,butallophanetypicallyconsistsofsphericalunitswhileimogoliteappearsasthreadsortubes(Kimbleandothers2000).Allophaneand imogolitebothhave relativelyhigh surfacearea.UsingdatapresentedbyHarshandothers(2002),WhiteandDixon(2002),andMalla(2002),thesurfaceareaofimogoliteisasmuchas100timesgreaterthanthatofkaoliniteand40percentgreaterthanthatofvermiculite.Thisimportantpropertyisdirectlyrelatedtoboththehighwater-holdingcapacityandchemicalreactivityoftheseminerals.

Chemical Properties _____________________________________________

Soil Reaction

Themajorityofandicsoilhorizonsoftheregionaremoderatelytoslightlyacid.Approximately70percentof thehorizonsexaminedhavepHvaluesbetween5.6and6.5,withanaveragepHof6.02(fig.5).ThispHrangeisgenerallysuitableforplantgrowth,asmanynutrientsarepresentinplant-availableformswithinthisrangeandthepotentialforaluminumtoxicityislow(BradyandWeil2004).

Cation/Anion Exchange

Oneoftheimportantfeaturesofsoilsformedinvolcanicashisthevariablechargeassociatedwith thecolloidal fraction.Variablecharge,also sometimesreferredtoaspH-dependentcharge,meansthatthenetsurfacechargedepends

Figure 5—Soil pH data for ash-cap soil horizons from the Inland Pacific Northwest region.



onthepHofthesoilsolution(SoilScienceSocietyofAmerica2001).Itisthisnetsurfacechargethatdeterminesthecationexchangecapacity(CEC)ofasoilanditsabilitytoretainandexchangenutrientcationssuchasCa2+,Mg2+,andK+.TheCECofandicsoilsdecreaseswithdecreasingpH,andmayinfact,bequitelowattheacidicpHvaluesthatcharacterizemanyforestsoils.Moreover,someandicsoilsmayhavesubstantialanionexchangecapacity(AEC)atacidicfieldpHvalues(Kimbleandothers2000),influencingtheretentionofionssuchaschlorideandnitrate.AlthoughPO4

2–andSO42–ionsaresorbedthroughanion

exchange, fixation of these ions (described below) is much greater than thisexchangereaction.

TheeffectofvariablesurfacechargeisillustratedbyCECandbasecationdatafromash-capsoilsacrosstheregion.Table1showsCECvaluesdeterminedfor515horizonsusingthreeprocedures.Thelowestvaluesareforeffectivecationexchangecapacity(ECEC),wheretheCECisdeterminedatthepHofthesoil.ThehighestvaluesareforCECdeterminedatpH8.2(CECpH8.2),whichisconsiderablyhigherthanthesoilpHoftheregion.AlthoughthislattermethodoverestimatestheCECthatexistsinthefield,thedifferenceinECECandCECpH8.2valuesillus-tratesthepotentialvariablechargethatexistsinthesesoils.Onaverage,CECpH8.2valuesareapproximatelyfourtimesgreaterthanECECvalues.

Table 1—Exchange properties of andic soil horizons of the Inland Northwest Region. Adapted from McDaniel and others (200�).

Ca2+ Mg2+ K+ Base saturation1 ECEC2 CEC pH 7 CEC pH 8.2

- - - - (cmolc /kg) - - - - (%) - - - - - - - - (cmolc /kg) - - - - - - - - Average 7.2 1.� 0.� 4�.0 �.� 19.1 2�.4 n �1� �1� �14 �14 11� �1� �1� Std. deviation �.7 2.0 0.7 2�.� �.4 11.� 1�.� Minimum 0 0 0 1 0.� �.4 7.0 Maximum ��.2 24.0 9.1 100 4�.7 101.0 12�.2

Anotherimportantcharacteristicofash-capsoilsistheirabilitytostronglyadsorbandimmobilizeplant-availableformsofPandS.Thisprocess,knownasfixation,resultsinlowconcentrationsofPO4

2–andSO42–insoilsolutionand

availableforplantuse(fig.6).TheabilitytofixPO42–resultsfromthestrongat-

tractionbetweenPO42–andtheedgesofallophane,imogolite,andferrihydrite,

andthereareprobablyseveralsorptionmechanismsinvolved(Wada1989).HighPO4

2–sorptionisoneofthecharacteristicsusedtodefineandicsoilpropertiesinSoilTaxonomyandandichorizonsinWRB.



Figure 6—Sorption isotherms for (a) phosphorus additions (adapted from Jones and others 1979), and (b) sulfate additions (adapted from Kimsey and others 200�). Data points represent the proportions of sorbed (plant unavailable) and soluble (plant available) forms with additions of increasing quantities of phosphorus and sulfate.

Allophanic and Non-allophanic Andisols __________________________Becauseoftherangeincharacteristicsofvolcanicash-capsoils,arelatively

simpleclassificationschemehasbeendevisedthatrecognizesthesedifferencesfromamanagementperspective.Thissystemclassifiessoilsaseitherallophanicornon-allophanic(Nanzyoandothers1993a;Dahlgrenandothers2004).Allo-phanicAndisolsarethosethataredominatedbyinorganicweatheringproductssuchasallophaneandimogolite.Incontrast,organicallyboundcomplexesaremuchmoreimportantinnon-allophanicAndisols.Propertiesofthesetwoclassesofash-derivedsoilsaresummarizedintable2.Ingeneral,non-allophanicsoilspresentmoremanagementchallenges.Thesesoilshaveseveralpropertiesthatmayinhibitplantgrowth—greateracidityandgreaterpotentialforAl3+toxicity



aretwoofthemostimportant.MostofthesoilsintheInlandNorthwestregionareclassifiedasallophanic(McDanielandothers2005).However,researchhasshown that shifts fromallophanic tonon-allophanicpropertiesandviceversacanoccurrelativelyquicklywithchangesinvegetation.AnexampleofthisfromnorthernIdahoisdescribedinthefollowingsection.

Response to Management _______________________________________

Erosion

Thescientific literaturecontainssometimes-contradictory informationaboutsusceptibilityofash-capsoilstoerosion.Soilsformedinvolcanicasharetypi-callydescribedashavingstrongresistance toerosion, largelyasa functionofstableaggregationandhighinfiltrationrates(Nanzyoandothers1993b;Dahlgrenandothers2004).However,becauseoftheirlowbulkdensitytheymaybeverysusceptibletowindandwatererosionwhenvegetativecoverisremoved(Kimbleand others 2000; Arnalds and others 2001). In the Inland Northwest region,maintenanceofforestcover,includingbothcanopyandlitterlayers,hasbeenanimportantfactorintheretentionofMazamaashcapsoverthemillenniasincedeposition(McDanielandothers2005).Thesefactorssuggestthaterodibilityofvolcanicashcapsisrelatedtodegreeofdisturbance;disturbancethatdestroysorremovescanopyandlitterlayerswilllikelyleadtosevereerosion.

Compaction

Perhapsoneof thebest-documentedresponsesofash-capsoils toland-useactivitiesiscompaction.Asdescribedearlier,andicsoilsaredefinedinpartbyabulkdensityof<0.90g/cm3.Numerousstudieshaveshownsignificantincreasesinash-capbulkdensityasaresultoftimberharvesttrafficking.IntheBlueMoun-tainsofeasternOregonandWashington,averagebulkdensity increasedfrom0.669gcm–3inunharvestedareasto0.725gcm–3inharvestedareas,represent-inganaverageincreaseof~9percent(Geistandothers1989).However,larger

Table 2—Comparison of properties of allophanic and non-allophanic Andisols (adapted from Dahlgren and others 2004; Nanzyo and others 199�a).

Property Allophanic Non-allophanicpH slightly to moderately acid strongly acid

Dominant mineralogy allophane/imogolite Al-interlayered 2:1 layer silicates and Al-organic complexes

Organic matter content moderate moderate to high

Al toxicity rare common

Compaction potential slight moderate



bulkdensity increaseswereassociatedwithskid trailsand landings.Similarly,Cullenandothers(1991)reportedsignificantincreasesinash-capbulkdensityinmoderatelyandseverelytraffickedareasascomparedtonon-harvestedcontrols.In addition, they were able to quantify changes in soil hydrologic propertiesaccompanyingbulkdensityincreases.Watercontentatrelativelylowsoilmois-turetensionsdecreasedsignificantlyintraffickedareascomparedtothecontrols(Cullenandothers1991)(fig.7a).One-hourinfiltrationdecreasedaswell,withvaluesdecreasingfrom38.5cminthecontrolto7.3cmintheseverelytraffickedareas(Cullenandothers1991).

Figure 7—Changes in (a) water content of ash-cap soils due to timber harvest trafficking, and (b) 1-hour infiltration in ash-cap soils due to timber harvest traf-ficking. *, ** indicate values that differ from the untrafficked controls at the 0.01 and 0.0� significance levels, respectively. Data are adapted from Cullen and others (1991).



Chemical/Mineralogical Changes

WorkbyJohnson-Maynardandothers(1997)innorthernIdahosuggeststhatdevelopmentofnon-allophanicpropertiesaccompaniesestablishmentofbrackenferncommunitiesafterclearcuttinginaslittleas30yearsandmaycontributetotheobservedlackoftimberregeneration.ThissubjectisdiscussedinmoredetailbyFergusonandothers (thisproceedings).Recent literature suggests that thismineralogicalconversionisnotirreversible.Takahashiandothers(2006)reportedthatadditionsoflimetonon-allophanicsoilswillraisepHandreducetheactiveformsofAl3+,therebyrepresentingapotentialreclamationstrategy.

Knowledge Gaps ________________________________________________Twomajorquestions related to thepropertiesandmanagementof ash-cap

soilsintheInlandPacificNorthwestregionremain.Thefirstquestionis:How much ash is there and where is it?Thisseemslikeabasicquestion,yetitisoneforwhichagoodanswerdoesnotcurrentlyexist.TheNationalCooperativeSoilSurveyprogramhasproduced in~1:24,000-scale soil surveys forpartsof theregion,andtheseprovidesufficientdetailtoassesstheextentandspatialdistri-butionofash-capsoils.However,muchoftheforestedlandareawhereash-capsoilsare foundhasnotbeensubject to this typeofsoilmapping.Asa result,detailedinformationabout thequantitiesandspatialdistributionofashacrosstheregionisoftenlacking,poorlydocumented,and/ornotreadilyaccessible.Developmentofmodelsthatpredictashcapdepthanddistributionwill likelybegreatlyenhancedbynewtechnologies in remotesensing.However, in theabsenceofmoredetailedmappingorpredictivemodels,atestsuchastheNaFpHmeasurementcanprovideaquickandeasy indicatorofash-capsoils.AnNaFpHvalue>9.4generallyindicatesthepresenceofweatheredvolcanicash(FieldesandPerrott1966;Wilsonandothers2002)andservesasaguidelineforidentifyingash-capsoils.

Asecondquestionis:What is the relationship between ash-cap soil properties and soil performance?Themajorityofresearchtodatehasfocusedonmeasure-mentofash-cappropertiesratherthanperformance.Forexample,compactionofash-capsoilshasbeenwelldocumented,butcompactedbulkdensitiesaretypicallywellwithintherangeconsideredtobeacceptableforothermineralsoils.Sowithregardtoperformance,doesanashcapwithbulkdensity1.1gcm3be-havedifferentlythanasoilwithoutanashcaphavingthesamebulkdensity?Ananswertothisquestionwillrequireabetterunderstandingofthechangesinporesizeandconnectivitythatoccurwithcompactioninash-capsoils.Effortsshouldbefocusedondeterminingcriticalthresholdsinandicsoilpropertiesatwhichtreegrowthandthehydrologicperformancewillbeadverselyaffected.Long-termstudieswillbeneededtoaddresstheseissues,andsuccessfulmanagementwillultimatelyrequireanunderstandingofthemechanismsinvolved.

References ______________________________________________________Arnalds,O.;Gisladottir,F.O.;Sigurjonsson,H.2001.SandydesertsofIceland.J.AridEnviron-

ments.47:359-371.Bacon,C.R.1983.EruptivehistoryofMountMazamaandCraterLakecaldera,CascadeRange,

USA.J.Volcanol.Geotherm.Res.18:57-115.



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Dahlgren,R.A.;Saigusa,M.;Ugolini,F.C.2004.Thenature,properties,andmanagementofvolcanicsoils.In:Sparks,D.L.,ed.AdvancesinAgronomy,vol.82.Amsterdam:ElsevierAca-demicPress:113-182.

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Geist,J.M.;Cochran,P.H.1991.Influencesofvolcanicashandpumicedepositiononproductiv-ityofwesterninteriorforestsoils.In:Managementandproductivityofwestern-montaneforestsoils:proceedings;1990April10-12;Ogden,UT:U.S.DepartmentofAgriculture,ForestService,IntermountainResearchStation:82-88.

Harsh,J.;Chorover,J.;Nizeyimana,E.2002.Allophaneandimogolite.In:Dixon,J.B.;Schultze,D.G.,eds.Soilmineralogywithenvironmentalapplications.BookSeriesno.7.Madison,WI:SoilScienceSocietyofAmerica:291-322.

Jimenez, J.2005.Bracken ferncommunitiesof theGrandFirMosaic:Biomassallocationandinfluenceonselectedsoilproperties.Moscow,ID:UniversityofIdaho.209p.Thesis.

Johnson-Maynard,J.L.;McDaniel,P.A.;Ferguson,D.E.;Falen,A.L.1997.Chemicalandmin-eralogicalconversionofAndisolsfollowinginvasionbybrackenfern.SoilSci.Soc.Am.J.61:549-555.

Jones,J.P.;Singh,B.B.;Fosberg,M.A.;Falen,A.L.1979.Physical,chemical,andmineralogicalcharacteristicsofsoilsfromvolcanicashinnorthernIdaho:II.Phosphorussorption.SoilSci.Soc.Am.J.43:547-552.

Kimble, J. J.;Ping,C.L.;Sumner,M.E.;Wilding,L.P.2000.Andisols. In:Sumner,M.E.,ed.HandbookofSoilScience.BocaRaton,Florida:CRCPress:E-209-224.

Kimsey,M.;McDaniel,P.;Strawn,D.;Moore, J.2005.Fateofappliedsulfateinvolcanicash-influencedforestsoils.SoilSci.Soc.Am.J.69:1507-1515.

Malla,P.B.2002.Vermiculites.In:Dixon,J.B.;Schultze,D.G.,eds.Soilmineralogywithen-vironmentalapplications.BookSeriesno.7.Madison,WI:SoilScienceSocietyofAmerica:501-529.

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McDaniel,P.A.;Falen,A.L.;Fosberg,M.A.1997.Genesisofnon-allophanicEhorizonsintephra-influencedSpodosols.SoilSci.Soc.Am.J.61:211-217.

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Nanzyo, M.; Dahlgren, R.; Shoji, S. 1993a. Chemical characteristics of volcanic ash soils.In:Shoji,S.;Nanzyo,M.;Dahlgren,R., eds.Volcanic ash soils—Genesis, properties, andutilization.Amsterdam:Elsevier:145-187.

Nanzyo,M.;Shoji,S.;Dahlgren,R.1993b.Physicalcharacteristicsofvolcanicashsoils.In:Shoji,S.;Nanzyo, M.; Dahlgren, R., eds. Volcanic ash soils — Genesis, properties, and utilization.Amsterdam:Elsevier:189-207.

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Terry L. Craigg, Soil Scientist, Deschutes National Forest, Sisters OR. Steven W. Howes, Regional Soil Scientist, U.S. Department of Agriculture, Forest Service, Pacific Northwest Region, Portland, OR.

AbstractForestmanagersmustunderstandhowchangesinsoilqualityresultingfromprojectimplementationaffectlong-termproductivityandwatershedhealth.Volcanicashsoilshaveuniquepropertiesthataffecttheirqualityandfunction;andwhichmaywarrantsoilqualitystandardsandassessmenttech-niquesthataredifferentfromothersoils.Wediscusstheconceptofsoilqualityandhowitmaybealteredbyactivity-inducedsoildisturbances.Apracticalapplicationoftheuseofsoildisturbancecategoriesandphysicalsoilindicesusedtoperformoperationalsoilmonitoringonanashcapsoilisalsodiscussed.

Introduction

Soil disturbance resulting from forest management activities is of concern to both landmanagersandthepublic.OnNationalForestSystemlandsintheNorthwestmanycurrentprojectsarebeingadministrativelyappealedorlitigatedbasedontheassumptiontheywillresultinsoildegradation.Someclaimthatwhenimplementinggrounddisturbingactivities,theForestServicecommonlyexceedsitsownstandardsintendedtomaintainsoilquality.There is aneed forobjectiveandaccuratemeasuresof change in soilqualitycausedbymanagementactivities.Assessingchange in soilquality isdifficult andcanbe influencedby a number of complicating factors. Properties of volcanic ash soils may also requiredevelopment and application of unique soil quality standards and assessment protocols.

Properties of Volcanic Ash Soils that May Affect Quality and Function

Many soils in the Inland Northwest have been influenced by ashfall deposits from theeruptionofMt.Mazama(nowCraterLake)aswellasotherCascadevolcanoes(HarwardandYoungblood1969).ThesedepositsarefoundinmostsoilsoftheColumbiaPlateauofcentralandeasternOregonandWashington.Soilsrangeintexturefrom“popcornpumice”

Assessing Quality in Volcanic Ash SoilsTerry L. Craigg and Steven W. Howes


Craigg and Howes Assessing Quality in Volcanic Ash Soils

nearCraterLaketosandsandsiltsasdistancefromsourceincreases.Volcanicashsoilshavephysicalandchemicalpropertiesthataffecttheirqualityandfunction;andthatmakethemuniquewhencomparedtoothersoilparentmaterials.

AstudyconductedbyGeistandStrickler(1978)comparedsomephysicalandchemicalpropertiesofvolcanicashsoilstoresidualsoilsderivedfrombasaltintheBlueMountainsofnortheasternOregon.Insummary,volcanicashsoilshad:

• Lowerbulkdensity • Higherporosity • Weakerstructuraldevelopment • Lowercohesion • Lowercoarsefragment(>2mm)content

SuchpropertiesaredescribedindetailbyothersintheseProceedings.Thispaperfocusesonsoilswithadistinct“ashcap”orsurfacelayerofvolca-

nicashdeposits.Suchdepositsvaryfromafewcentimeterstooverameterindepthdependingondistance fromthesource, topography,windpatternsandsubsequenterosion.

Volcanicashsoilshavearelativelyuniformundisturbedsurfacesoilbulkden-sity(0.67)andadisproportionateconcentrationofnutrients(totalOM,N,K)intheupper30cmofthesoilprofile.Thesepropertiestendtomakevolcanicashsoilsmoresusceptibletosurface(sheet,rill,wind)erosionwhenexposed;andtodisplacementbyground-basedequipment.Theystoremorewaterbutyieldalargerproportionofitinthelowsuctionranges.Volcanicashsoilsalsoseemtocompacttothesamedegreeoverawide-rangeofmoisturecontents.

Pumicesoilshavemanyof thesamepropertiesasothervolcanicashsoils.Likeothervolcanicashsoilsthelowdensity,lackofcohesion,andconcentra-tionofsoilnutrientsintheuppersoilprofileofpumicesoils,makepumicesoilssusceptibletosoilcompactionandthelossofnutrientsthroughsoildisplacement.Becauseoftheirlowcohesionbetweenindividualpumiceparticles,compactioninpumicesoilscanresultfrombothcompressionandvibration.Pumicesoilsalsohavebeenfoundtobemostsusceptibletocompactionwhentheyareverydryoratornearsaturation.Soilmoisturecontentsbetweenthesetwoextremesap-peartoprovidesomecohesionbetweensoilparticlesreducingsusceptibilitytocompaction.Amountsofsoilorganicmatterisalsoimportantwhendeterminingtheirsusceptibilitytocompaction.

Whencompactiondoesoccur,soilstrength(asmeasuredbyresistancetopen-etration)hasbeenfoundtoincreaseexponentiallywithanincreaseinsoilbulkdensity(Chitwood1994).Incompactedsoilssoilstrengthhasalsobeenshowntoincreasequicklyasthesoildriesoutoverthegrowingseason(Craigg2006).Thusmeasurementsofsoilstrengthandsoilbulkdensityareprovidingdifferentinformationaboutchangesoccurringinthesoilwhencompactionoccurs.Sincethereisnotasimplelinearrelationshipbetweenmeasurementsofsoilstrengthandsoilbulkdensitywhensoilconditionschangeitwouldbedifficulttoreadilysubstituteonemeasurementfortheother.

Considerationoftheseproperties,alongwithash/pumicedepthandunderlyingsoilmaterial, is important indeveloping soilmanagementobjectives/prescrip-tions,inevaluatingpotentialimpactsofproposedactivities,andinestablishingmeaningfulsoilqualitystandards.


Assessing Quality in Volcanic Ash Soils Craigg and Howes

Soil Disturbance and its Relationship to Soil Quality ________________Definitionsofsoilqualitydiffergreatlydependingonwhomoneasks.Most

wouldsaytheyrecognizeahighqualitysoil“when they see it”butwhenaskedtodefinesoilquality,eachwouldmostlikelyprovideadifferentanswerdependingontheirindividualobjectivesandpersonalbiases(Karlenandothers1997).Thequalityofanindividualsoilmayvaryfordifferingpurposes:ahighqualitysoilforproductionoftreesorforagemayhavelowqualityforproductionofcottonorwheat.Tosaythatonesoilisofhigherqualityor“better”thananotherisnotproperwithoutqualification.

Therearesomewhousetheterms“soilquality”and“soilhealth”interchange-ably(Warkentin1995).Eachsoilhasinherentphysical,chemical,andbiologicalpropertiesthataffectitsabilitytofunction asamediumforplantgrowth,toregulateandpartitionwaterflow,ortoserveasaneffectiveenvironmentalfilter.Whenanyoracombinationoftheseinherentfactorsisalteredtoapointwhereasoilcannolongerfunctionatitsmaximumpotentialforanyofthesepurposes,thenitsqualityorhealthissaidtobereducedorimpaired(LarsonandPierce1991).

Manyfactorsenterintomakingdeterminationsofsoilquality.Someofthesefactorscanbechangedbydisturbance (LarsonandPierce1991;Seyboldandothers1997;Grossmanandothers2001).Alterationofsoilproperties throughdisturbancemechanismsisnotnecessarilyharmful.Tillageisanextremeformofsoildisturbanceoftenusedtoimprovesoilqualityor“tilth”forproductionofagriculturalcrops.Inforestryapplications,sitepreparationtoimproveregenera-tionsuccessorsoilrestorationworkofteninvolvesoildisturbancetosomedegree(surface soilexposure, scalping, subsoiling).What sets theseapart fromotherformsofsoildisturbanceisthattheyareplannedandare,orshouldbe,carriedoutwithspecificobjectivesinmindunderprescribedconditions.

Managementactivitiesonforestandrangelandsoftenresultinvariousformsofdisturbancethatcanaltersoilfunction.Commonly,landmanagersareconcernedabouthowchangesinsoilqualityorfunctionresultingfromunplanned,activity-induceddisturbanceaffectthelong-termproductivityandhydrologicresponseofwatersheds.Inwildlandsituations,concernusuallyfocusesondisturbance-relateddeparturesfromnaturalsoilconditions(consideredtobemaximumpotentialorbestpossibleconditions),occurringaseitherlegacyimpactsorthosecausedbycurrentmanagementactivities.Understandably,therearedifferencesofopinionamong soil scientists and landmanagers aboutwhenandwhere “significant”thresholdsarereached.Thisiscomplicatedbythefactthatsoilsdifferintheirabilitytoresistandrecoverfromdisturbanceeffects(Seyboldandothers1999).

Disturbance may have negative, neutral, or even positive effects on a soildependingonitsinherentproperties.Meaningfulsoildisturbancestandardsorobjectivesmustbebasedonmeasuredanddocumentedrelationshipsbetweenthedegreeofsoildisturbanceandsubsequenttreegrowth,forageyield,orsedi-mentproduction.Studiesdesignedtodeterminetheserelationshipsarecommonlycarriedoutaspartofcontrolledandreplicatedresearchprojects.Thepaucityofsuchinformationhascausedproblemsindeterminingthresholdlevelsfor,ordefiningwhen,detrimentalsoildisturbanceexists;andindetermininghowmuchdisturbancecanbetoleratedonagivenareaoflandbeforeunacceptablechangesinsoilfunction(productivepotentialorhydrologicresponse)occur.Givennaturalvariabilityofsoilpropertiesacross the landscape,asinglesetofstandards forassessingdetrimentaldisturbanceseemsinappropriate.



Defining Detrimental Soil Disturbance _____________________________Soildisturbanceexistsinanumberofforms.Inforest,range,andwatershed

managementapplications,itmostcommonlyoccursascompaction,displacement,andpuddlingresultingfromuseofground-basedharvestingandslashdisposalequipment.Theremovalofabovegroundorganicmatterisalsoaresultofthistypeofdisturbance.Soildisturbancecanalsooccurintheformofsheetandrillerosionorcharredsoilinintenselyburnedareas.

Effectsofsoildisturbanceonsiteproductivityorhydrologicfunctionofwa-tershedsisdependentonitsdegree,extent,distribution,andduration(Froehlich1976;SniderandMiller1985;Claytonandothers1987).Degree refers to theamountofchangeinaparticularsoilpropertysuchasporosity,bulkdensity,orstrengthandthedepthtowhichthatchangeoccurs.Extent referstotheamountoflandsurfaceoccupiedbythatchangeexpressedasapercentage of a specified area.Distributionofsoildisturbancewithinamanagementareamaylikelybemoreimportantthantheactualestimatedextent.Disturbancecanoccurassmallevenly-distributedpolygons,orinlargepolygonsinoneorafewlocations.Dura-tionisthelengthoftimedisturbanceeffectspersist.Forexample,compactioneffectshavebeenmeasuredover30yearsfollowingtimberharvestactivitiesonsomesoils(Froehlichandothers1985).

Degreeanddurationofeffectsarelargelydeterminedbyinherentsoilproper-tiesthatinfluenceresistanceto,andabilitytorecoverfrom,disturbance.Extent,distribution,and,insomeinstances,degreeofdisturbancecanbecontrolledbyimposingmanagementconstraintssuchaslimitingseasonofoperation,spacingofskidroadsandtrails,andnumberofequipmentpasses.

Achallengehasbeentoestablishmeaningfulsoilqualitystandardsgiventheinherentvariabilityofsoilsacrossthelandscape.Simplystatingasinglethresholdbeyondwhichdetrimentalsoilconditionsarethoughttoexistmaynotbeenough.Mostforestlandmanagersdonotwishtodamagetheirproductivebaseorcauseimpairedwatershedfunction.However,theyalsodonotwanttounnecessarilylimitmanagementopportunities.

Current Status and Needs ________________________________________Soilqualitycanbeimproved,maintained,ordegradedbyforestmanagement

activities.Inordertoidentifyandquantifysuchchanges,ascientificallyrigorousprotocolisrequired.Itmustquantifytypesandamountsofsoildisturbanceswithinaspecifiedarea;andidentifyareasofdisturbanceconsideredtobedetrimental.Protocolsmustbe:

• Statisticallyvalid • Relativelyeasytoimplement • Costeffective • Usableatdifferentscales • Abletodetermineifsoilqualityisbeingmaintained,improvedordegraded.

Numerousmethodsexistforsamplingsoildisturbanceinbothoperationalandresearchsettings.Methodsdifferwithrespecttosamplingobjectives,soilvariablesconsidered,andassessmentprotocols.Inconsistentapplicationofsoildisturbancemeasurementtechniquesacrossavarietyoflandownershipshasled,insomecases,tounreliableandincomparableresults.Moreeffectiveandefficient(cost,



utilityofdata) soildisturbanceassessmentandmonitoringprogramscouldbeachievedthroughuseofcommonsoildisturbanceclassdefinitionsandconsistentuseofstatisticallyreliablesamplingprotocols(Curranandothers2005).

Definedsoildisturbancecategoriesmustberelatedtophysicalindicesofsoilqualityanddocumentedchangesinvegetationgrowthorhydrologicfunction.Adeterminationneedstobemadeif,infactoratwhatpoint,thesedisturbancecat-egoriesrepresent“detrimental”changesinsoilfunction.Inordertoevaluateimpactsofforestmanagementactivitiesonsoilquality,threedistinctlevelsofinformationareneeded.Thefirsttwoarecommonlygeneratedthroughagencyorcompanysoilmonitoringprograms.Thelastoneisprimarilyaresearchfunction.

Initialassessmentscanbeassimpleasdeterminingifspecifiedsoilconserva-tionorbestmanagementpractices(BMP)havebeenimplementedasplannedorifcontractual/legalrequirementsrelatingtosoildisturbancehavebeenmet.Thisisoftenreferredtoascomplianceorimplementationmonitoring.

After the initial compliance monitoring, soil disturbance assessment andmonitoringprojectsarecommonlydonetoevaluateeffectivenessofmanagementpractices.Theseassessmentsevaluatepre-determined,usuallyprovisional,soildisturbancestandardsorobjectivesbasedonbestavailableknowledge.Thisiscommonlyreferredtoasoperationaloreffectivenessmonitoring.

Soildisturbancestandardsorobjectivesmustalsobe testedorvalidated todetermineiftheyresultinunacceptablereductionsinproductivityorwatershedfunction,areappropriateforlocalsiteconditions,orifadjustmentsareneeded.Thisprocess isusually referred toasvalidationmonitoring.Validation isbestaccomplishedinaresearchenvironmentundercarefullycontrolledconditions.Ideally, research would be completed before standards were developed andimplemented.

Cost-effectiveapproachesareneededforoperationalsoildisturbanceassess-ments or monitoring that provides statistically valid and scientifically relevantdata.Monitoringmustmeetspecifiedquality-controlstandardsandcontributetoregionalstrategicdatabasesrelatingtreegrowthorhydrologicfunctiontodefinedclassesofdisturbance.Ourcurrentabilitytocompareresultsfromoperationaland research studies requiresmore commonor standardized soil disturbancedefinitionsandassessmentprotocols.

Tobecost-effective,operationalsoildisturbancemonitoringprotocolsmustmeet several criteria. Protocols (1) must provide scientifically and technicallysoundinformation,(2)mustbereliable,pertinent,andobtainedwithminimuminvestments,(3)mustbeclearlycommunicatedandunderstoodbyallaffectedparties,and (4)mustbeconsistentlyandefficiently implemented (Curranandothers2005).

USDA Forest Service Approach to Operational Soil Monitoring _______InForestServiceRegion6,initialassessmentsofactivity-inducedchangesin

soilqualityaretypicallymadethroughastratificationprocessinwhichvisuallyrecognizablesoildisturbancecategoriesanddisturbancesthatcanbeeasilyde-tectedbyprobingthesoilaredescribedandquantifiedwithinanactivityarea.Thisiscommonlyaccomplishedusingapointgridsystemincombinationwithpointobservationsalongaseriesofrandomlyorientedtransects.ThisprocessisdescribedindetailbyHowesandothers(1983).

Morerecently,pointobservationsarebeingreplacedbyvisualsoildisturbancecategories, developed and used to describe areas with a combination of soil



disturbancesthatrepeatacrossanactivityareaandwhicharelikelylargeenoughinextentanddistributiontoaffectsoilfunction.Visualcategoriesalsoaccountforthefactthatvariousformsofdisturbancearenotmutuallyexclusive.Forex-ample,compactionanddisplacementoftenoccurtogether.AninterimprotocolofthisprocessthatisbasedonproceduresdescribedbyScottandothers(1979)iscurrentlybeingusedonnationalforestsintheBlueMountains.

Theprocessofquantifyingdifferentsoildisturbancecategoriesacrossaland-scapeprovidesarelativelyrapidandinexpensivemethodforquantifyingdiffer-enttypesofsoildisturbancesoverlargeacreagesandisrecognizedbytheFSasanessentialstepinthesoilassessmentprocess.This process, however, is often stopped at this point and the incorrect assumption made that any soil distur-bance is detrimental.

Toavoidthispotentialproblem,visualsoildisturbancecategoriesmustbefurtherevaluatedtodetermineiftheydo,infact,adequatelyrepresentdetrimentalsoilconditions.Thefirststepinevaluatingadisturbancecategoryistoidentifythesoilfunction(s)thatmaybenegativelyaffectedbyasoildisturbance.Forexample,ifsurfacesoilshavebeendisplaced,asoil’sabilitytosupplynutrientsmaybereduced.Incompactedskidroadsandlandings,changesinsoilresistancetorootpenetrationaswellasairandwatermovementinthesoilmaybethemostimpor-tantconsideration.Identificationofsoilfunction(s)affectedbydisturbanceallowsfortheselectionofthemostappropriatesoilindicatorswhichcanthenbeusedtoassessachangeintheabilityofthesoiltofunction.Caremustbetakenwhendevelopingandinterpretingsuchindices.Environmentalfactorssuchasmacro-andmicro-climatecanmaskchangesinsoilfunctionduetodisturbance.

Soilindicatorsorindicesaresoilparametersthatcanbequantitativelymea-suredusingstandardizedmethodsandcomparedbetweendisturbedandundis-turbedsites.OnNationalForestSystemlandsintheNorthwest,soildisturbanceisconsideredtobedetrimentalwhenasoilindexiseitherhigherorlowerthanadefinedthreshold.

Development and Application of Forest Service Soil Quality Standards ______________________________________________________

TheUSDAForestServiceisdirectedbylawtosustainproductivityatcurrentorenhancedlevelsandtoprotectandimprovethesoilsforwhichitisresponsible.Recognizingthisresponsibility,thePacificNorthwestRegion(R6)issuedaForestServiceManualSupplementdealingwithsoilproductivityprotection in1979.Ithasbeen revisedanumberof times since then (current versionFSM2520.R-6Supplement2500.98-1,EffectiveAugust24,1998).Thisdirectionspecifiesthresholdvalues(degree)forestimatingwhendetrimentalsoildisturbanceoccursandalsosetsarealimits(extent)fordetrimentalsoildisturbanceonanactivityareabasis.MostnationalforestswithinR6haveincorporatedthesevalues,withminormodifications,asstandardsintheirforestlandandresourcemanagementplans.OtherForestServiceRegionssubsequentlydevelopedsimilarpolicyanddirection (Powersandothers1998).Thresholds forestimatingdetrimentalsoilcompaction,displacement,puddling,andseverelyburnedsoilsweredevelopedbasedonapplicableresearchresultsavailableatthetime.

Standards emphasize both observable and measurable soil characteristicsthat field personnel can use to monitor effectiveness of activities in meeting



soilmanagementobjectives.Allformsofdetrimentalsoildisturbance,includingpermanentfeaturesofthetransportationsystemsuchasroadsandlandings,arelimitedinextenttonomorethan20percentofanactivityarea.Inactivityareasthatexceed thisextent limiteitherasaresultofpreviousorcurrentactivities,restorationplansmustbeinplacebeforenewprojectsareimplemented.These standards are applied to all soils regardless of their inherent properties and ability to resist or recover from disturbance. Theonly special considerationgivenvolcanicashsoilsisanallowable20percentincreaseinsoilbulkdensitybeforetheyareconsidereddetrimentallycompacted.Thereasonforthisistheirrelativelylowundisturbedbulkdensitieswhencomparedtosoilsdevelopedinotherparentmaterials.

Application of Operational Soil Monitoring Techniques _____________Thefollowingisanexampleoftheuseofanoperationalsoilmonitoringproce-

durethatwasusedtoevaluatetheeffectsofaforestthinningoperationonthesoilresource.Theprocedureillustratestheapplicationofsoildisturbancecategoriesandphysicalsoilindices.

Overview

Duringthewinterof2005,theSistersRangerDistrictoftheDeschutesNationalForest in central Oregon implemented a thinning project designed to reducehazardousfuelsinpinestandswithinthewildlandurbaninterface.ATimberjackcut-to-lengthharvesterandaTimberjackforwarderwereusedtoremovetrees12inchesindiameterandsmaller,resultinginastandwithirregulartreespacingofabout20x20ft.

Projectobjectivesincluded:

• ReduceriskofwildfiretothenearbycommunityofBlackButteRanch. • Promoteresidualtreegrowthandmovestandtowardlargerdiametertrees. • Produceabiomassproductthatcouldbeusedtohelpoffsetthecostofthe

thinningoperation.

ThinningoperationsoccurredduringFebruaryandMarchof2005.Duringmuchofthistime,thesurface2to4inchesofsoilwasfrozen.Therewere,however,timeswhentemperaturesroseandsoilsweremoistbutnotfrozen.Severalsnowstormsalsooccurredduringthisperiod,depositingfromafewinchestooverafootofsnow.Soilconditionswerefavorableformostofthetwomonthperiodduringwhichoperationsoccurred.

Soilfunctionspotentiallyaffectedbytheprojectincluded:

• Abilityofthesoiltosupplywaterandnutrientstoresidualtrees. • Abilityofthesoiltoabsorbandtransmitwater. • Ability of the soil to resist other detrimental soil impacts including

displacement,puddling,severeburning,andsurfaceerosion.

Mitigationmeasuresused to reducepotentiallydetrimental soil impacts in-cludedoperatingoverfrozenground,snow,andslash;useofharvestequipmentdesignedtohavelowgroundpressure;designatingspacingofequipmenttrails;andhandpilingslash.



Forestmanagerswishedtoknowifthesepracticeswereeffectiveinmeetingsoilqualityobjectivesonthisandothersimilarprojects.Inthiscase,managerswished toknow if soildisturbance resulting from theabovesuiteofpracticesexceeded20percentoftheactivityarea.Theyalsowishedtoknowifdifferentcategoriesofdisturbancecontaineddetrimentalsoilimpactsasdefinedin(FSM2520.R-6Supplement2500.98-1).

Project Area Soils

SoilsintheprojectareaweremappedaspartoftheSoilSurveyoftheUpperDeschutesRiverArea,Oregon(NRCS2002).TheyaredescribedastheSisters-Yapoahcomplex0-15percentslopes.Soilsareclassifiedas:

Sisterssoilseries–Ashyoverloamy,mixed,frigidHumicVitrixerandsYapoahsoilseries–Ashy-skeletal,frigidHumicVitrixerands

Harvester/Forwarder Transportation System

TheTimberjackcut-to-lengthharvesterusedinthisoperationwasequippedwithacuttingheadmountedona30footboom.Thisallowedtheharvestertocutandprocessmaterialswhilemakingparallelpassesacrosstheharvestunitataspacingofapproximately60feet.Harvestedmaterialsarepositionedsotheycanbereachedfromalternateharvestertrailsbytheforwardermachine.Thisresultsintwotypesoftrailswithintheharvestunit(1)thosethatbeendrivenacrossonlyonetimebytheharvester(ghosttrails)and(2)trailsthathavebeendrivenacrossbytheharvesterfollowedbytheforwarder(harvester-forwardertrails).Becausetreesarelimbedandtoppedatthetimeoffellingtherearenolandingswithintheharvestunit.Oncetheforwarderhascollectedharvestedmaterialstheyarepilednexttoahaulroadpriortoloadingonlogtrucks.

Description of Visual Soil Disturbance Categories

Acombinationofvisualobservationsandprobingofthesoilwithatilespadeormetalrodwasusedtoidentifyanddescribefourcategoriesofsoildisturbancewithinactivityareas.Thesecategoriesare:

Condition Class 1:Undisturbedstate,natural. • Noevidenceofpastequipmentoperation. • Nowheeltracksordepressionsevident. • Litteranddufflayersintact. • Nosoildisplacementevident.

Condition Class 2:Trailsusedbytheharvestermachineonly.Ghost trails. • TwotracktrailscreatedbyonepassofaTimberjack cut-to-lengthharvester. • Faintwheeltrackswithaslightdepressionevidentandare<4inchesdeep. • Litteranddufflayersintact. • Surface soil has not been displaced and shows minimal mixing with

subsoil.

Condition Class 3:Trailsusedbybothharvesterandforwarder. • TwotracktrailscreatedbyoneormorepassesofaTimberjackcut-to-length

harvesterandoneormorepassesofaTimberjackforwarder.



• Wheel tracksevidentandare4 to6 inchesdeepwith theexceptionofareaswhereoperatorwasabletolaydownenoughslashtomitigatesoilimpacts.

• Litteranddufflayersarepartiallyintactormissing.

Condition Class 4:Skidtrailsfrompreviousentries.Allwerere-usedduringcurrententry. • Oldskidtrailscreatedintheearlypartof20thcenturywhenselectivehar-

vestoccurred. • Trailsappeartohavehighlevelsofsoilcompactionacrosstheentiretrail. • Evidenceoftopsoilremoval.

Soil Functions Affected by Soil Disturbances

Based on visual observations described above, it was determined that soilcompactionwasthemostprevalentformofsoildisturbancewithintheharvestedarea.Whencompactionoccurs,therearealterationsofbasicsoilpropertiessuchassoildensity,totalporevolume,poresizedistribution,macroporecontinuity,andsoilstrength(GreacenandSands1980).Soilsvaryintheirsusceptibilitytocompaction(Seyboldandothers1999).Onceasoilbecomescompacted,theconditioncanpersistfordecades(Froehlichandothers1985).This,inturn,af-fectssoilfunction.

Anumberofresearchershavemeasuredreductionsinsiteproductivityattributedtosoilcompaction(Froehlichandothers1986;CochranandBrock1985;HelmsandHipken1986).Effectsofsoilcompactiononsiteproductivity,however,arenotuniversallynegative.Gomezandothers(2002)lookedatarangeofforestsoiltypesinCaliforniaandfoundcompactiontobedetrimental,neutral,orbeneficialdependingonsoiltextureandwaterregime.

Quantifying Visual Soil Disturbance within an Activity Area

Toassistwithquantifying theamountof soilcompaction,a recordingpen-etrometerwasusedtodeterminetheaveragewidthofcompactedsoilsacrossboththeghosttrailsandtheharvester-forwardertrails(figs.1and2).Athresholdlevelfortheincreasedsoilstrengthof2.5MPawasusedtoidentifycompactedareas.Soilstrengthsbeyondthislevelwereconsideredtobehighenoughtobegintoinhibitplantrootgrowth.Basedonresultsharvesterghosttrailswereinitiallyconsideredtoconsistoftwodetrimentallycompactedtracks,eachapproximatelythreefeetinwidth.Harvesterforwardertrailswereconsideredtoconsistoftwodetrimentallycompactedtracks,eachapproximatelyfourfeetwide.

Arandomlyorientedsquaregridwithonegridintersectioneverytwoacreswasnextoverlainontheactivityareaandusedtolocatesamplepointsfordetermin-ingarealextentofsoildisturbancecategories(fig.3).Ateachofthegridinter-sections,arandomlyoriented,100-fttransectwasestablished.Thefourdefineddisturbancecategoriesweremeasuredalongeachtransectandlengthsoccupiedbyeachcategoryrecorded.Ameanforeachcategorywasthencomputedfortheentireactivityarea.Samplinginthismannerensuredanunbiased,representativesample.Itwasdeterminedthat17percentoftheactivityareawasoccupiedbysoildisturbance(totalofcategories2-4).A95percentconfidenceintervalaroundthisestimatewascalculatedtobeplusorminus2percent.



Figure 1—Average soil resistance measured for the 10 to 2� cm soil depth. Measurements were made perpendicular to the harvester ghost trails.

Figure 2—Average soil resistance measured for the 10 to 2� cm soil depth. Measurements were made perpendicular to the harvester forwarder trails.

Use of Soil Indices to Interpret Visual Soil Disturbance Categories

ThreephysicalsoilindicesusedbytheForestServicetoassesschangesinsoilphysicalpropertiesattributedtocompactionareincreasesinsoilbulkdensity,increases in soil strength (resistance topenetration),andchanges in soilporesizedistribution.

Soil Bulk Density

Soilbulkdensityisdefinedasthemassperunitvolumeofsoilandrepresentstheratioofthemassofsolidstothetotalorbulkvolumeofthesoil(SoilSurveyStaff1996).ThedirectmeasurementofanincreaseinsoilbulkdensityfromsoilcompactionrequiresaminimumamountofsamplingequipmentandisthemostcommonlymademeasurementofsoilcompactionusedbytheForestService.Physical factors that affect soil bulk density and compactability include soil



Figure 3—Example of a pre-established grid (randomly oriented) with transects oriented along random azimuths.

particlesizesanddensity,organicmattercontent,andmineralogy(Howardandothers1981).

Soilbulkdensitysampleswerecollectedinthespringoftheyearusingaham-mer-drivensoilcoresampler.Table1showssoilbulkdensitiesreportedforboththewholesoilandfor thefinefractionofsoil (soilparticles<2mmremoved).DeterminingsoilBDbasedonthefinefractionofsoilresultsinalowerBDvaluecomparedtothatdeterminedonawholesoilbasis.Thisisduetothehigherweighttovolumeratioofsoilcoarsefragmentsinthesoilcore,comparedtoanequalvolumeofsoilmaterial.Whendeterminedonawholesoilbasis,soilcompactionresultedinasignificantincreaseinsoilbulkdensityinboththeghosttrailsandtheforwardertrails.Soilbulkdensitiesdeterminedforthefinefractionsofsoilweresignificantlygreaterintheforwardertrailsbutnotintheghosttrails.

Table 1—Soil bulk density measurements determined based on the whole soil (including soil coarse fragments >2mm) and based on the fine fraction of soil.

% Volume Soil Soil Bulk Density Soil Bulk DensitySoil Condition Class Coarse Fragments Whole Soil (Mg/m3) Fine Fraction Soil (Mg/m3)

1 1 0.9�a 0.92a 2 2 1.02b 1.00ab � 2 1.0�b 1.0�b Columns within a soil bulk density analysis method are not significant at p = 0.05 if followed by the same letter. n = 3



Inthiscase,fewcoarsefragmentswereencounteredandtherewaslittledif-ferenceinsoilBDbetweenresultsobtainedusingcoreswithandwithoutcoarsefragments.Iftherehadbeenmorecoarsefragmentsincoresoralargevariationincoarse fragmentsbetweencores, itwouldhavehadagreater influenceoncalculatedsoilbulkdensitiesandonthewayinwhichthesoilfunctions.Tocor-rectlyinterpretsoilbulkdensitymeasurements,itisnecessarytoreportsoilbulkdensitiesforwholesoilandthefinefractionofsoil.Itisalsonecessarytoknowtheamountsofcoarsefragmentsinthesoilcores.

ForestServicesoilqualitystandardsidentifyachangeinsoilbulkdensityof20percentormoreaboveundisturbedlevelsasathresholdfordeterminingdetrimentalcompactioninAndisols(soilsderivedfromvolcanicash).Whencalculatedonbothawholesoilandfinefractionofsoilbasis,nomeasuredincreasesinsoilbulkdensityexceededthe20percentrelativeincreasethreshold.Therefore,noneofthesoilbulkdensitychangesinanyofthevisualsoildisturbancecategoriesmettheForestServicedefinitionofadetrimentallycompactedsoiltable2.

Soil Strength

Soilstrengthdescribesthesoilhardnessorthesoilsresistancetopenetration.Soilprobesandspadescanbeusedtodetectchangesinsoilstrengthresultingfromsoilcompaction.Thistechniquecanbequantifiedbyusingarecordingsoilpenetrometer.Measuredsoilstrengthscanvarydependingonsoilparticlesizedistributionandshape,clayandorganicmattercontent(ByrdandCassel1980).Withinasoiltypechangesinsoilwatercontentandstructurecanalsoaffectsoilstrength(Gerard1965).

Changesinsoilstrengthresultingfromsoilcompactionweremeasuredwithindifferentdisturbancecategoriesusingarecordingsoilconepenetrometer,whichiscapableofrecording,atpredeterminedintervals, theforcerequiredtopushaconeintotheground(Millerandothers2001).Measurementsweremadeinearlyspring,shortlyafterharvestoperationswerecomplete.Fieldmeasurementsofgravimetricsoilmoisture,basedonthefinefractionofsoil,rangedfrom0.19to0.22g/gandwereslightlylessthanthe0.23g/gestimateofsoilfieldcapacitythatwasobtainedfromsoilcoresamplesusedtodeterminesoilporesizedistri-bution.Thepenetrometerwassettorecordsoilresistanceat1.5cmincrementsbetween0and60cmsoildepth.ReadingswerethendownloadedtoaMicrosoftExcelSpreadsheetforanalysis.

Table 2—Absolute and relative percentage increase in soil bulk density as a result of soil compaction.

Absolute Increase Relative % Soil Bulk Density Soil Bulk in Soil Bulk Increase in Soil Condition Class Determination Method Density (Mg/m3) Density (Mg/m3) Soil Bulk Density

1 Whole Soil 0.9� 2 Whole Soil 1.02 0.09 10 � Whole Soil 1.0� 0.1� 1�

1 Fine Fraction 0.92 2 Fine Fraction 1.00 0.0� 9 � Fine Fraction 1.0� 0.14 1�



Soiltextureandseasonalchangesinsoilmoisturecangreatlyinfluencesoilstrengthmeasurements.Resistancetopenetrationhasbeenshowntoincreaseforbothuncompactedandcompactedsoilsas theydryoutover thegrowingseason.Theincreaseinresistancetopenetrationwithdecreasingsoilmoisture,however,tendstooccurmorerapidlyincompactedsoilsthaninuncompactedsoils(Craigg2006).Therefore,soilmoisturerelationshipsshouldbeconsideredwheninterpretingsoilresistancemeasurements.

Measurementsofsoilresistanceintheundisturbedareasgraduallyincreasedwithsoildepthreachingaresistanceof1MPainthefirst10cmandafinalsoilresistanceof2MPaatapproximately60cmsoildepth.Intheforwardertrailssoilresistanceincreasedmuchfaster,reachingaresistanceof3MPawithinthefirst10cmsoildepthandretainingthathighstrengththroughoutthe60cmdepth.Increasesinsoilresistanceintheghosttrailswerehigherthantheundisturbedbutlessthantheforwardertrails(fig.4).Duringthethinningoperationeffortsweremadetolimbharvestedtreesontheequipmenttrailsandthendriveontheslashmattomitigatesoilcompaction.Soilpenetrometermeasurementsindicatedthattheslashmatdidhaveatleastsomeaffectonmitigatingsoilcompaction(fig.5).

Currently,ForestServiceRegion6doesnothaveasoilqualityindexthresh-oldforincreasesinsoilresistanceresultingfromcompaction.Researchresultssuggestthatsoilresistancesof2MPaandgreatercanbegintoaffectplantrootgrowth(Siegel-Issemandothers2005).Thustheseresultssuggestdifferencesinsoilfunctionbetweenthedifferentsoilconditionclasses,inparticulartheabilityofrootstopenetratecompactedsoils.

Figure 4—Soil strength measured in the spring of 200� for different soil disturbance classes. Horizontal bars indicate one standard error. n = 30.



Soil Pore Size Distribution

Soilporespaceaccountsforapproximatelyhalfofthetotalvolumeofmineralsoil.Changesintotalsoilporosityandporesizedistributionthatmayresultfromsoilcompactioncanaffectsoilfunctionsbyalteringairandwaterflowintoandthroughthesoil.Changesinsoilporositycanalsoaffecttheamountsofwaterstorageinthesoil(Scott2000).

Measuringafullrangeofsoilporesizesrequiresrelativelysophisticatedlabora-toryequipmentcomparedtothatneededformeasuringsoilbulkdensityorsoilstrength.Althoughtotalsoilporositycanbeestimatedfrombulkdensityandsoilparticledensity,thiscalculationprovidesnoinformationaboutporesizedistri-butionchangesoccurringinthesoil.Tobetterunderstandchangesinsoilporesizedistributionresultingfromsoilcompaction,arelativelysimplemethodwasusedwhichdoesnotrequiretheuseofsophisticatedlaboratoryequipment.Thistechniquemeasuresmainlytheporositychangesoccurringinthelargersoilporesizes(soilpores>30μm).

Intactsoilcoresformeasuringsoilporesizedistributionwerecollectedusingthesamehammer-drivencoresamplerusedtosamplesoilbulkdensity.Follow-ingcollectionofintactsoilcores,soilporesizedistributionwasdeterminedus-ingamodificationofthewaterdesorptionmethoddescribedin(DanielsonandSutherland1986).Briefly,ahangingwatercolumnwascreatedbyconnectingaBuchnerfunnelwithaporousceramicplateinthebottomtoapproximately3metersofplastictubingwithaburetteconnectedtotheotherend.Asoilcorewas thenplaced in the funnelandsaturatedwithwaterbyraising theburette

Figure 5—Soil strength measured in the spring of 200� for different soil dis-turbance classes with measurements on harvester forwarder trails separated depending upon whether or not slash was present. Horizontal bars indicate one standard error. n = 30 (undisturbed and ghost trails)n = 15 (forwarder trails)



andcreatingaslightheadofwater.Aseriesofsuctionswerenextappliedtothesaturatedsoilcorebyraisingthefunnelaboveapredeterminedmarkonthebu-rette.Volumesofwaterremovedfromthesoilcoreswererecordedforaseriesofappliedsuctionsandtheequivalentradiusofthelargestsoilporesfilledwithwaterdeterminedbythecapillaryequation(Scott2000).

Resultsindicatedashiftinsoilporesizedistributionfromlargerporesizesormacropores(soilpores>30μm)tosmallerporesizes(soilpores<30μm)whensoilsbecamecompacted(fig.6).Whilesoilcompactiondidresultinasignificantdecreaseinmacroporesandasignificantincreaseinsmallersoilporesizes,therewasnotasignificantchangeintotalsoilporositybetweenthedifferentdisturbancecategories(table3).AlthoughstandardshavebeenestablishedinForestServiceRegion6formacroporespacereductionsinresidualsoils,nonehaveyetbeenestablishedforash-derivedsoils.

Figure 6—Shift in soil pore size distributions for different soil disturbance classes following soil compaction.

Table 3—Changes in soil pore size distribution and total soil porosity resulting from soil compaction.

Pore volume Pore volume Total pore volumeSoil condition Class >30µm (cm3/cm3) <30µm (cm3/cm3) (cm3/cm3)

1 0.��a 0.24a 0.�9a 2 0.29b 0.27b 0.��a � 0.2�b 0.�0c 0.��a n = 3 Columns within a pore size class are not significant at p = 0.05 if followed by the same letter.



Interpretation of Results

Extentofsoildisturbancewithintheprojectareawasinitiallydeterminedbyfirstdescribingandquantifyingvisualsoildisturbancecategoriesandthenmea-suringasuiteofindiceswithineachcategory.Soilindexmeasurementsthatweremadewithindisturbedareaswerethencomparedtothosemeasurementsmadeinundisturbedareas.Degreeofchangeinspecifiedsoilindiceswasnextcomparedtodefinedthresholdsfordeterminingifthechangeisconsidered“detrimental”or“undesirable.”

AllmeasuredincreasesinsoilbulkdensitywerebelowthresholdvaluesdefinedbythePacificNorthwestRegionforsoilsderivedfromvolcanicash.Althoughin-creasesinsoilstrengthweremeasuredforghosttrailsandforharvester-forwardertrails,nothresholdvalueorsoilqualitystandardhasyetbeenestablishedinthePacificNorthwestRegionforsoilstrength.Reductionsinmacroporespacewerealsomeasured in ghost trails and forharvester-forwarder trails. Forest ServiceRegion6doesnotcurrentlyhaveasoilqualityindexthresholdestablishedformacroporespacereductionsinash-derivedsoils.Soilstrengthandreductionsinmacroporespaceappeartobereliableandeasilymeasurableindicesofsoilfunc-tion.Theyalsoprovideadditionalinformationaboutchangesoccurringinthesoilwhencompactionoccurs.Validationworkneedstobecompletedtodetermineappropriatethresholdsforeachoftheseindices.

Summary ______________________________________________________Soilqualitycanbedefined inanumberofwaysdependingonone’spoint

of view. For forest practitioners, management-induced changes in soil qualityareofconcernwhensiteproductivity ismeasurably reducedorwaterqualityisimpaired.Soildisturbancecanbeaccuratelydescribedandquantifiedusingconsistentvisualcategoriesandsound,cost-effectivesamplingprotocols.Assess-mentsofsoilqualitymustrelatevisualdisturbancecategoriestochangesintheabilityofthesoiltoprovidenutrientsortoabsorbandtransmitwater.Anumberofphysicalsoilindices(soilbulkdensity,soilstrength,soilporesizedistribution)areavailabletohelpdefinesuchrelationships.

Soilsvaryacrossthelandscapeandresponddifferentlytomanagementprac-tices.Caremustbetakenwhenmakingsoilqualityassessmentstoselectthemostappropriate soil indices, to followproper samplingprotocols, and to interpretresultscorrectly.Finally,withoutknowingeffectsofsoildisturbanceonsitepro-ductivityandsedimentyield,meaningfulassessmentsofsoilqualitycannotbemade.Validationofsuchcauseandeffectrelationshipsisastepintheprocessthatisoftennevercompleted.

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Timberjack cut-to-length harvester

Timberjack forwarder machine



Harvester forwarder trail

Quantification of soil disturbance categories using randomly oriented 100 foot transects.



Measuringsoilresistanceusingtherecordingsoilpenetrometer.

Past Activities and Their Consequences on Ash-cap Soils



Leonard R. Johnson and Han-Sup Han are faculty in the area of forest operations in the College of Natural Resources at the University of Idaho. Debbie Page-Dumroese is a Research Scientist with the Rocky Mountain Research Station, U.S. Department of Agriculture, Forest Service and is based in Moscow, Idaho.

Abstract Withpressureandvibrationonasoil,airspacesbetweensoilparticlescanbereducedbydisplacedsoilparticles.Activityassociatedwithheavymachinetrafficincreasesthedensityofthesoilandcanalsoincreasetheresistanceofthesoiltopenetration.Thispaperreviewsresearchrelatedtodisturbanceofforestsoilswithaprimaryfocusoncompactioninash-capsoils.Thegeneralprocessofcompac-tionisdescribedalongwithphysicalpropertiesofash-capsoilsthatrelatetocompaction.Ash-capsoilshavephysicalsoilpropertiesmostcloselyalignedtosilt-loamsoils.Undisturbedash-capsoilsoftenhavelowbulkdensitiestovariabledepths.Undermoistureconditionsnearfieldcapacity,thesesoilsaresusceptibletosignificantdisturbancefrommachinetraffic,andwhenthedisturbancecausesincreasesinbulkdensity,thesoilsarenotlikelytorecoverfromthisdisturbedconditionformanyyears.Machinetrafficonforestsoilsgenerallyoccursasaresultofsomeformofactivestandmanage-mentincludingprecommercialthinning,intermediateandfinaltimberharvest,andsitepreparationactivitiesinvolvingslashdisposalandtreatment.Thedirectcontactbetweenequipmentandtheforestsoilwillresultinsometypeofsoildisturbance.Thedegreeandextentofthesoildisturbanceismostoftencontrolledthroughguidelinesontheselectionandoperationofequipmentandbyrestrictingthelocationandoperatingseasonforequipment.

Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils

Leonard R. Johnson, Debbie Page-Dumroese and Han-Sup Han

Introduction

General Process of Compaction

Compactionofsoilsiscreatedthroughtheenergyexertedonthesoil,usuallythroughvehiculartrafficinharvestingandsitepreparationoperations.Itresultsinthereductionofairspacesinthesoilwithacorrespondingincreaseinthebulkdensityofthesoil(weightperunitofvolume).Erosioncanalsoresultfromforestoperations.Erosiongenerallyoccursasaresultofsoildisplace-mentandismostoftenassociatedwithharvestandsitepreparationactivitiesonsteeperslopes. Althoughgenerallyviewedinanegativecontextwithrespecttoforestsoils,compactionisoftenadesirableprocessinconstructionactivities.Manyengineeringprojectsinvolvingearthworkinearthendams,structuralfoundations,androadsrequirepredictablestrengthinthesoilsthatareat


Johnson, Page-Dumroese and Han Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils

thefoundationoftheconstructionprojects.Variouscompactionmethodshavebeendevelopedtoachieveadesiredlevelofsoilstrengthanddensity.Someoftheprinciplesderivedfromresearchincivilengineeringandsoilmechanicsonachievingdesiredlevelsofcompactioncanalsobeappliedtoforestsoilsinde-terminingconditionswherenaturalsoilsareatthegreatestriskofcompaction.CullenandMontagne(1981)conductedanextensivesummaryofliteratureonthegeneralrelationshipsbetweensoilpropertiesandcompaction.Theirreviewincludesthegeneralrelationshipbetweenthesoilpropertiesoftexture,fragmentcontent,structure,moisturecontentatthetimeofcompaction,andorganicmatterandthesusceptibilityofthesoiltocompaction.AmorerecentreviewbyMillerandothers(2004)summarizedcurrentliteratureontheeffectsofheavyequip-mentonsoilsandproductivity.Thediscussioninthissectiondrawsheavilyontheseliteraturereviews.

Engineering Compaction Methods

Compressionorkneadingcompactionisgenerallyachievedinthefieldwithequipmentthatexertsgraduallyincreasingpressureonthesoil.Pressureisgradu-allyincreasedtoamaximumandthenisgraduallydecreased.Adevicecommonlyusedtoaccomplishthistaskinconstructioniscalledasheepsfootroller.Rubbertiredrollersalsoexhibitthecharacteristicsofthiskneadingaction.Theinteractionofthetiresofrubber-tiredskiddersusedinforestoperationswiththesoilseemstoresemble thatofkneadingcompactionmachines,butwith far lesspressurethantheequipmentdesignedforthatpurpose.

Vibratory compactors usually combine pressure on the soil with vibration.Hand-heldmodelsutilizeavibratingplate.Largerversionscombinealargesteelrollerwithavibratoryimpulse.Thereissomeconjecturethattrackedequipmentusedinforestoperationscanduplicatethisaction,but,again,withfarlesscom-pactiveenergythanequipmentdesignedforthatpurpose.

Engineeringproperties of soils are important to compaction. In addition tomoisturecontent,importantfactorsincludeinitialsoilstrengthorbulkdensity,distributionofparticlesizes,percentorganicmatter,rock-fragmentcontent,andpercentsand,siltorclay(soiltexture).Thepresenceandinfluenceofclayinthesoilwillusuallydeterminewhetheritisclassifiedascohesiveornon-cohesive.Clayinfluencesthesusceptibilityofsoilstocompactionbecauseofthesmallparticlesizesofclay,claymineralogy,andthroughitseffectonshearstrength.Withsmallclayparticles,theshearstrengthonsoilscanbepartiallyattributedtothechemicalbondingandelectro-chemicalresistancebetweenparticles(Brown1977).

Soiltype,textureandstructurewillinfluencetheequipmentthatismostef-fectiveinachievingthehighestlevelofcompaction.MeansandParcher(1963)foundthat“maximumdensitiesforsoilswithcoarsetexturewereachievedwitha heavy smooth-wheeled rollerwith somevibratory effects.”Coarse texturedsoils,usuallythoseverylowinclaycontent,arenon-cohesiveandthesegenerallyrequirevibratorycompactors.Fine-texturedsoilsandsoilswithahighcontentofclayareusuallynotcompactedwellthroughvibratorycompactorsandrequirethekneadingactionofamechanismsimilartoasheepsfootroller(Ingersoll-Rand1975).Kryine(1951)notedthat,ingeneral,themaximumsoildensitiesachievedbyseveralmethodsoflaboratoryandfieldcompactiondecreasewithdecreasingsoilparticlesize.Thehighestdensitiesgenerallyoccurinsoilswithawiderangeinparticlesizeswhereparticlescanbereorientedinwaysthatallowthesmall


Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils Johnson, Page-Dumroese and Han

particlestopackintothevoidsbetweenthelargerparticles(Li1956;CullenandMontagne1981;Millerandothers2004).

Ash-capsoilshaveuniquecharacteristicsthataffecttheirresponsetothevariouscompactionmethods.Whiletheparticlesizeisrelativelysmall,ash-capsoilsarealsoconsiderednon-cohesiveandnon-plastic(Cullenandothers1991).Becauseoftheirnon-cohesivenature,theyarelikelytobesusceptibletovibratorycom-paction(CullenandMontagne1981).Whilethekneadingactionofasheepsfootrollerwouldprobablyexceedtheshearstrengthofash-capsoilsandwouldnotbeeffectiveforcompaction,thepressureandmoresubtlekneadingactionproducedbyrubber-tiredandtrackedvehiclescouldincreasebulkdensities.

Froehlich and others (1980) completed a general report for the EquipmentDevelopmentCenteroftheU.S.ForestServicetoprovideabasisforpredictingsoilcompactiononforestedland.Observedsoiltypesincludedsandyloam,clayloamandloam.Thestudydevelopedequationstopredictabsoluteandpercentchangesinbulkdensitywithvehiculartraffic.Whilespecificvaluesassociatedwiththeequationsmaynotbeusefulinabroadsense,thestatisticallysignificantfactorsareofinterest.Theseincludethenumberoftripsbyequipment,initialsoilstrength(coneindex),initialsoildensity,machinederivedpressureofthevehicleinkilogramspersquarecentimeter,soilorganicmatterinpercent,soilmoisturecontentinpercent,andforestfloordepth.Themostsignificantofthesefactorswerenumberoftripsandtheinitialconeindexofthesoil,reflectingameasureofinitialsoilstrengthandthelevelofmachineactivityastwoprimaryfactorsindeterminingchangesinsoilcharacteristics.

Optimum Moisture Content

Theoptimummoisturecontentforcompactionisrelatedtotheenergygeneratedinthecompactioneffort.Ascompactioneffortincreases,soilswillbecompactedtohighersoilstrengthandbulkdensity.Themaximumbulkdensitywillalsooccuratloweroptimummoisturecontent.Soilsbelowtheoptimummoisturecontentwillnotbecompactedtoashighabulkdensityaswhentheyareattheoptimummoisturecontent(HåkanssonandLipiec2000).Uptoandincludingtheoptimummoisturecontent,watercanlubricateparticlesandallowtheirreorientationwithrespecttoeachother.Mostcompactionisseeninwetconditions,particularlynearsoilfieldmoisturecapacity(AlexanderandPoff1985).Whensoilmoistureexceedstheoptimummoisturecontentofthesoil,soilsbegintobecomeplasticortheincompressibilityofthewaterpreventsreorientationandpackingofthesoilparticles.AccordingtothereviewbyCullenandMontagne(1981),optimummoisturecontentforcompactiontendstoincreaseassoiltexturebecomesfiner(Felt1965).Thelessdensetheinitialsoilsample,thegreaterthemoisturecon-tentrequiredtoreachmaximumsoildensityforagivencompactiveeffort(Lull1959).

Optimum moisture content for compaction is determined for engineeringpurposesbyalaboratoryanalysiscalledtheProctortest.Thestandardproctortestinvolves25blowsofa2.5kghammerdroppedfromaheightof30.5cm.Becausethistestdidnotgeneratesufficientenergytopredictcompactioneffortsofmostmodernconstructionequipment,amodifiedproctortestwasdeveloped.Themodifiedtestincreasedthecompactionenergy,using25blowsofa4.5kghammerdroppedfromaheightof45.7cm.BoththestandardandmodifiedProc-tortestscreatedtoomuchcompactionenergytoeffectivelypredictcompaction



fromequipmentusedinforestoperations(Froehlichandothers1980).Alightproctortestusing8%oftheenergyofthestandardProctortestappearedtobeeffectiveinpredictingthecompactioneffortofharvestingandsitepreparationequipment.Itinvolved10blowsofahammerweighing0.5kgdroppedfromaheightof30.5cm.Thegeneralrelationshipbetweenoptimummoisturecontent,maximumbulkdensityandlevelofcompactioneffortareillustratedinFigure1.Ascompactionenergyincreases,theoptimummoisturecontentforcompactiondecreases.

Soiltexturecanalsoaffecttheresponseofthesoiltocompactioneffortsanditssensitivity tomoisturecontent.Figure2 illustrates theoreticaldifferences inmaximumbulkdensityandsensitivitytomoistureforwellgradedanduniformsoilswhenotherfactorsofthesoilareheldconstant.AlthoughthelightProctortestcouldbeusedtopredictmaximumbulkdensitiesthatmightresultfromforestoperationsforsomesoiltypes,italsoshowedthatthesoilswerelesssensitivetomoisturecontentwhentherewaslesscompactionenergyapplied.Thecom-pactioncurvewasflatterand,insomecases,U-shapedasillustratedinFigure3(Froehlichandothers1980).

Davis(1992)usedthelightProctortestinhisstudiesofbulkdensitychangesintwocentralOregonsoils.Hefoundthelightproctortesttobeadequatefordescribingacobblyloamsoil,butfoundatestusingtheheavierhammerofthestandardproctortestwith5to10blowsofthehammer(ratherthan25)tobemoreaccurateinpredictingcompactionfortheash-capsoilwithsandyloamtexture.HisProctortestsshowedgraduallyincreasingbulkdensitiesascompactioneffortincreased,buttherewasnotahighsensitivitytosoilmoisturecontent.

Totalorganicmattercontentinthesoiliscloselyrelatedtoaggregatesizeandstability.Thusareductioninorganicmattercontentwillresultinalossofag-gregatestabilityandasubsequentincreaseinasoil’spotentialforcompaction(AlderferandMerkle1941).WorkingwithfoursoilsinNewYork,Freeandothers(1947)concludedthatsoilsamplescontainingthemostorganicmatterwouldbecompactedtheleastatgivenmoisturecontentsandcompactiveefforts.Thisre-lationshipbetweenorganicmatterandcompactibilityofsoilswasalsoconfirmedinthereviewconductedbyMillerandothers(2004).

Figure 1—General relationships between moisture content, compaction effort and maximum bulk density.



Methods and Limitations of Measuring Compaction ________________Thereareseveralmethodsavailabletomeasurecompaction,butallhavelimita-

tionsinforestsoils.Twoofthemostcommoninclude:(1)thebulkdensityofthesoiland(2)soilstrengthasoftenmeasuredbytheresistanceofthesoiltopenetrationwithacalibratedpenetrometer.Whilemeasurementofbulkdensityorsoilstrengthbeforeandaftervehiculartrafficisidealbecauseitreducessamplingerror,itissel-domdone.Mostoftenthemeasurementsaretaken“onandoff”compactedareas.Ifthesoildisturbancehasalsodisplacedsoilsincompactedareas,thisleadstotheriskofcomparingsoilcharacteristicsinonesoilhorizonwiththoseinanother.

Figure 3—Proctor test results on light soil gravelly sandy loam soil with initial bulk density near 0.70 g/cm� (Mg/m� ) and 2% clay content adapted from Froehlich and others (19�0).

Figure 2—General relationships of optimum moisture content and maximum bulk density for well graded and uniform textured soils.



Bulk Density

Bulkdensity,thedrymassofaunitvolumeofsoil(BlakeandHartge1986),iscommonlyusedtomeasuresoilcompaction.Bulkdensityandrockcontentmeasurementsarerequiredtoconvertsoilnutrient,water,andmicrobialmeasurestoamass-per-areabasistocomparebetweensiteswithdifferentbulkdensitiesandwithin-siteprocesses(McNabbandothers1986).Althoughrocksareoftennotalargecomponentofash-capsoils,rootsandsteepslopesmakeitextremelydifficulttoaccuratelydeterminesoilbulkdensity.Anumberofdifferentmeth-odshavebeenusedtodeterminebulkdensityinsoils.Thesecangenerallybecategorizedas(1)coresampling,(2)excavationandvolumedisplacementand(3)radiation.

Core samplingisasimple,straightforwardmethodformeasuringbulkdensity.Cylindersofaknownvolumearedrivenintothesoilandtheresultantsoilcoredriedandweighed.Insomecases,narrowandsmallcoresamplersmayover-estimatebulkdensitybycompactingsoilintothecylinderwhenitishammeredintothesoil.

Volume excavationisanappealingalternativetocoretechniquesbecauseitallowsforflexibilityinvolumeofsoilsampledbasedonthesizeofsoilcoarse-fragments,rootsorhardpans.Aholeisexcavatedtothedesireddepthandwidth,allsoilmaterialisremovedandcollectedforweightdeterminationandthevol-umeoftheholemeasured.Variousmethodshavebeenusedtomeasureholevolumeincludingknownquantitiesofsandorstyrofoamballs,waterasmeasuredinaplasticbagliningthehole(Kohl1988),andexpandingpolyurethanefoam(Page-Dumroeseandothers1999).

Radiation methodsareinstantaneous,produceminimalsoildisturbance,allowaccessibilitytosubsoilmeasurementswithoutexcavation,donothavetobeonalevelsite,andhavetheoptionofcontinuousorrepeatedmeasurementsofthesamepoint(BlakeandHartge1986).Withanuclearmoisture-densitygauge,thesourceprobe is lowered toselectedsoildepths throughaccess tubesand theaveragedensitybetween thesourceandsurface-locateddetector isobtained.However,usinganucleargaugeisnotcommononforestsitesfarfromaroadsinceitweighsabout18kg.Inaddition,theequipmentoperatormuchbecertifiedtohandleandtransportradioactivematerial(FlintandChilds1984).

Penetrometer

Soilpenetrabilityisameasureoftheeasewithwhichaprobecanbepushedordrivenintothesoil(Vazandothers2001).Theresistancetopenetrationisre-latedtothepressurerequiredtoformasphericalcavityinthesoil,largeenoughtoaccommodatetheconeof thepenetrometer,andallowingfor thefrictionalresistancebetweentheconeanditssurroundingsoil.Easeofpenetrationbytheprobeisinfluencedbybothsoilandprobecharacteristics.Soil-to-probefrictionisgovernedbyprobefactorssuchasconeangle,diameter,roughnessandrateofpenetration.Soilfactorsinfluencingpenetrationresistancearematricwaterpo-tential(watercontent),bulkdensity,soilcompressibility,soiltexture,andorganicmattercontent(Smithandothers1997;Vazandothers2001).

Majorfactorsthatlimittheuseandinterpretationofpenetrometersasfieldindi-catorsofexcessivecompactionaretheinfluencesofwatercontentandinitialbulkdensity,mostlybecausethereisaninsufficientdatabasetoallowadjustmentsfor



thesefactors(GuptaandAllmara1987;BennieandBurger1988).Awidelyacceptedmethodistomeasurepenetrometerresistanceatornearfieldmoisturecapacity.

Penetrometer-measuredsoilstrengthhasbeenprincipallylinkedwithsoilbulkdensity,watercontent,claycontent,andorganiccarbon.Usuallysoilstrengthincreaseswithincreasingbulkdensityanddecreasingwatercontent,exceptatlowerlevelsofcompactionwhensoilstrengthdeclinesassoilsdryout(Smithandothers1997).Sincesoilstrengthisstronglyrelatedtowatercontent,itvariesconsiderablythroughouttheyearwitheachwettinganddryingcycle(Busscherandothers1997).Thisrelationshipisalsoinfluencedbythedegreeofcompac-tion(MirrehandKetcheson1972).Increasingclaycontentsappearstoreducetherateatwhichsoilstrengthincreasesassoilsdrytowiltingpoint.Withincreasingorganicmattercontent,soilstrengthvaluesarehighatfieldcapacity,especiallyathigherbulkdensities(Smithandothers1997).

Correlation between methods of measuring compaction

Increasesinbulkdensitygenerallyhaveapositivecorrelationtoincreasesintheresistancetopenetrationasmeasuredbyapenetrometer,butspecific,statisticalrelationshipsbetweenthesetwotypesofmeasurementhavebeenmuchmoredifficulttoestablish.Effortstocorrelatebulkdensitymeasurementstopenetrometerreadingsthroughregressionanalysishaveoftenfailedorresultedinanextremelylowcorrelationcoefficient(Landsbergandothers2003;Froese2004).Allbrook(1986)wasreasonablysuccessfulindevelopingastatisticalrelationshipbetweenbulkdensityandsoilstrength(R2=0.67)whenthesoilstrengthwasmeasuredatornearfieldcapacitymoisturecontent.ThestudywasconductedonvolcanicsoilsincentralOregonandcomparedbulkdensitiesandsoilstrengthinskidrutsandinadjacentundisturbedareas.Soilshadinitialsoilbulkdensitiesaveraging0.80Mg/m3.Atthe5cmdepthhefounda23.2%increaseinbulkdensitiesmea-suredwithanucleardensimeteranda143%increaseinsoilstrengthasmeasuredwithapenetrometer.Itappearsthatthesoilstrengthmeasurementsweremoresensitiveandresponsivetochangesinsoilconditions,butitisalsoclearthatastandardofdetrimentalsoildisturbancethatdictateslessthana15%changeinbulkdensitywillnotbetheappropriatepercentagestandardwhencomparingsoilstrength(penetrometer)readings.TheUSDAForestServiceusesathresholdvalueofa15%increaseinbulkdensityfordeterminingwhensoilcompactionhasreachedalevelthatisdetrimentaltobiomassproduction(Powersandothers1998).

Characterization of Ash-Cap Soils _________________________________Soilscharacterizedasash-capsoilsareoftenderivedfromavarietyofvolcanic

eruptions,themostcommonbeingtheeruptionofMountMazamaatCraterLake,Oregon.Thesesoilsareoftenconsideredsurficialdeposits,overlayingthesoilderivedfromthebaserockbydepthsthatvaryfrom15cmtoseveralmeters.Theyarefrequentlycharacterizedinthesiltloamorsandyloamtexturalcategoriesofsoils.Mostash-capsoilsarecharacterizedbylowbulkdensities,generallylessthan0.75g/cm3,andbyhighporosityandlowshearstrength(Page-Dumroese1993;CullenandMontagne1981;Davis1992).Thepredominanceofsilica(glassfragments)inthesoilcontributestothewaterholdingcapacityofthesoil.Thedistributionofmicro-andmacro-porespacesprovidesmanyareasforholding



water,especiallyinthemicro-porespaces.Oneeffectofcompactionmaybetodecreasethemacro-porespacethatiseasilyassessabletoplants,butnotthemicro-porespace.Ash-capsoilscanalsobecharacterizedbyrelativelylowclaycontent.Thisgenerallymeansthattherewillbeverylittlecohesionandinternalbondinginthesoil.Withoutclay,therewillbeverylittleshrinkingandswellingandthismayaffecttherateofsoilrecoveryfromcompaction.

Althoughash-capinfluencedsoilsarenon-cohesive,theydonotseemtorecovereasilyfromcompaction.Froehlichandothers (1985)observedcompactiononandoffskidtrailsonseveralharvestedsitesincentralIdaho.Forsoilsofvolcanicorigin,therewasareductioninthepercentdifferenceindensityonandofftrailswithtime,buttheyalsofoundthatsoilbulkdensityonvolcanicsoilswerestill26%higherat15cmdepthinthetrailsthanofftrails20-25yearsafterharvest-ing.Oneriskwithsoilrecoverystudiesthatconsiderbulkdensitiesindisturbedandundisturbedareas is that theymaynotbecomparing thesamesoil typesandtexture.Forexample,ifthedisturbancealsodisplacedsoilonaskidtrail,thecomparisonmaybebetweenthesurfacehorizonoftheundisturbedsoilandasub-horizonofthesoilontheskidtrail.

Thereareseveralhypothesesonwhyash-capsoilsdonotrecovermorequickly.Oneisthatthecompactionactivitybreaksdownthesoilparticlesand/orrealignsthemintomoreofaplatystructurethatallowsthemtofitclosertogetheraftertraffic.Anotheristhatthejaggededgesofthesilicadominatedash-capsoilpar-ticlesarephysicallylockedduringcompaction.Sinceclaycontentislow,thereislittlenaturalshrinkageandswellinginthesoil.Otherfactorsmayberelatedtothehighinitialpercentchangeinbulkdensitythatgenerallyoccursandthelackofasignificantfreeze-thawcyclesinthedrierregionsoftheintermountainwesternUSA.

Cullen and others (1991) characterized two ash-cap soils in their work inwesternMontana.UsingastandardProctortesttheydeterminedtheoptimummoisturecontentforcompactionofashcapsoilstobeabout228g/kg(22.8%)and256g/kg(25.6%)inthesurfacelayerwithaprojectedmaximumbulkdensityatthismoisturecontentof1.50Mg/m3and1.36Mg/m3forashoverquartziteorlimestonetill,respectively.Thesebulkdensitiesaremuchhigherthanthoseen-counteredinevenheavilycompactedforestsoilsasaresultofforestoperations.GiventheresultsoftheworkofFroehlichandothers(1980),onewouldexpecttheoptimumwatercontentforcompactionfromforestoperationstobehigherthanthevalueobservedintheMontanatestsandtheresultingmaximumcompac-tiontobelower.FieldobservationsintheMontanasoilsshowedtheirseverelycompactedsitestohaveaveragebulkdensitiesatthe5cmdepthof1.01Mg/m3and0.97Mg/m3forashoverquartziteorlimestonetill,respectively.

Although the relatively lowbulkdensitiesofashcap soilsmake themverysusceptibletocompaction, theresultingbulkdensitiesofcompactedsoilssel-domexceed1.0Mg/m3.Theimpactofthisdegreeofchangeinbulkdensityonfutureforestproductivityisnotthesubjectofthispaperbutthegeneralimpactofcompactionontreegrowthhasbeenstudiedinanumberofdifferentsettingsovertheyears(Froehlich1979;Davis1992;Powersandothers2004).Whilein-creasedbulkdensityassociatedwithmachinetraffichasgenerallybeenshowntoreducetreegrowth,theextentofthegrowthreductioninash-capsoilsisnotwelldocumented.Growthreductioncanpossiblybeattributedtoareductioninthewaterholdingcapacityofthesoil,butthechangeinpore-sizedistribution



withintheash-capsoilsaftercompactionmayalsoaffecttreegrowth(Powersandothers2004).Theuseof15%percentchange that isusedasa thresholdvaluefordeterminingdetrimentalsoilcompactionbytheUSDAForestServicemaybeineffectiveforallsoilssinceeachsoiltexturalclassvariesininitialbulkdensityvalueandbiologicalsignificanceofthatchange(WilliamsonandNeilsen2000).Blockandothers(2002)suggestthatcombiningsoilbulkdensityorsoilstrengthmeasurementswithasurfacedisturbanceregimecanbeausefulmethodformonitoringharvestingimpactsonsoil.

Case Studies of Operations on Ash-Cap Soils _______________________Compactiononsomeash-capsoilshasbeenfoundtopersistforlongperiods

oftime,particularlyatdepthsof15cmandgreater.Geistandothers(1989)foundsignificantcompactiononstudysitessampled14to23yearsafterharvestintheBlueMountainsofOregon.Althoughaveragebulkdensitiesdidnotvarygreatlybetweenharvestedandundisturbedareaformostsites,0.67Mg/m3onundisturbedversus0.71Mg/m3onharvested,therewasamuchwiderrangeofbulkdensitiesinthedisturbedareasindicatingareasofsignificantcompactionandareasoflikelydisplacement.Inthemostdisturbedunit,averagebulkdensitywas0.66Mg/m3ontheundisturbedareaand0.80Mg/m3ontheharvestedarea,buttherangeofobservedbulkdensitiesonthedisturbedsiteswasevenwider.

Davis(1992)observeddifferenceinbulkdensitiesondisturbedandundisturbedareas inanash-cap soilwith sandy loam texture.He found theaveragebulkdensityofdisturbedvolcanicashsoilstobe35%higherthantheundisturbed,0.73g/cm3versus0.98g/cm3.HeconductedstandardandlightProctortestsonthesoilanddeterminedamaximumbulkdensitywiththestandardProctortestof1.07g/cm3atamoisturecontentofabout35%.HealsofoundarelativelyflatcurveacrossarangeofmoisturecontentsforlighterProctortests.

AnotherstudyconductedintheBlueMountainsofOregon(SniderandMiller1985)illustratestheimpactofsoilmoisturecontentonoperationalresults.Theyestablishedastatisticalsplit-plotdesigntolookatsoilcharacteristicsonskidtrails,onbermsoftrails,inobviousfireringswhereslashhadbeenpiledandburned,inareaswithsomegeneraldisturbance,andinundisturbedareasfiveyearsafterthelastharvest/sitepreparationactivity.Bulkdensitiesinthecontrolareaaver-aged0.68Mg/m3atthe3.2cmdepth,0.89Mg/m3atthe10.8cmdepthand0.92Mg/m3atthe18.4cmdepth.Generallytherewerenosignificantdifferencesinbulkdensitiesatanydepthamong the fourvariationsand thecontrol.Theauthorssuggestthatthereducedlevelofcompactionmayhavebeenafunctionofdrysoilconditionsduringtheperiodofoperations.

AnexperimentontheColvilleNationalForestinnortheasternWashingtonin-volvedanalysisofharvestingeconomicsandsoilimpactsforanumbervariationsinharvestingsystemsandtrailspacingforharvestingequipmentonbothsteepandgentleslopes.Thesteepslopeunitsinvolveduseofacableyardingsystemcoupledwithmechanizedharvestingequipment.Oneunitalloweddownhillforwardingwithaground-basedcut-to-lengthforwarder.Gentleslopeunitsweredesignedwithvaria-tionsinthedesignatedtrailspacingwithsomeallowanceforthefellingmachinetotravelofftrailinsomeunits(Johnson1999;Keatley2000;Johnson2002).

Soilanalysisinvolvedbulkdensityandpenetrometermeasurementsbeforeandafterharvestoperations(Landsbergandothers2003).Studyconclusionssuggest



thatcompactionresultingfromanearlier fire-salvageharvestingoperationhasremained for at least 70years.Conclusionsnote that compactionwasnot asgreatonsteepterrainwherethecablebasedsystemswereused,butalsonotethatthesoilsweresandierinthatareaandwerelikelytobemoreresistanttochangesinsoilstrength.Changesinsoilstrength,asmeasuredwitharecordingpenetrometer,showedanaverageof127%increaseinresistancetopenetrationinthesurfacelayer(0to10cm)andan89%increaseinresistancetopenetrationatdepthsof15to25cmonskidtrailsinthegroundbasedunits.Thiscontraststochangesof–3%forthesurfacelayerand43%atdepthsof15to25cminthesteeperunits.Differencesonandoffskidtrailsatthe0to10cmdepthaveraged63%inthegroundbasedunitsand10%inthesteepslopes.Differencesatthe15-25cmdepthaveraged26%forbothunits.Thereweresignificantdifferencesbetweenthetypesofharvestingsystem,however.Forexample,thedifferencesbetweenonandoff trail resistancetopenetrationfor thecut-to-lengthsystemwas15%atthe0-10cmdepthand3%atthe15-25cmdepth.Soilconditionsafterharvestingthatremainedwithinlimitsofthespecifiedguidelines,butresultsalsoreflecteddifficultiesassociatedwithinterpretationofpenetrometerresultswhenreadingsaretakenoverafullfieldseasonthatincludessignificantchangesinsoilmoisturecontent(Landsbergandothers2003).

Inonestudy,ash-capsoilsinnorthernIdahowereshowntoreachtheirmaxi-mumbulkdensityafter4tripswitharubber-tiredskidder.Subsequenttripsdidnot result in further increases inbulkdensity.However,pore-sizedistributioncontinuedtochangeafter4ormoretrips(Lenhard1986).Althoughbulkdensitydoesnotappear tochangeafterseveralpasses,otherphysicalpropertiesmaycontinuetochangetothedetrimentofsoilproductivity.Ifsoilpore-sizedistribu-tioncontinuestochange,thenplant-waterrelationshipsarelikelytobealteredorsoilpuddlingwilloccurforlongerperiodsoftime.

TheresultsreportedondrysoilsinnorthernIdahobyFroese(2004)weresimilartothosereportedinnortheasternOregon(SniderandMiller1985).Froese’thesisworkinvolvedstudyofacut-to-lengthsystemoperatingonashcapsoils.Bulkdensitiesinthecontrolaveraged0.95Mg/m3atthe10cmdepth,1.10Mg/m3atthe20cmdepthand1.21Mg/m3atthe30cmdepth.Thesevaluesarehigherthantypicalbulkdensitiesforash-capsoilswithminimaldisturbanceandmayhavecontributedtothelackofchangeafteroperations.TheyarealsotypicalofbulkdensitiesmeasuredonskidtrailsaftermachineoperationsasillustratedinthecasestudyforWesternMontana(Cullenandothers1991).Therewasvirtuallynochangeinbulkdensityafterthepassageoftheharvesterandonepassoftheforwarder.Someincreaseinbulkdensitywasdetectedatthesurfacelayerwithincreasednumbersofforwarderpasses.Operationswerealsoconductedinlatesummerwhensoilswerequitedry.

Cullenandothers(1991)reportedchangesinbulkdensityasaresultoftrafficat three soildepthson soils inWesternMontana.Bulkdensity in the surfacelayerofashoveralimestonetillat5cmchangedfrom0.61Mg/m3withnotraf-ficto0.84Mg/m3withmoderatetrafficandto0.97Mg/m3withseveretraffic.Thechangesat15cmwerealsosignificant,changingfrom0.53Mg/m3intheundisturbedcaseto0.97Mg/m3and0.93Mg/m3formoderateandseveretrafficrespectively. In their conclusions they note that the volcanic surface horizonoverlyingtheglacialtillsoilswaswell-graded,cohesionless,andwaspronetovibratorycompaction.



Controlling Compaction __________________________________________Methodsoflimitingcompactionimpactsonsoilsgenerallyinvolvecontrolof

thetrafficpatternsofequipment,restrictionofvehiclestodesignatedtrailsandareas,andcontrolovertheseasonsofoperation.Sincetopographyplaysamajorroleintheredistributionofwateronasite,depressionsinthelandscapemayhavehighermoisturecontentandbemorepronetocompactiondamagethanareashigheronthelandscape.Designatedtrailscanavoidthesesiteswhenneeded.

Theuseoflowgroundpressuremachinesandcoveringoftrailswithslashmatssuchasthosegeneratedwithcut-to-lengthsystemscanlimittheconsequencesofoneortwopassesofequipment,butdonotappeartobeeffectiveinminimizingsoilcompactionwhenequipmentmustusetrailsmultipletimes(Froese2004;Han2005).Inseveralstudiesofmechanizedequipment,onepassoftheharvestingmachinedidnotappeartosignificantlychangebulkdensityinthesoils(Froese2004;Han2005).Subsequentpassesoftheskiddingorforwardingequipmentdidincreasesoilbulkdensities,butcompactionwaslimitedtothepercentoftheareainmajortrailsorjustintherutsofwelldefinedforwardertrails.

Increasingspacingbetweenoperationaltrailscandecreasetheoverallimpactonanarea,butcanalsohavenegativeeconomicconsequencesbecauseoftheincreasedcostofmovingcutlogsandtreesincreaseddistancestotheoperationaltrails(Johnson2002).Carefuloperationalplanningcanmitigatesomeofthehighercostsassociatedwithincreasedtrailspacing,however.Itmayalsobepossibletoallowthefellingequipmenttooperateinalimitedfashionoffestablishedtrailsandtobunchharvestedmaterialtothetrailforprocessingand/orforwarding.

Limitingoperationsduringperiodsofhighsoilmoisturecontentwillalsolimitsoilimpacts.Thisgenerallywilltranslateintoseasonalrestrictionsonequipment,withmostoperationstakingplaceinlatesummerandearlyfall.Drysoils(<15%soilmoisturecontent)caneffectivelysupporthighergroundpressuresandresultinmorelimitedsoilcompactiontothesurfacemineralsoil(>10cm)(Han2005).Winter operations may be possible with minimal soil impact if the ground isfrozentodepthsof10to15cm(Flatten2002)orhassufficientsnowcover(atleast15cm).

Another option for minimizing soil compaction, but which can also havesignificanteconomicconsequencesistoshiftfromground-basedharvestingtocableorhelicopterharvestingsystems.Bothoftheseoptionscanbestructuredtohaveminimalsoilimpacts,butwillgenerallyincurhighercoststhanground-basedsystems.

Summary and Suggested Areas of Future Research ________________Ash-capsoilsarederivedfromavarietyofvolcaniceruptionsandaremostoften

classifiedinthesiltorsandyloamcategories.Theyarealsocharacterizedwithlowbulkdensity,highporosity,andhighwaterholdingcapacity.Theytendtobenon-cohesiveandbecauseoftheirrelativelylowstrength,arehighlysusceptibletobothvibratoryandcompressivecompaction.Compactionisgenerallyviewedinanegativecontextwithrespecttolong-termsiteproductivityandsustainableforestmanagement.Theresultsofseveralstudiesintheintermountainwestillus-tratethatbothbulkdensityandsoilstrengthvaluesweresignificantlyincreasedduringground-basedharvestoperations,butthattheresultingbulkdensitiesofcompactedash-capsoilsareoftenbelowtheinitialbulkdensitiesofothersoil



textures.Thelong-termeffectsofthechangesinfactorsonsiteproductivitystillneedtobestudiedthroughcontrolledexperiments.

Sinceash-capsoilshaverelativelylowbulkdensitiesbeforeoperations,theymayexperienceaveryhighpercentchangeinsoilstrengthandbulkdensity.Insettingstandards,it isnotclearwhetherthefocusshouldbeonthefinalbulkdensityorsoilstrengthreading,theabsoluteamountofchange,orthepercentchange.Ifsoilstrength,asmeasuredbythepenetrometer,isrecommendedasastandardmethodforsoilmeasurement,correspondingthresholdlevelsofpercentandabsolutechangewillneedtobeestablished.

Theprocessofsoilcompactioncanbeexplainedbyengineeringpropertiesofsoils,butthedegreeofsoilcompactioncreatedinfieldsettingsishighlyin-fluencedbyavarietyoffactorsincludingdistributionofparticlesizes,presenceoforganicmatter,soilmoisturecontent,andsoiltexture.Bulkdensityandsoilstrengtharecommonlyusedtomeasurethedegreeofsoilcompaction,butthestatisticalcorrelationsbetweentwovariablescanbeverylowwhensoilstrengthisnotmeasurednearfieldcapacityofthesoil.Therelationshipsbetweenbulkdensityandsoilstrengthandtheothercriticalsoilfactorssuchaswaterholdingcapacityislessclear,however.Additionalworkisalsoneededtodeterminetheeffectofthedepthoftheash-caponsoilresponsetomachinetraffic.

Although ash-cap soils are susceptible to both vibratory and compressionforces,thespecificvibratoryandcompressiveforcepotentialoftheequipmentoperatinginvariousharvestingandsitepreparationfunctions(cutting,transport-ing)isnotknown.Researchonthevibratoryeffectsofequipmentandwhetherchangesinmachinedesigncouldreducethiseffectwouldbeveryusefultoforestmanagementstrategies.

Several studiesalso found thatchanges inbulkdensityandsoil strength inash-caparelongterm(>70years)andthatrecoverytimeforash-capsoilsisex-pectedtobeslow.Thesestudiesnotedthatsoilcompactionwasgenerallylimitedtoskidtrailsandtopsoillayers(<30cm).Harvestingequipmentused,seasonofoperationandharvestplanningweremajorfactorsinaffectingsoilcompaction.Controllingcompactionofteninvolvesuseoflowimpactequipmentselection,useofdesignatedskidtrails,andlimitationofoperationstodryseasonsorwhenthegroundisfrozen.Theuseoflowgroundpressuremachinesandcoveringtrailswithslashinacut-to-lengthloggingmayhelpreduceimpactsonsoils,especiallysoildisplacement.

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P. R. Robichaud, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Moscow, ID. F. B. Pierson, U.S. Department of Agriculture, Agricultural Research Service, Northwest Watershed Research Center, Boise, ID, . R. E. Brown, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Moscow, ID.

Abstract Afterprescribedburnsatthreelocationsandonewildfire,rainfallsimulationsstudieswerecompletedtocomparepostfirerunoffratesandsedimentyieldsonash-capsoilinconiferforestregionsofnorthernIdahoandwesternMontana.Themeasuredfireeffectsweredifferentiatedbyburnseverity(unburned,low,moderate,andhigh). Resultsindicatethatthisdry,undisturbedash-capsoilexhibitshighrunoffratesandisnaturallywaterrepellentat thesurface.However, theunburned,undisturbedash-capsoil isnothighlyerodibleduetheprotectivedufflayeronthesurface.Whenash-capsoilwasexposedtoprolongedsoilheating(highseverityburn),surfacewaterrepellencywasdestroyedandastrongwaterrepellent layeroccurredafewcentimetersbeneaththesoilsurface.Withthesimulatedrainfall,thenon-waterrepellentsurfacelayerbecamesaturated;thusmakingthesoilabovethewaterrepellentlayerhighlyerodible—especiallyduringhighintensityrainfall.

Keywords: waterrepellentsoils,rainfallsimulation,burnseverity,runoff,erosion.

Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils

P. R. Robichaud, F. B. Pierson, and R. E. Brown

Introduction

Fireisanaturalandanimportantpartofdisturbanceregimeforforestecosystemsandmanylandscapesarewell-adaptedtothisnatural firecycle.Wildfiresuppressionhasdominatedforestmanagement for thepastcenturyandhas interferedwith thesenatural fire regimescausingunnaturalaccumulationsofforestfuels.Althoughmanagedforestsburnlessfrequentlythantheunmanagedforests,thewildfiresthatdooccurarelargerandmoreseverethaninthepast,causingmoresevereandlong-lastingeffects.Fireeffectsonforestsoilmayincludefire-inducedsoilwater repellency, reduced infiltration rates, increasedoverland flow,andincreasedpeakflow,whichoftenresultinincreasedwaterandsedimentyields.


Robichaud, Pierson, and Brown Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils

Burn Severity

Burnseverity,aqualitativemeasureoftheeffectsoffireonsiteresources,isausefulconceptforcomparingfires(HartfordandFrandsen1992;RyanandNoste1983).Arangeoffireandpostfireconditions,suchasfireintensity,fireduration,crownconsumption,soilcolor,andproportionoflitterremaining,aretypicallyusedtoclassifyburnedareasintodiscreteclassesofhigh,moderate,orlowburnseverity.Although someaspectsofburn severitycanbequantified,no singlenumbercanbedeterminedtomeasure‘resourceimpact’.

Thecomponentofburnseveritythatresultsinthemostdamagetosoilsisfireduration,becausedurationgenerallydeterminesthetemperatureanddepthofsoilheating.RyanandNoste(1983)createdaburnseverityclassificationsystem(expandedbyJain(2004))thatestimatestheamountofsoilheatingthatlikelyoc-curredduringthefirebasedonpostfirelitteramountsandmineralsoilcoloration.Becauseitisspecifictosoil,theRyanandNoste(1983)definitionofburnseveritywasusedtoevaluateburnseverityatresearchsitesdiscussedinthispaper.

Water Repellency

Naturallyoccurringwater repellent soilsoccur ineverycontinentandhavedifferentinfiltrationpropertiesthanwettablesoils(Letey2005).Firecreatesorenhanceswaterrepellencyinsoils(Doerrandothers2000).Assurfacevegetationisburnedandthesoilisheated,organicmatterinandonthesoilisvolatilized,andasignificantfractionofthesevaporizedorganiccompoundsmovefromthesurfaceintothesoilprofile(DeBanoandothers1976).Thesealiphatichydrocar-bonvaporscondenseonsoilparticlesinthecoolerlayersbeneaththesurfacetoformawaterrepellentlayer.Thiswaterrepellentlayerisgenerallywithinthetop5cmofthesoilprofile,non-continuous,androughlyparalleltothesurface(Clothierandothers2000;DeBano2000).Ingeneral,coarsesoils(lowclaycon-tent)aremoresusceptibletobecomingwaterrepellentthanfinersoils(highclaycontent)duetothelowerspecificsurfaceareaofcoarsesoilparticles.However,whenwaterrepellencyisestablishedinfine-grainedsoils,itcanbeequallyormoreseverethaninacoarse-texturedsoil(Doerrandothers2000;RobichaudandHungerford2000).

Fire-inducedsoilwaterrepellencyhashightemporalandspatialvariability(Letey2005).Thedegreeanddepthofpostfirewaterrepellencyisrelatedtosoilheatingduringthefire,which,becauseofitsdependenceonantecedentsoilmoisture,forestfloorthickness,burnduration,postfiresmoldering,etc.,ishighlyvariable.Fire-inducedsoilwaterrepellencyhasbeenfoundtovarybothinthehorizontalandtheverticaldirectionsatthe1cmscale(Hallettandothers2004;Gerkeandothers2001).Fire-inducedwaterrepellencyismostoftendetectedat1to3cmbelowthesurface(Huffmannandothers2001).Inaddition,soilwaterrepellencyistransientandisrelatedtosoilmoisture.Generally,bothnaturalandfire-inducedsoilwaterrepellencyislostduringlongwetperiodsandisre-establishedupondrying, causing short-term or seasonal variations (Robichaud and Hungerford2000).Fire-inducedsoilwaterrepellencyistemporarybecausethehydrophobicsubstancesresponsibleforwaterrepellencyareslightlywater-solubleandslowlydissolvesuchthatwaterrepellentsoilconditionsarebrokenuporwashedawaywithinseveralyearsafterthefire.


Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils Robichaud, Pierson, and Brown

Infiltration

Inwaterrepellentsoils,watermaymovethroughawettablesurfacelayer,anduponreachingawaterrepellentlayer,flowlaterallybelowthesurface(DeBano1981).Giventhespatialvariabilityofwaterrepellency,watermayflowprefer-entially,viacolumns,or‘fingers,’throughthelesswaterrepellentareasforminganunevenwettingfront(RitsemaandDekker1994,1995).Infiltrationonwaterrepellentsoilsisalsodependentonthetypeanddistributionofplantsoverthesurface(Shakesbyandothers2000).Someplants,suchaschaparral,decreaseinfiltrationbyaddinghydrophobiccompoundstothesoildirectlyunderthecanopy(DeBano1981).Conversely,infiltrationcanbeenhancedbyrootchannelsandmacropores(remainingafterrootsdecayorburn)thatcanactaspathwaysforinfiltratingwaterthroughwaterrepellentlayers(Meeuwig1971;Sevinkandothers1989;Burchandothers1989;Shakesbyandothers2000).

Overland Flow and Erosion

Overlandflowandsoilerosionratesaredependentonarangeofinter-relatedfactorsthatincluderainfall(e.g.,amount,intensity,duration),soil(e.g.,erodibility,particlesize,poresize,bulkdensity,waterrepellency),topography(e.g.,slope,aspect),andbiotic(e.g.,vegetation,groundcover,animaluse,naturalandhumandisturbances).Becauseof the reduction in infiltrationcapacity inwater repel-lentsoils,postfireincreasesinoverlandflowanderosionareoftenattributedtofire-inducedwaterrepellency(Doerrandothers2000).However,itisdifficulttodeterminetheproportionofpostfireincreasederosionthatcanbeattributedtosoilwaterrepellency.Firecanalsoincreasetheerodibilityofsoilthroughreduc-tionofprotectivegroundcoverandsoilorganicmatter,sealingofsoilpores,lossofwaterstoragecapacityinthelitterandduff,lossofsoilmoisture,breakdownsoilaggregates,andreductionof soilparticlesize (DeBanoandothers1998).Thus,thecontributionofsoilwaterrepellencyontotalpostfireerosionisoftendifficulttoseparatefromotherfireimpacts.

Cautionmustbeusedwhenextrapolatingmeasurementsofoverlandflowfromsmallplotstodeterminethepotentialrunoffonthehillslope-orcatchment-scalewheredifferentialflowpatternsmayhavesignificantlymoreeffect(Shakesbyandothers2000;Imesonandothers1992).AfteraEucalyptusforestfireinAustralia,ProsserandWilliams(1998)foundthatsmallplotsproducedgreaterrunoffandsedimenttransferthanwasobservedatthehillslopecatchmentoutlet.Thelackofspatialcontiguityinsoilwaterrepellencyandtheexistenceofdifferentialinfiltra-tionflowpatternsmaycreatescattered‘sink’areasacrossahillsidewherewaterinfiltratesand,asaresult,doesnotreachthebaseofacatchmentasoverlandflow(Imesonandothers1992;ProsserandWilliams1998).

Study Objectives

Smallplotrainsimulationdatafromthreeprescribedburns(northernIdaho)andonewildfire(westernMontana)areusedtocomparefireeffectsonrunoffanderosionofash-capsoils.Thetwostudies(prescribedfirestudyandthewild-firestudy)hadcommonsitecharacteristics(coniferforestedenvironmentsandash-cap soil types) and test procedures (rainfall simulation), which facilitated



thecomparisonoffirstyearpostfiredatafromthefourfiresto:1)examinefire-inducedandnaturalash-capsoilwaterrepellency;2)comparerunoffrates;and3)comparesedimentconcentrationsandsedimentyields.

Methods _______________________________________________________

Prescribed Fire

Site Description—The prescribed fire study was conducted in the FernanRangerDistrict,IdahoPanhandleNationalForestintheCoeurd’AleneMountains(48°15’N,116°15’W).Studyplotswerelocatedbetween950to1500meleva-tionon14to46percentslopes.ThepredominantsoiltypeisTypicVitrandepts,asiltloamderivedfromvolcanicash-influencedloess28to45cmthick,overanEutircGlossoboralfs,amixedloamy-skeletalformedfromPrecambrianBeltrock.Averageannualprecipitationis34incheswithaboutonethirdofthatfallingassnowinthewintermonths(Abramovichandothers1998).Vegetationoftheareaistypicalofthewesternhemlock/queencupbeadlily(Tsuga heterophylla/Clintonia uniflora)habitattype(Cooperandothers1991).

IgnitionofthefirstharvestedunitwasinthespringonApril25(BumbleBee).IgnitionofthesecondburnoccurredinthefalltwoyearslateronSeptember30(Buckskin I). The third harvest unit was ignited in the summer on August 25(Buckskin II). For eachof the threeprescribedburns, ahelitorch-ignited stripheadfirewasstartedatthetopoftheslopewithfirestripsplacedaboutevery30-40mdowntheslope.Ignitionwasgenerallyveryrapid,andtheentireunitignitedwithin30min.

Plots—Beforeeachprescribedfire,sixpaired1-m2plotsweresystematicallyselectedinthestudyareastorepresenttheaveragefuelconditionandaverageslope,withoneplotdesignatedforrainfallsimulationandtheotherforsoiltemperaturemeasurements.Foursteelpinswereinstalledflushwiththeforestfloorsurfaceineachplottoestimateforestfloorconsumption.Inthetemperature-measurementplots, these forest floor pins were located near thermocouples. Temperaturesduringthefirewererecordedwitheightchromel-alumelthermocoupleslocatedatthelittersurface,inthehumus,atthehumus-mineralsoilinterface,andinthemineralsoilat1,2,4,8,and10cmbelowtheinterface.Temperaturesduringtheburnwerefirstrecordedwhenthesurfacetemperaturereached80°Candcontinuedeveryminutethereafterfor36h.Immediatelybeforeburning,samplesof thewoody fuels, forest floor,andmineral soilwerecollected todeterminemoisturecontent.

Oneachoftherainfallsimulationplots,afour-sidedsheetmetalframewasinstalled.Threeframesideswere15cmtallandinstalledwith5cminsertedintothemineralsoil,andthefourth,downslopesideoftheframewas5cmtallandinsertedfullyintothesoil(noextensionabovethesurfaceofthesoil)allowingrunoffandsedimenttoleavetheplot.

Rain Simulation—Withindaysof theprescribed fire,a30-min rainsimula-tionwasconductedattheexistingsoilmoistureconditionasdeterminedfromacompositesoilsamplewastakenneartheedgeoftheplotframe.ThesimulatedrainfallwasappliedtoeachplotusingaUSDA-ForestServicemodifiedPurdue-typeoscillatingnozzlerainfallsimulatorwithspecificationsasdescribedbyMeyer



andHarmon(1979).Therainfallsimulatorproducedanaveragerainfallintensityof38mmh–1fortheBumbleBee(spring92)burnsite.AftertheBumbleBeesimula-tions,thesimulatedrainfallintensitywasincreasedtoensurethattherainfallrateexceededtheinfiltrationcapacityofthesoil.Rainfallintensitywas100mmh–1fortheBuckskinI(autumn94)andBuckskinII(summer95)burnsites.Sevenraingaugeslocatedaroundthe1m2plotsverifiedtherainfallamount.

Acoveredtroughatthelowerendofeachplotconductedrunoff(waterandsediment)throughapipefittedwithavalvethatallowedfortimedvolumesampling.Thesamplesweremanuallycollectedin1000mlbottlesat1-minintervals.Attheendofthesimulationrun,anysedimentremaininginthetroughwaswashedintoasamplebottle.Allrunoffsampleswereweighedandoven-driedtodeterminerunoffratesandsedimentconcentrations.

Wildfire Study

Site Description—The wildfire study was conducted in the Bitterroot Na-tionalForest(46°4’N,114°0’W)ofwesternMontanawhere,inthesummerof2000,lightningstrikesignitedtheBitterrootComplexFires.Thesefiresburned101,000ha—40percentathighburnseverityasdeterminedbypostfireappear-ance(USDA2000).ThepredominantsoilisderivedfromvolcanicashoverhighlyweatheredgraniteandisclassifiedasasandyskeletalAndic-Dystrocryept.Themeanelevation isapproximately1,950meterswithslopes ranging from25 to55percentanddominantlywest-southwesternaspects.Vegetationoftheareaistypicalofthesubalpinefir/menziesii(Abies lasiocarpa/Menziesia ferrugineah.t.)foresthabitattype.

Plots—Withinanareaofhighburn severity, four study siteswere selectedbasedoncomparableslope,aspect,andgroundcovercharacteristics.Oneachofthefoursites,15plotsof0.5m2wererandomlylocatedanddelineatedbyafour-sidedsheetmetalframeaspreviouslydescribed.Approximately3kmnorthoftheburnedstudyarea,threeunburnedsiteswereselectedsuchthattheslope,aspect,andsoiltypewerecomparabletotheburnedareasitesand,inaddition,thevegetativecharacteristicswerecomparableamongtheunburnedstudysites.Ineachofthethreeunburnedsites,7plotsof0.5m2wererandomlylocatedanddefinedbytheinstallationofsheetmetalplotframesasdescribedabove.

Directlyadjacenttoeachplotframe,waterrepellencywasmeasuredusingthewaterdroppenetrationtime(WDPT)adaptedfromDeBano(1981).Eightwaterdropswereplacedonanexposedsurfaceof themineral soiland the time toinfiltrateintothesoilisobserved.Thedegreeofwaterrepellencyisdeterminedbythelengthoftimethewaterdropsitsonthesoilwithoutbeingabsorbed:0to5sec=none;6to60sec=slight;61to180sec=moderate;181to300ormore=severe.Themaximumobservationtimewaslimitedto5minutes.Ifthewaterdropsinfiltratedinlessthan5seconds,thetestwasrepeatedat1cmdepthbelowthesurface.Thisprocesswasrepeatedat1cmincrementstoamaximumdepthof5cm.

Neartheedgeoftheplotframe,acompositesoilsamplewastakentoassesssoilmoisture.Groundcoverwithineachplotwasdetermined.

Rainfall Simulation—Withindays after the firewas contained, a simulatedrainfalleventwithameanrainfallintensityof100mmh–1wasappliedtoeachofthe102plotsfor60minusingtheUSDA-ForestServiceandtheUSDA-Agricultural



ResearchServiceoscillating-armrainfallsimulatorswithspecificationsasdescribedbyMeyerandHarmon(1979).Datafromthefirst30minutesofeachsimulationwereusedforcomparisonsandanalysis.Duringtherainfallsimulation,samplesofrunoffandsedimentwerecollectedthroughacoveredtroughatthedownslopeedgeofeachplotasdescribedfortheprescribedburnsabove.Thesamplesweremanuallycollectedat1-minintervalsforthefirst14min,thenat2-minintervalsfortheremainderofthe60-minrun.Allrunoffsampleswereweighedandoven-driedtodeterminerunoffvolumeforeachinterval,totalrunoffvolume,sedimentconcentrations.

Analytical Methods

ThedatafromtheBumbleBeeprescribedfiresitewerenotincludedinthestatisticalanalysisbecausetherainfallapplicationrateof38mmh–1wasmuchlessthan100mmh–1rainfallapplicationrateappliedatallothersites.Thetotalrunoffanddrysuspendedsedimentweightwerecalculatedforthefirst29to30minofthefirstsimulationfortheBuckskinIandIIsitesandforthefirst29to31minoftheyear2000simulationsattheBitterrootsites.Runoffandsuspendedsedimentwerenormalizedbyareatoaccountforthedifferentplotsizes.Runoffratiosaretotalrunoff(mm)dividedbytotalrainfallapplied(mm)foreachsimula-tion;therainfallisadjustedfortheplotsize.

Results and Discussion ___________________________________________

Burn Severity

Variedantecedentconditions for the threeprescribedburns resulted indif-ferentialsoilheatingandarangeoffireeffectsonthesoil.BumbleBee,aspringburn,hadthehighestpre-firesoilandduffmoisturecontents(61to69percentand125percent,respectively)andthelowestmineralsoiltemperatures(20to80°C)andproportionofduffconsumed(28percent)duringthefire(table1).BumbleBeewasalowburnseverityfire.BuckskinIwasburnedinthefallwiththedriestconditionsofthethreeprescribedburns(table1)andwasclassifiedmoderateburnseverity.BuckskinII,asummerburn,hadslightlyhigherpre-burnfuelandsoilmoistureconditionsthanBuckskinIandwasalsoclassifiedmoder-ateburnseverity (table1).ThestudyareaswithintheBitterrootComplexFireareawereinunburnedandhighburnseverityareas.Thesefourfiresonash-capsoils provided four burn severity conditions—unburned (Bitterroot), lowburnseverity(BumbleBee),moderateburnseverity(BuckskinIandII),andhighburnseverity(Bitterroot).

Moisture Content and Water Repellency

Soilmoisturesimmediatelypriortotherainfallsimulationswerehigherintheprescribedfiresitesthanthewildfiresites(table2),butprobablynothighenoughtochangethesoilwaterrepellencyresponse(RobichaudandHungerford2000).SoilwaterrepellencywasdirectlyassessedintheBitterrootstudy,wherebothburnedandunburnedsoilshadstrongwaterrepellentresponsesatdifferentdepths.Theunburnedsoilwasseverelywaterrepellentatthesurfacewhiletheburnedsoil



Table 1—Measured conditions before, during, and after three prescribed burns in northern Idaho.

Pre-prescribed BurnFuel and soil moisturecontents and weather conditions Bumble Bee Buckskin I Buckskin II

Fine fuels (0-7� mm) (%) 20 9 10Large fuels (77-�00 mm) (%) 41 11 2�Litter (%) �4 1� 11Humus (%) 12� 4� 4�Soil 0-2 cm (%) �9 40 49Soil 2-� cm (%) �1 29 40Ambient temperature (oC) 22 20 1�Wind speed (kph) �-1� 2-� 0-11Relative humidity (%) 1� �0 �7

Prescribed BurnMaximum soil temperatures (°C) Bumble Bee Buckskin I Buckskin II

Mineral soil surface 20-�0 40-�00 90-2�01 cm below min. soil surface 40-70 40-270 70-1202 cm below min. soil surface 20-�0 40-�0 �0-�0

Post-prescribed BurnOrganic material remaining (%) Bumble Bee Buckskin I Buckskin II

Fine fuels 12 � 0Duff 72 27 ��

Table 2—Pre-rainfall simulation mean ground cover and gravimetric soil moisture content by location.

Gravimetric soilLocations Ground cover water content

- - - - - - - - - - - - (%) - - - - - - - - - - -

Unburned Bitterroot 100 1� Bumble Bee 100 29Buckskin II 9� 2�Buckskin I 70 �0Burned Bitterroot 10 17

hadawaterrepellentlayerat1to2cmbelowthesurface(fig.1).Thecreationofafire-inducedwaterrepellentlayerhasbeenobservedbyotherresearchers(e.g.,McNabbandothers1989;BrockandDeBano1990;ScottandVanWyk1990;Doerrandothers2000).However,thehighburnseverityfireappearedtodestroythenaturalsurfacewaterrepellency,andcreateawaterrepellentlayeratdepth.Doerrandothers(inpress)observedthesameaffectafterwildfiresineucalyptusforestsinAustralia.



Runoff

Thehighest runoff ratio rates (fig.2)andmean runoff amounts (33and32mm)andrunoffratios(0.71and0.67)weremeasuredonthehighandmoderateseverityburnsites—Bitterroot-burnedandBuckskinI,respectively(table3).Theunburned-Bitterroot sites and themoderateburn severityBuckskin II sitehadsimilarrunoffratiorates(fig.2)andmeanrunoffamounts(26and24mm)andrunoffratios(0.54and0.53)(table3).Thisunexpectedlylargerunoffresponseintheunburned-Bitterrootsitesislikelyduetotheshorttimeframeofthesimula-tionandtheresistancetowettingofthedryorganicduffmaterialaswellasthenaturallywaterrepellentdrysurfacesoil.TheBumbleBeeprescribedburnsitehadlowrunoffratiorates(fig.2)andalowmeanrunoffamount(4.7mm)andrunoffratio(0.12)(table3).However,thesedataarenotdirectlycomparabletotheothersitesasthelowerrainfallapplicationratemaynothaveexceededtheinfiltrationcapacityofthesoil.

Sediment Concentrations and Yields

Sedimentconcentrationsandmeansedimentyieldsgenerallyincreasedwithincreasingburnseverity(fig.3andtable3).Sedimentconcentrationsintherainsimulationrunofftendedtopeakinthefirst5min,rapidlydecreaseduringthesecond5min,andslowlydecreaseduringtheremaining20minutesofthesimu-lation(fig.3).Theunburned-BitterrootsitesandtheBumbleBeesite(lowburnseverity)hadthelowestconcentrations,peakingat7and4gL–1,respectivelyanddecreasingtolessthan1gL–1at30min(fig.3).Theseconcentrationsresultedinmeansedimentyieldsof0.027and0.0091kgm–2,respectively(table3).ThelowerrainfallapplicationrateontheBumbleBeesiteprobablyhadlittleaffectonmeansedimentyield(table3)duetothehighgroundcoverremainingafter

Figure 1—OntheUnburned-andBurned-Bitterrootwildfiresites,theportionofwaterrepellentsoil,asmeasuredbytheWaterDropPenetrationTime(WDPT)tests,areindicatedforthesoilsurfaceand1,2,3,4,and5cmdepths.Theshading/hatchingwithineachbarindicatetheseverityofthemeasuredwaterrepellency.



Table 3—Mean runoff, runoff ratio, and suspended sediment yield by location. Standard errors are in parentheses. Dif-ferent letters within a column indicate significant differences at α=0.05. Comparative statistics do not include the Bumble Bee data due to the lower applied rainfall at that site.

Location Disturbance type n Runoff Runoff ratio Sediment yield (mm) (kg m–2)

Unburned-Bitterroot Undisturbed 21 2� (1.�) a 0.�4 (0.0�2) a 0.027 (0.0�9) aBumble Bee Prescribed fire 4 4.7 (1.4) 0.2� (0.04�) 0.0091 (0.002�)Buckskin II Prescribed fire � 24 (2.�) a 0.�� (0.049) a 0.2� (0.90) abBuckskin I Prescribed fire � �2 (1.�) ab 0.�7 (0.19) ab 0.�0 (0.�0) abBurned-Bitterroot Wildfire �0 �� (0.�0) b 0.71 (0.12) b 0.�� (0.�1) b

Figure 2—Therunoffratio(runoff/rainfall)rateforallstudysitesareplotted.TheBumbleBeesitesreceivedaloweramountofrainfallascomparedtoothersites.

Figure 3—Thesedimentconcentrationrateforallstudysitesareplotted.TheBumbleBeesitesreceivedaloweramountofandlessintenserainfallascomparedtoothersites.



thespringburn(table2).TheBuckskinIandII,bothmoderateburns,peakedat47and36gL–1,respectivelyanddecreasedtoabout1gL–1at30min.(fig.3),resultinginmeansedimentyieldsof0.50and0.26kgm–2,respectively(table3).Thehighseverityburned-Bitterrootsitespeakedat38gL–1,andremainedhigherthananyoftheothersitesthroughoutmostofthe30minsimulation,anddecreasedto20gL–1at30min.(fig.3),resultingina0.85kgm–2meansedimentyield,anorderofmagnitudegreaterthantheunburned-Bitterrootsites(table3).Thehighersedimentyieldsforthewildfiresitesreflectthehigherconsumptionoforganicmaterialduringawildfire (longer firedurationandhighersoil tem-peratures)ascomparedtoaprescribedfire.Thisdifferenceinfiresisreflectedinthepostfire,pre-rainfallmeangroundcovers,withtheBurned-Bitterrootsiteshaving10percentgroundcoverandtheBuckskinIandBuckskinIIsiteshaving70percentand98percent,respectively(table2).

Conclusions _____________________________________________________Astrongnaturalsoilwaterrepellencywasdetectedatthesurfaceofthemineral

soilintheunburned,undisturbedash-capsoilwithlowsoilmoisturecontent.The high burn severity wildfire appeared to destroy the surface water repel-lency,andcauseastrongwaterrepellentlayertodevelop1to2cmbelowthesurfaceofthemineralsoil.Soilwaterrepellency,atthesurfaceorslightlybelowthesurface, increasedrunoff;however,below-surfacewaterrepellencyresultsinamuchlargersedimentresponsethansurfacewaterrepellency.Whenthereisfire-induced,below-surfacesoilwaterrepellency,rainfallisreadilyabsorbedbythenon-repellentsurfacesoil(0to1-2cm)whichbecomessaturateddowntothemoreresistantwaterrepellentlayer.Thissaturatedsurfacelayeriseasilydetachedandentrainedwithinthesubsequentoverlandflow.Additionally,finerootsthatbindthesurfacesoiltogetherwerelikelypartiallyconsumedduringthefire,makingsoilparticlesvulnerabletodetachment.

Even in steep forest environments with dry conditions (i.e., severe surfacewaterrepellency),theundisturbed,unburnedsitewithitsintactdufflayerwasnothighlyerodible,despitehighrunoffrates.Duringthe30minofhighintensityrainfall,thedryduffdidnotabsorbmuchwaterandtherainfallflowedthroughthedufflayerandatopthewaterrepellentmineralsoiltotheoutletoftheplots.Consequently,therunoffratesfortheunburned-BitterrootsitesweresimilartothosefoundonthemoderateburnseverityBuckskinIIsite.However,thesedi-mentconcentrationsandsedimentyieldswerelessthantheBuckskinIIduetotheprotective layerofduffmaterial.TheBumbleBee lowseverityprescribedfirealsohadminimalsedimentresponsebecauseofthecharred,butintact,duffremainingafterthefire.Thefireeffectsonsedimentconcentrationsandsedimentyieldsincreasedwithincreasingburnseverity.

Management Implications

Ash-capsoilsareknownashighlyproductiveforestsoils,andprotectingthissoil resource isan important landmanagementconsideration.Prescribed firesshouldbeignitedwhenduffmoisturecontentwillpreventtotalconsumptionoftheprotectivedufflayer.Ash-capsoilsburnedathighseverityarehighlyerodibleandpostfirerehabilitationdecisionsshouldtakeintoaccountthepotentialpostfirehydrologicalandsedimentresponsefrompotentialrainevents.



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Ritsema,C.J.;Dekker,L.W.1994.Howwatermovesinawaterrepellentsandysoil:2.Dynamicsoffingeredflow.WaterResourcesResearch.30(9):2519-2531.



Robichaud,P.R.;Hungerford,R.D.2000.WaterrepellencybylaboratoryburningoffournorthernRockyMountainforestsoils.JournalofHydrology.231-232(1-4):207-219.

Ryan,K.C.;Noste,N.V.1983.Evaluatingprescribedfires.In:Lotan,J.E.;Kilgore,B.M.;Fischer,W.C.;Mutch,R.W.,tech.coords.Proceedingsofthesymposiumandworkshoponwilder-nessfire.Gen.Tech.Rep.INT-182.Ogden,UT:U.S.DepartmentofAgriculture,ForestService,IntermountainResearchStation:230-238.

Scott,D.F.;VanWyk,D.B.1990.Theeffectsofwildfireonsoilwettabilityandhydrologicalbehaviourofanafforestedcatchment.JournalofHydrology.121:239-256.

Sevik,J.;Imeson,A.D.;Verstratun,J.M.,1989.Humusformdevelopmentandhillsloperunoff,andtheeffectsoffireandmanagement,underMediterraneanforestinN.E.Spain.Catena.16:461-475.

Shakesby,R.A.;Doerr,S.H.;Walsh,R.P.D.2000.Theerosionalimpactofsoilhydrophobicity:currentproblemsandfutureresearchdirections.JournalofHydrology.231-232,178-191.

USDAForestService.2000.ValleyphaseI:burnedareaemergencyrehabilitation(BAER)reportFS-2500-8—funding request.Missoula,MT:U.S.DepartmentofAgriculture,ForestService,BitterrootNationalForest.253p.

Management Alternatives for Ash-cap Soils


The Practice of Sustainable Soil Management

Sustainablesoilmanagementcanbedefinedasensuringthebiological,chemicalandphysi-cal integrityof the soil remains for futuregenerations. Sustainability shouldbeaddressedthroughoutallfacetsofforestmanagementincludingimplementationofindividualharvestorstand-tendingplans,developmentofagencyorcompanystandardsandbestmanagementpractices(BMPs),andthird-partycertification.Demonstrationofsustainablesoilmanagement


Mike Curran, Corresponding author, Research Soil Scientist, B.C. Ministry of Forests and Range, Forest Sciences Pro-gram, Kootenay Lake Forestry Centre, Nelson B.C., Canada. (also Adjunct Professor, Agroecology, University of B.C.). Pat Green, Forest Ecologist, Nez Perce National Forest, Grangeville, Idaho. Doug Maynard, Research Scientist, Natural Resources Canada, Canadian Forest Service, Victoria BC, Canada.

Abstract Sustainabilityprotocolsrecognizeforestsoildisturbanceasanimportantissueatnationalandinternationallevels.Atregional levelscontinualmonitoringandtestingofstandards,practices,andeffectsarenecessary forsuccessfulimplementationofsustainablesoilmanagement.Volcanicash-capsoilsareaffectedbysoildisturbanceandchangestosoilpropertiesinfluenceecosystemresponsessuchasproductivityandhydrologicfunction.Soildisturbancefromtimberharvesting,reforestation,orstandtendingismainlyaresultofmovingequipmentandtrees.Compactionandorganicmatterremovalareofprimaryconcern.Theseverityandextentofdisturbancedependontheharvestsystem,soil andclimaticconditions.Ash-cap soilscanbe susceptible todisturbanceand schemes topredictcompaction,displacementanderosionhazardsareusefulforplanningforestmanagementoperations.On-siteeffectsrangefrompermanentlossofgrowingsitesbecauseofroads,tomoresubtlechangesinsoilpropertiesthatultimatelyinfluencesiteproductivity.Off-siteeffectsmay includeerosionand landslides.Soildisturbanceduringoperationsshouldberegulatedandmonitoredtominimizebothon-andoff-siteeffects,whichcantakeyearsordecadestoappear.Foresthealthissuesvaryonvolcanicash-capsoils.AnanalysisofArmillariarootdiseaseincidenceacrosstheNationalFor-estsoftheInlandNorthwestindicatessomepotentialrelationshipsamongrootdisease,andsoilandsitefactors.Thestrongrelationsbetweenpresenceofsusceptiblehostanddevelopmentoffungalbiomassmaybethestrongestcausalagent,withthesoilandsitefactorssupportingthepresenceofthepathogenandsusceptiblehost.Thickerashsoilsofmorenortherlyareasarerelatedtohabitattypesthathistoricallysupportedwhitepineandahigherdiversityoflesssusceptiblespecies.Afterrootdiseasemortalityoccurs,thesemoremesicenvironmentsalsofillinwithotherspeciesrapidly,sohigherlevelsofrootdiseasearemoredifficulttodiscern.Recommendationsaremadeforsoilmanagementandaboutinformationneedsforsoildisturbanceandrootdiseaserelations.

Key words:volcanicash-capsoils,foresthealth,Armillaria,rootdisease,criteriaandindicators,organicmatterdeple-tion,soildisturbance,soilcompaction,sustainabilityprotocols

Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends

Mike Curran, Pat Green and Doug Maynard


ispromoted through reportingprocedures requiredbyapplicable sustainabilityprotocols,andbyhavingthird-partycertificationofforestpracticesandproducts(Curranandothers2005a).

Sustainabilityprotocolsexistatinternationalandnationallevels.Attheinter-nationallevel,theMontrealProcess(MP)includesaWorkingGrouponCriteriaandIndicatorsfortheConservationandSustainableManagementofTemperateand Boreal Forests (Montreal Process Working Group 1997). Some countrieshavedevelopedtheirownprotocolsandproceduresdesignedtotrackandreportprogresstowardmeetingrequirementsofinternationalprotocolssuchastheMP.Forexample,theCanadianCouncilofForestMinistersrecentlydevelopedrevisedcriteriaandindicatorsforsustainableforestmanagement(CCFM2003).

Third-party(eco)certificationofforestpracticesandresultingwoodproductsaroseinresponsetosustainabilityprotocolsandthegreeningoftheglobalmarket-place.OrganizationssuchasSustainableForestryInitiative(AmericanForestandPaperAssociation),CanadianStandardsAssociation,ForestStewardshipCouncil(FSC),andISO1400.1allhavedocumentedreviewprocessesandproceduresforcertification.Protectingstreamsandnaturaldrainagepatterns,maintainingslopestability,and regulating soildisturbancearecommonelementsconsidered. Inaddition,mostrequiresomeadaptivemanagementprocesstoensurecontinuousimprovementofpracticesontheground.Compliancewithcurrentsoildisturbancestandardsisoftenusedasaproxyforensuringsustainability;however,acommonapproachtostandards,andvalidationofthestandardsthroughresearchareim-portantstepsthatmustnotbeoverlookedwhentheseareusedasproxies.Somecertificationschemesalsocallformorerestrictivestandards(e.g.,FSCinBritishColumbiacallsforlowerdisturbancelevelsthanProvincialregulations).

Atthelocallevel,whenmanagingharvest-effectsonsoils,treegrowthandlong-termproductivity,soildisturbancefrommechanicaloperationsisofmostconcern.Soildisturbanceoccurringattimeofoperationscanhavenegative,positive,ornodetectableeffectongrowthorhydrologicfunction.Soildisturbanceatthetimeofoperationsisoftenanindicatorusedinregulatinglong-termproductivityandhydrologiceffects.ThisisbecauseinmanyNAecosystems,weneedatleast10to20yearsdatatodrawconclusionsabouttheeffectsofvariouspracticesongrowthorhydrologicfunction.Indiscussingevidenceforlong-termproductivitychanges,MorrisandMiller(1994)indicatedslow-growingstandsrequire20ormoreyearsofgrowthbeforelong-termproductivityconsequencescanbeascer-tained.Soildisturbanceistheproxythatwecanobserveandregulateatthetimeofharvestingandsitepreparation.However,thisproxyalsoneedstobevalidatedandrevisedovertimeinanadaptivemanagementprocessthatincludesstandards,bestmanagementpractices,monitoring(compliance,effectivenessandvalidation),furtherresearchandstrategicdirectionandrevisionovertime(Curranandothers2005b).Acommonapproachisneededfordescribingsoildisturbancesothatresultsachievedindifferentareasarecomparable(Curranandothers2005c).

Management and Communication Frameworks for Sustainable Soil Management _______________________________________________

Justlikeecosystemclassificationschemes(e.g.,BraumandlandCurran1992)inneighboringBC,organizingsoilintomappableorotherwisedescribableunitsprovidesanimportantframeworkforcommunicatingmanagementexperience,

Curran, Green, and Maynard Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends


researchresults,andconservationefforts.Detailedsoilor landtypemapsareavailableformuchoftheash-capsoilsintheUnitedStates,andreconnaissance-levelsoilmappingisavailableinsouthernBC.Mapsdesignatesoilunits(e.g.,soilseriesindetailedmappingandsoilorlandtypeassociationsinreconnaissancemapping)basedonsoil-formingfactorsofparentmaterial,topography,climateandvegetation,allactingovertime,whichvariesduetogeologiceventslikeglaciationandvolcaniceruptions.Asdiscussedabove,soildisturbancecanalsobeclassifiedandweareworkingtowardsacommonclassificationthereaswell.

Perhapsthemostusefulwayoforganizingsoilunitsforforestmanagementisaconsiderationoftheirriskofdamagefromsoildisturbance.Themostcommondisturbanceofconcerninforestmanagementisfrommachinetrafficduringhar-vesting,sitepreparation,orfuelmanagementtreatments.Thebiggestconcernsassociatedwithmachinetrafficaresoilcompaction,soildisplacement,andsoilerosion.Inaddition,slopestabilityisaconcernonsteeperandwettersites.Toidentifyandmitigatethepotentialforlandslides,terrainmappingand/orterrainstabilityfieldassessmentsareusedonsitesthatexceedcertainslopegradientsorhaveindicatorsofpotentialslopeinstability.

Determiningthesoildisturbancehazardsonagivensiteprovidesaframeworkfordevelopingharvestingstrategiesbyalertingtheprescriptiondevelopertothespecificsoildisturbanceconcernsonthatsite.Forexample,inBC,soildistur-bancedefaultstandardsundertheForestandRangePracticesAct(FRPA)permitup to5or10%netdisturbancewithinacutblockarea (excludingpermanentaccess).IntheInterior,thetriggerfor5%iswhenoneofthekeyhazardsisVeryHigh.AHighratingforanyhazardisprimarilyintendedtoalerttheprescriptiondeveloperandtheoperationalstaffofahazardthatmayrequirespecialtreatmenttopreventproblems(manageandmitigatethehazard).Highcompactionhazardalsoresultsinmoreequipmenttrafficdisturbancetypesbeing“counted”1underFRPAdisturbancecriteria. The soil disturbancehazards alsohelp identify siteconditionsthataresuitableforconstructionofexcavatedandbladedtrails(skidroadsorbackspartrails),and/ortemporarilyexceedingsoildisturbancelevelsandrehabilitatingslopehydrologyandforestsiteproductivity.Thehazardsaredefinedbelow,includingbriefdiscussionsofwhytheyareofconcern.2

Soil Compaction Hazard

Soilcompactionistheincreaseinsoilbulkdensitythatresultsfromtherear-rangementofsoilparticlesinresponsetoappliedexternalforces.Soilpuddlingisthedestructionofsoilstructureandtheassociatedlossofmacroporositythat

1InBC,theterm“counted”isusedinreferencetosoildisturbancetorecognizethefactthatsoildisturbancetypesortheirseverityvarywithsoilsensitivitytodisturbance.Moredisturbancetypesareofconcernonmoresensitivesoils,andlessareofconcernonmoreresilientsoils(e.g.,sandysoils).Thenetresultisthatmoredisturbancetypesare“counted”towardsthetotalcumula-tiveallowablelimitonmoresensitivesoils.

2Soildegradationhazardratingkeysforsoilcompaction,displacement,anderosionarefoundinLandManagementHandbook47(Curranetal.2000)andtheForest Practices Code of British Columbia, Hazard Assessment Keys for Evaluating Site Sensitivity to Soil Degrading Processes Guidebook.The general BCMOF Web site where these and other FPC information can be lo-cated is: http://www.for.gov.bc.ca/ (look under legislation).

Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends Curran, Green, and Maynard


results fromworking the soilwhenwet.Organicmatter isoften incorporatedduringpuddlingandbecauseorganicmatterislighterthanmineralparticles,soilbulkdensitymaynotincrease;however,theotherpropertiesdescribedbelowarestillnegativelyaffected.ThescienceandrationalefortheBCcompactionhazardkeyarelaidoutinCarrandothers(1991).

Soilmoisturecontentisprobablythebestdeterminantofcompactionhazardatanygiventime.InBritishColumbia,thesoilcompactionhazardkeyranksthepotentialcompactionhazardbygroupingsoiltexturesthataremostsusceptibletostructuraldegradationfromcompactionandpuddling,andaremostlikelytoholdmoistureandremainwetforlongerperiods.Thesoilcompactionhazardkeyisatooltohelpwithplanningofanoperation,whilecarefulmonitoringofequipmenteffectsonthesoil,andhandtestsforsoilmoisturecontentarethetoolsthathelpguidetheoperation.

Soilcompactionandpuddlingareofconcernintimberharvestingoperationsbecauseofeffectsonrootsandsitewaterrelations.Compactedsoilshavehigherpenetration resistance thatcan impede rootgrowth.Compactedandpuddledsoils bothhave lower aerationporosity and lowerhydraulic conductivity andinfiltrationrates;however,insomecoarsertexturedsoils,compactionmayactu-allyincreasewaterholdingcapacity(thesesoilstypicallyhavelowercompactionhazardratings).

Loweraerationporosity results in reducedgasexchange thatcanadverselyaffectoxygen levels in the soil air; this reducesphysiologic functionof roots,whichinturncanleadtorootdieoffunderwetterconditions.Lowerhydraulicconductivityandinfiltrationratesofthecompactedorpuddledsoilcanresultinincreasedrunoffduringrainfallandsnowmeltevents.Thiscanleadtoincreasednetexportofwaterfromacutblock,whichcanaffectdownslopesites,naturaldrainagefeatures,andotherresourcevaluesduetoerosionandsedimentation.Increasedwaterexportalsomeanslesswatermaybestoredonsitetosupporttreegrowthduring summerdrought.Compacted soils canalso remainwetterlonger,therebyfurtheraffectingseedlingsbecausethesoilmaybecolderandhavepooraeration.

Monitoringoftraditionalspringharvestingonthreeash-capinfluencedsoilsinthesouthernRockyMountainTrenchnearCranbrookindicatedthatsignificantdeclinesinaerationporosityoccuredwhenevidenceofequipmenttrafficwasvisibleontheground(e.g.,wheellugmarksonthesoilorslightimpressionswithtrackgrousermarks) (Utzigandothers1992).Thesesiteswere typicalTrenchsoils:siltloamtosiltyclayloamtexturedsurfacesoilslowincoarsefragments,underlainbydensersubsoilswithmorecoarsefragments.

TheundisturbedsoilshadaerationporosityvaluesatorabovethethresholdrecommendedbytheUnitedStatesForestService(USFS)insomeofitspolicyforthePacificNorthwest(i.e.,15%at10J/kgwatertensionreferredtoinBoyer1979). Regardless of the severity of disturbance, aeration porosities were lessthan15% (fig.1). Effectson saturatedhydraulic conductivity (i.e.,water rela-tions)weresimilar(fig.2).Bulkdensityincreasedinasimilarbutoppositetrendtotheaerationporosityandsaturatedconductivity,aswouldbeexpected.Theconcernabouttheseeffectsishowextensivethemachinetrafficdisturbanceisonfullymechanizedharvesting.Onthethreesitesstudied,thecombinedtotalofthelightruts,5-cmruts,andmaintraildisturbancerangedfrom52to64%oftheentirecutblockarea,withlightermachinedisturbancecoveringfromabout30toover45%(fig.3).



Figure 1—Aeration porosity at 10 J/kg tension for two sample depths at three sites in the southern Rocky Mountain Trench near Cranbrook, BC (Utzig and others 1992). U (undisturbed), VL (very light ruts, <� cm deep), 1 (ruts � cm or deeper), HT (heavy [main] trails).

Figure 2—Saturated hydraulic conductivity for two sample depths at three sites in the southern Rocky Mountain Trench near Cranbrook, BC (Utzig and others 1992). U (undisturbed), VL (very light ruts, <� cm deep), 1 (ruts � cm or deeper), HT (heavy [main] trails), from Curran (1999).



TheseresultsareconsistentwithmonitoringstudiesofnearbysitesinnorthernWashington,Idaho,andMontana(Kuennenandothers1979;LaingandHowes1988,Svalberg1979). In theWashington study,basedon the literatureat thetime,LaingandHowes(1988)predicteda“conservativeestimateof35%volumereductionsoverthenextrotation”fordetrimentallycompactedareas(42%ofthecutblockareaintheirstudy).OnsimilarsitesinNorthernIdahoandMontana,Kuennenandothers (1979) suggested that changes in soil physicalpropertiesresultingfromcompactioncandecreasetheabilityoftreestocompetewithpinegrass.Itisnotclearwhetherthesetypeofeffectswouldberealizedonoursoils;however,intheabsenceoflong-termdatatothecontrary,weneedtocontinuetomonitortreegrowthonthesesites.LightcompactionisalsobeingstudiedaspartoftheNorthAmericanLong-termSoilProductivityStudy(LTSP).

Insummary, the implications forsitewaterstorage, runoff,and treegrowthareofconcernwhenrandomskiddingcausesthesetypesofdisturbances.Itisthereforeinferredthat,undercertainsoilconditions(e.g.,harvestingunderwetterthanoptimumsoilconditions),detrimentalcompactioncanoccurbeforesoildis-turbancecriteriaforrutsortrailsarereached.Harvestingstrategiesrecommendingdispersedskiddingtrafficneedtorecognizethisriskand“treadlightly.”Compac-tionisalong-livedphenomenon;naturalfreeze-thawandwet-drycycleshave

Figure 3—Aerial extent of soil disturbance at three sites in the southern Rocky Mountain Trench near Cranbrook, BC (Utzig and others 1992). LL (very light ruts, <� cm deep), HL (heavy [main] trails), 1&2 (ruts � cm or deeper), and L (very light and heavy, combined) from Curran (1999).



notbeenobservedtoamelioratemachine-inducedcompactionatdepth.Intheash-capsoillocations,wheresummerdroughtisoneofthefactorsmostlimitingtotreegrowth,andintheabsenceoflong-termdatatothecontrary,preventionofwidespread“belowtheFRPAdepthlimit”compactionisprobablythebestbetandcanbeachievedeconomically.

Soil Displacement Hazard

Soildisplacementisthemechanicalmovementofsoilmaterialsbyequipmentandmovementoflogs.Itinvolvesexcavation,scalping,exposureofunderlyingmaterials,andburialoffertilesurfacesoils.Threeaspectsofdisplacementcanproducesoildegradation:

• Exposureofunfavourablesubsoils,suchasdenseparentmaterial,gravellysubsoil,andcalcareous(highpH)soils.

• Redistributionandlossofnutrients. • Alterationofslopehydrology,whichcanleadtohydrologiceffects(discussed

undercompaction,above).

SoildevelopmentisoftenshallowandmanyofthenutrientsthatarelimitingtotreegrowthareoftenbiocycledandconcentratedintheuppersoilhorizonsthroughouttheBritishColumbiaInterior.Asimilaraffectoccursonshallowash-cap soils that overlay less fertile subsoils.Most of the soil nutrients areoftenconcentratedintheforestfloorandtop20cmofmineralsoil(table1).Therefore,wedon’twanttodisplacethisfertiletopsoilawayfromseedlings,orreducetherootingvolumeofthesevitaltopsoillayers.

Table 1—Typical nutrient distribution in British Columbia Interior soils.

Nutrients in kg ha–1 (% of total)Soil layer Nitrogen Phosphorus Potassium

Forest floor 14�0 (44%) 112 (�2%) 224 (7�%)0-20 cm 10�0 1� ��20-40 cm �20 � 2�Total ��20 1�� 0�

Forest Floor Displacement Hazard

Forestfloordisplacementisthemechanicalmovementoftheupperorganicmaterialsbyequipmentandmovementoflogs.Itinvolvesexcavation,scalping,mineralsoilexposure,andburialof theforest floor.Theeffectsof forest floordisplacement range from beneficial to detrimental, depending on site factors(e.g.mineralsoilcharacteristics)andhowfartheforestfloorisdisplacedfromtheseedlings.

Forestfloorstypicallyrepresentamajorcomponentofthenutrientcapitalonaforestsite.IntheBritishColumbiaInterior,itisnotuncommonfortheforestfloortocontainover50%ofthesoilnitrogenand80%ofthephosphorus(table1).GiventhatmanyInteriorsitesareconsiderednitrogendeficient,conservationoftheforestfloorisimportant.Ondeeperash-caporolder,richersoils,muchofthenutrientcapitaloccursinthemineraltopsoilandforestfloordisplacementmaybeoflessconcern.



Twoaspectsofforestfloordisplacementcanproducesoildegradation:

• Redistributionandlossofnutrients(e.g.chemicallyboundandunavailableinthemineralsoil,andaccelerateddecompositionoforganicmatter).

• Exposureofunfavourablerootingmedium.

AreviewofforestfloordisplacementandimplicationsfortreegrowthintheSouthernBritishColumbiaInteriorfoundthatwhiletherewereafewtrendsinsoilnutrientlevels,itwasdifficulttorelatedisplacementtoanynegativeeffectsontreegrowth(Hickling1997). IncooperationwithPopeandTalbotLtd.,weinstalledlong-termmonitoringplotsonvariousdisturbancetypesincludingsomeassociatedwithstumping(Hickling1998).

Most forestoperationswerewellbelow the forest floordisplacement limitsoriginallysetintheFPC,sodeterminingtheforestfloordisplacementhazardisnolongerofficiallyrequiredforharvestplanningandpermitting.However,useofthishazardinterpretationissupportedandrecommendedforplanningdispersedskiddingonsteeperslopes,rehabilitationofsoildisturbance,androotrottreat-ments.ForestfloordisplacementisalsomoreofaconcernoncalcareoussoilsduetothehigherpHofthemineralsoil

Surface Soil Erosion Hazard

Surfacesoilerosionisthewearingawayoftheearth’ssurfacebywaterandincludessplash,rill,andgullyerosion.Ithason-siteimpacts(soilloss,nutrientloss,lowerproductivity)andoff-siteimpacts(waterquality,sedimentation,habitatimpacts).Thesurfacesoilerosionhazardkeyfocusesonon-siteerosionandcon-servationofthefertiletopsoillayersneardevelopingseedlings.ThescienceandrationalefortheBritishColumbiakeywerelaidoutinCarrandothers(1991),andtheratingweightingstestedintheNelsonForestRegionbyCommandeur(1994),resulting inmodifications to the finalkeycurrently inuse.Otherassessmentsmaybeusedforhaulroaderosionandsedimentdeliverytostreams.Haulroadsandlandingsareofconcernbecauseerosionanddrainagediversionscanleadtosedimentationandstabilityproblems.Theyrequirecarefullayoutandattentiontoerosionhazardonhaulroadsandminimizingerosionandsedimentationduringconstructionandmaintenance.

Defining Soil Disturbance

Atechnicaldefinitionofsoildisturbanceisanydisturbancethatchangesthephysical,chemical,orbiologicalpropertiesofthesoil(Lewisandothers1991).Itisnotalwaysnegative.Foresterscommonlyprescribepurposefulsoildisturbanceas site preparation for seedling planting and establishment; these disturbancetypesareoftennotcountedinstandards(e.g.,underFRPAinBritishColumbia).Bycontrollinghowweharvestasite,wecancreatemore“sitepreparation”typedisturbanceandkeepmostofthepotentiallydetrimentaldisturbanceconfinedtotravelcorridors;thesemaintrailsmaythenberehabilitatedafterharvesting,asappropriate.Wheneverplanningsoildisturbance,thepreservationandrestorationofnaturaldrainagepatternsshouldbetheprimarygoal(necessaryrepetition).

Thestrategiesdescribedinthisdocumentstrikeabalancebetween“favourable”and“detrimental”disturbancebylimitingtheamountof“counted”soildisturbance.Regionally applicable soil disturbance standards recognize that some level ofdisturbanceisnecessarytopermitaccesstotimber.Counteddisturbanceusually



includesmaintrailsandruts/impressionsofcertaindimensions,andundersomeschemes(e.g.,FRPAinBritishColumbia)alsoincludewideordeepgougesintothesoil.Thosedevelopingandimplementingaharvestingstrategyneedtorecognizethatonmoresensitivesites,disturbancetypesthat“count”maybecreatedmoreeasilyandmaybecountedsooner(e.g.,inInteriorBritishColumbia5-cmrutsandimpressionsonHighandVeryHighCompactionhazard,asopposedto15cmonothersoils;whenErosion,Displacement,orCompactionhazardsareVeryHigh).Onsiteswithlowerhazardratings,lessdisturbancecategoriesmaybecounted.

Theactualeffectofagivensoildisturbanceontreegrowthwilldependonthemostgrowth-limitingfactorsonagivensiteandhowthesefactorschangeoverthecourseofarotation.IntheBritishColumbiaInterior,commongrowth-limit-ingfactorsinclude:competingvegetation,soilmoisture(droughtorexcess),soiltemperature,summerfrost,rootingsubstrate(volume),soilnutritionalproblems(e.g.,calcareoussoils),androotrot.Theneteffectongrowthwillalsodependonwhethersoildisturbancehasintroducedanewlimitation,suchasreducedsoilaerationfromcompaction.Long-termeffectscouldincludeincreasedsusceptibilitytoblowdownbecauseofpoorrootingindetrimentallydisturbedsoil.

Regional ecology guides often summarize common growth-limiting factorsfor various ecosystems (Braumandl andCurran1992), andamodelhasbeendeveloped for comparingdisturbanceeffectsongrowth-limiting factorswhendecidingonsitepreparationprescriptions(CurranandJohnston1992;Sachsandothers2004).

Regardlessoftheactualtreegrowtheffects,anumberofsoildisturbancetypesarealsoofconcernbecauseofpotentialeffectsonsiteandslopehydrologyandthepotentialfordownslopeimpacts.On-sitehydrologychangesaredifficulttostudybutweneedtoerrontheconservativesideconsideringthatmuchofBritishColumbiaisnotflatandsummerdroughtisoftenoneofthemostgrowth-limit-ing factorsonmanysites (effectsonhydrologymayconfoundtreegrowthonapparently“undisturbed”micrositesintreegrowthstudies).Similarhydrologicconcernshavebeenvoicedbyotherresearchersinthelocalarea(Kuennenandothers1979).

Synthesis of Above Knowledge and Principles in Our Forest Practices _____________________________________________

Machine-Based Practices

Forestharvest,sitepreparation,andfuelmanagementtreatmentsaremostcom-monlyaccomplishedthroughtheuseofmachinery.Inthecaseoftimberharvestorfuels,thismayoccurthroughaerial,cable,orground-basedequipment.Becauseground-basedharvestingtypicallycreatesthemostdisturbance,it isdiscussedbelowbuttheprinciplesremainthesamefortheothermethods.

Basedontheenvironmentalframeworkdescribedintheprecedingsection,agivenharvestingstrategyshouldmeetthefollowingfourrequirements:

1. Besitespecificandresponsivetothesoilsensitivitiesonsiteanddownslope. 2. Offerareasonableamountofindependencefromclimaticinterruptions,. 3. Incorporaterehabilitation,ifnecessary,tolowerdisturbancebelowguidelines. 4. Itmustinstillenoughconfidenceatalllevelsofapprovalandoperations.



Inthe1990sweworkedonanumberoftrialswithIndustryandDistrictstaff,toaddressconcernsaboutmanagingharvestingsoildisturbance.Trialshavead-dressedtreegrowthonrehabilitatedskidroads(DykstraandCurran1999),haulroads(Curran,unpublisheddata),andlandings(BulmerandCurran1999a).Memoswerecirculatedandaspecialpublication(Curran1999)summarizedsimplefieldtestsdevelopedduringoperationaltrialsofseasonalharvestingconstraints(i.e.,“howwetistoowet?”and“howmuchfrostisenoughfrost?”).Otherresearchtrialshavebeensuccessfulindemonstratingthefeasibilityofrehabilitatingsoildisturbance(BulmerandCurran1999b).Combined,thesetrialsweredesignedtotesttreegrowthonrehabilitateddisturbanceanddevelopstrategiestoreducethedependencyonweatherconditionsandreduceshutdownofoperationsduringwetterconditions.Researchandpracticalinnovationarestillongoing,andfurtherfieldguideswillbeproducedaswarranted(e.g.,wearedevelopingasimplersoiltexturekeyatthistime).

Basedonindustryinnovation,practicalexperience,andresearchtrials,wehaveidentifiedfourkeystrategiesthatwefeelmeettheabovecriteria:

a) closetrailspacingwithrehabilitation, b) closelyspacedtemporaryspur(haul)roadswithrehabilitation, c) combinationdesignatedanddispersed(random)skidding,and d) hoe-chucking,Interiorstyle(i.e.,forwardingtowiderspacedtrails).

Thesestrategiesmayormaynotincludefullymechanizedharvesting,eitherwithcut-to-lengthfeller-processorsandforwarders,orwithfeller-bunchersandgrappleskidders.Thestrategiesalsomayoffertheopportunitytoreducesitepreparationcostsbycreatingdisturbanceduringtheharvestingorrehabilitationphases.EachstrategyisdescribedinmoredetailinCurran(1999).OtherharvestingstrategieshavebeendescribedformeetingsoildisturbancestandardsundersiteconditionsinwesternWashingtonandOregonbyHeningerandothers(1997).Again,theobjective is tomatch equipment capabilities to site sensitivity to disturbance.Ground-basedequipmentmaybe restricted todesignated trailsorallowed totraveloverlanddependingonthesoilandclimaticconditions.

Studies on ash-cap influenced and similar soils in southern Interior BritishColumbiahaveshownthatlargeamountsofsoildisturbancecanoccurduringmechanicalrootremovalforrootdiseasemanagement(QuesnelandCurran2000;Curran, unpublished data). Tree growth responses to these disturbances varywithsitegrowthlimitingfactorsandovertime.OntwositesonsimilarclimateinsouthernBritishColumbia,stumpremovaltreatmentshaddifferingeffects(fig.4).Onanash-capinfluencedsoilatPhoenix,soildisturbanceeitherincreasedordidnotnegativelyaffecttreegrowth;whereasonasoilontheGatesCreeksitethathadmoreclay(12%versus4%),therewasaclearnegativetrendwithtreegrowthanddisturbanceseverity.Thelong-termgrowthtrendattheGatesCreeksiteisinterestingasitclearlydemonstratestheneedforlong-termtreegrowthresponsedata(fig.5).

Insect and DiseaseSome forest insects and pathogens are opportunistic organisms that cause

primarydamagetostressedhosttrees.Stressmayoccurduetosoildisturbanceeffectsontreegrowingenvironment,climatechangeresultingintemperatureormoisturestress,otherbioticorabioticenvironmentalfactors,ormultipleinteract-ingfactors.Interactingfactorsthatcontributetopestoutbreakarecomplex.For



Figure 4—Fifteen-year volume of Douglas-fir seedlings growing in different disturbance types on the Canadian Forest Service Gates Creek and Phoenix stumping trial sites in southern British Columbia, which are gravelly sandy loam textured with 12% clay at Gates Creek and 4% clay at Phoenix (Curran and others 200�a adapted from Wass and Senyk 1999).

Figure 5—Comparison of relative growth of Douglas-fir on a stump removal trial in southern British Columbia at �, 10 and 1� years since treatment. All data is relative to the undisturbed condition (Curran and others 200�a adapted from Wass and Senyk 1999).



example,largeareasofbarkbeetleinfestationsaresometimesattributedtoclimatechangeand/orrootdisease interactions (PartridgeandMiller1972).However,insectattackisalsodependentuponinherentdynamicsofinsectbehavior.ThefollowingtextfocusesonrootdiseaseorganismsinInlandNorthwest.

Environmental Factors Affecting the Distribution and Activity of Root Diseases

Biophysical Setting—Armillaria rootdisease (primarilycausedbyArmillaria ostoyae)andAnnosus rootdisease (causedbyHeterobasidion annonsum)arewidelydistributedinwesternconiferforests.Off-siteplantings,woundedtrees,andtreesgrowingoncompactedsoilsor inareaswithdrainageproblemsareparticularlylikelytobeaffectedbyArmillariarootdisease(GoheenandOtrosina1998;Wiensczykandothers1997).Douglas-firdominatedstands innorthernandcentralIdahoandnortheasternWashingtonexperiencesubstantialmortalityfromAnnosusrootdisease,especiallyondrysites (Schmittandothers2000).However,insoutherninteriorBC,Morrisonandothers(2000),foundsignificantlyhigherratesofArmillariasp.infectionondrysitesthanmoistorwetsites;andonceinfected,treesondriersiteswerelessabletoresistinfectionandweremorelikelytoshowabovegroundsymptoms.

Laminated root rot, (causedbyPhellinus weirii),occursmainly inhemlock,westernredcedarandgrandfirhabitattypesontheLoloNationalForest,butinfrequentlyinDouglas-firandsubalpinefirhabitattypes,whileArmillariaandAnnosumrootdiseasearedistributedmorewidely(Bylerandothers,1990).Hagleandothers(1994)similarlyfoundrootdiseasemostsevereingrandfirhabitattypes,andlowseveritydiseaseratingsoccurredmostoftenonDouglas-firhabitattypes.Declinesindiseaseseveritywerenotedafter160yearsasthemoresusceptiblespeciesdiedoutofthestand.TheysuggestthatgrandfirhabitattypesaremostlikelytosupportgrandfirandDouglas-firasseralandclimaxspecies,andthesearethemostsusceptiblespecies.

OntheLoloNationalForest,Bylerandothers(1990),foundhigherprobabili-tiesofArmillariarootdiseaseonDouglas-firhabitattypesonsoutherlyaspects.Moderateslopeshadahigherincidencethaneitherflatorverysteepslopes.

Soil Physical Properties—Inanotherstudy,Armillariaspp.infectionlevelsde-creasedwithincreasingclaycontent,whichiscorrelatedwithmoisture-holdingability (Wiensczykandothers,1997).This isconsistentwiththehazardratingsystemofFroelichandothers(1977).IntheWiensczykstudy,sandysoilsweremorehighlycorrelatedwithArmillaria spp.activity inblackspruce thanweresiltysoils,andasmoistureregimeincreased(basedonmottlesandgleying),Ar-millariaspp.frequencydecreased.ThismaybeduetoreducedgrowthofArmil-lariarhizomorphsinfinertexturedandmoistersoils,ortoimprovedtreevigor.Sand,largesoilpores,andhighbulkdensitywerealsopositivelycorrelatedwithAnnosumrootdiseaseinloblollypineplantations(Alexanderandothers,1975).It is thought that rapid infiltration in sandysoilsallowedeasy translocationofrootrotspores.Bakerandothers(1993)alsofoundthatlowsiltintheAhorizonwasanimportantpredictorofH. annosum infection.Blenisandothers(1989)alsofoundclayloamtobeleastfavorableforArmillariarootdiseaseandsandyloamthemostfavorable.Thepathogenisknowntobesensitivetolowlevelsofoxygenandhighlevelsofcarbondioxide.



Soil Chemical Properties—Armillaria ostoyaeinfectionlevelswerefoundtoincreasewithincreasingphosphorousintheAhorizon(Wiensczykandothers1997).However,phosphorousinash-capsurfacesoilsisoftenheldinunavailableformandmaynotlocallycontributetoinfection.Reducedphosphorousmaylimittreerootelongation,whichcouldreducethelikelihoodofundergroundcontactwithA. ostoyae.

Rishbeth(1951)foundH. annosuminfectionratesfromstumpstobelowerinacidthanalkalinesoils.Heattributesthistocompetingfungiinmoreacidsoils.Bakerandothers(1993)foundH. annosum infectionincidencetobelowerinacidsoils,asdidBlenisandothers(1989).

Soil Microbiology—Rootmicroflora,suchasActinomycetesandfungi(e.g.,Trichodermaspp.,Phlebiopsisspp.,Bjerkanderaspp.,Hypholomasp.,etc.),canhavefungistaticeffectsonrootpathogens(HagleandShaw1991;HoldenreiderandGreig1998;Nelson1964,1973;NelsonandThies1985,1986;Raziq2000).Ithasbeensuggestedthatmixedstandswithfewerpotentialhostspecies,andinterruptionofsuccessionwithshrubandothernon-susceptiblespeciesreduceH. annosum inoculum(JohanssonandMarklund,1980)bysupportingenhancedpopulationsofActinomycetes.ChapmanandXiao(2000)confirmedtheabilityofasaprophyticfungus,Hypholoma fasciculare,toout-competeA. ostoyaeonavarietyofnonlivingsubstrates,suchasstumps.VeechandBoyce(1964)alsofoundhigher levelsofsoil fungi,Actinomycetes,andbacteria thaninareasofhigherH. annosuminfection.Greig(1962)alsofounddevelopmentofAnnosum rootdiseasetobelowerinplantationsestablishedonareasformerlyoccupiedbyhardwoodsthanonsecond-rotationconiferplantations.This“diversityofsoilmicroflora” ishypothesized tobemore typicalofnaturaldisturbance regimesthanstandsaffectedbyfiresuppressionandemphasisononeortwosusceptiblecropspecies,likegrandfirandDouglas-fir.

Ectomycorrhizalfungiassociatedwithtreerootsareknowntobeimportantformoistureandnutrientrelationshipsofthehosttree(Harveyandothers1986,1987).Decayedsoilwoodpromotesthisassociation.Rootpathogensmayinteractdirectlywithmycorrhizaesothatbiomassandenergyreservesofallpartiesarereduced(Graham2001;Sharmaandothers1992),butsometimespathogeneffectsonthehosttreearereduced(Morinandothers1999).Thiscomplexinteractionsuggestsweneed tosustainacontinuoussupplyof theorganicmaterials thatsupporthealthymycorrhizalpopulations.

Relation to Properties of Volcanic Ash—Surface soils formed in volcanicashtendtobesiltyintexture,havehighporosity,andlowbulkdensity,andlowinherentnutrientstatus,andlownutrient-holdingcapacity(McDanielandothers2005).Theymayadsorbphosphorusandholditinanunavailableform.Acid-ityistypicallyslightlyacidtoneutral.Treerootsareoftenconcentratedinthevolcanicashlayer,suggestingthatrootcontactcouldbecommonanddistancefromstumpinoculationpoint to live rootwouldbeshort.Thiswouldmake iteasier for infections to spread. High moisture-holding capacity suggests thatdrought-inducedstressduringsummerswouldbesomewhatmitigated,butthatthiscapacitywouldbereducedbycompactionordisplacement.Volcanicashishighlycorrelatedwithgrandfir,cedar,hemlock,andsubalpinefirhabitatseries,andtoalesserextentwithDouglas-fir.



Management Effects—Fireexclusion,harvestoflesssusceptiblepineandlarch,anddeclinesinwhitepineduetoexoticblisterrust(Cronartium ribicola)haveallcontributedtotheincreaseinmoresusceptibleDouglas-firandgrandfir,andmoistureandnutrientstress,increasingtheprevalenceofrootdiseaseintherangeofvolcanicashsoils.Morestudesareneededtodeterminetheeffectsofpartialharvestandsoilcompaction/displacementonrootdiseaseinmanagedstands.

Climate Change, Root Disease, and Management on Volcanic Ash-cap Soils

Climatechangecanresultinmaturetreesthataremaladaptedtotheirenvi-ronment,whichcanincreasevulnerabilitytopathogens(AyresandLombardero,2000),aswellasotherdisturbanceslikefireorinsects.IntheInteriorNorthwest,increasing temperatures and reduced summer moisture (McKenzie and others2004;Moteandothers2003)increasestressontreesinmarginalsites(thinash-cap,compactedsoils),whichmaymakethemmoresusceptibletorootdiseases.Physiologicalmodelstopredicthowtreedefenseswouldalterwithclimatechangearelacking.Effectsofclimatechangeonrootdiseaseandcompetingorganismsarenotknown.

Firesuppressionandsubsequentlymoreseverefiresmayincreasetherateofrootdiseasebyprovidingmorefire-scarredtreewoundsasentrancepoints(OtrosinaandGarbelotto1997).Fireexclusionleadingtodominanceofsusceptibletruefirsandhighlevelsofrootdiseasewouldalsoleadtoincreasedsusceptibilitytofireandlargeinsectoutbreaks.Higherdensitystandsduetofireexclusioncouldincreasethelikelihoodofbelowgroundspreadofthepathogenfromtreetotree.Longerperiodsofhighheatanddroughtcouldsuppresssporegerminationandstumpcolonizationforlongerperiodsinthesummer,althoughBendz-HellgrenandStenlid(1998)foundnoeffectoftemperatureonstumpcolonizationbyH. annosum.

Management Opportunities:

• Limitmanagementinducedstressbyconfiningsoilcompactionanddisplace-menttolimitedareasandrehabilitatingthemafteruse.

• Provideconnectionsforspeciestomoveinresponsetochangedclimaticcontext(maintainingcontinuityofspeciesinspace,whileallowingformovement).

• Usespeciesanddensitymanagementtoallowforestspeciestousedistur-banceassteppingstonesformigration.

• Introduceandsustainspeciesresistanttorootdisease. • RootremovalhasbeenproposedtocontrolArmillariarootdisease(Roth

andothers2000),butsomestudieshaveconcludedthatinoculumremovalcannotbecompleteenoughtochangethedynamicsofrootdiseasedevelop-ment(Reavesandothers1993).Theassociatedsoildisturbance,particularlyinash-capsoils,islikelytohavedeleteriousphysicaleffects.

Theissueofsoilrestorationtorecoversuitablemoistureandairrelationshipsis complicated by other factors. Soil disturbance associated with roads, skidtrails,andprecommercial thinning (Hessburgandothers2001)wascorrelatedwithincidenceofblackstainrootdisease(causedbyLeptographium wageneri)insouthwestOregon.Alternatively,subsoilingtoalleviatesoilcompactionmayresultinrootdamageanddiebackofanyresidualtrees,attractingrootfeedingbeetles that carry black stain root disease. Kliejunas and Otrosina (1997) and



Otrosinaandothers(1996)foundhigherlevelsofergosterolinsubsoiledareas,whichindicatedhigherlevelsoffungaldecomposeractivity.Thiswasattributedtosoildisplacementandrootsevering.Thissuggestsmanagersshouldlimittheextentofcompactedareasasmuchaspossibleandavoidsubsoilingneartreestoavoidbothaboveandbelowgrounddamage.Stumpremovalcouldhavesimilareffectsinadjacentlivetrees.

Analysis of North Idaho Root Disease Trends in Relation to Soil and Site Factors

SueHagle (Pathologist,USDAForestService,Region1) ratedstandswithinrandomlyselectedsubcompartmentsforrootdiseaseactivityusingphotointerpre-tationonascaleof0to9(Hagleandothers2000).OnthethreeIdahoNationalForests(IdahoPanhandle,Clearwater,andNezPerce)analyzedhere,1,204plotswereavailable,but11ofthesedidnothavegeologicinformationand29didnothavesoilsurveyinformation.Thestandpolygonswereinteractedwithgeospa-tiallayersincludingsoilsurveymapunits,lithology,meanannualprecipitation,elevation,aspect,latitude,longitude,andslope.

Soilsurveymapunitswereclassifiedintofourclassesbasedonvolcanicashdepth:

1:Nodescribedvolcanicashinfluence 2:Thinormixedash 3:Andicsubgroups 4:Thickash(Andosols)

Wheresoil typevariedbyaspect,aspectwasused to refine theashdepthfactor.

Geologicgroupsweredevelopedbasedonliteraturedescribingassociationsbetweenrootdiseaseandrocktype(GarrisonandMoore1998;Mooreandothers2004).Thisprocesswascomplicatedbydifferentscales,notation,anddepthofdescriptionofavailablegeologicmaps.Wetriedtoidentifypotentialstrongas-sociationsbyspatialexplorationofrootdiseaseactivityandgeologicformation.Patternsthatappearedstronginoneareawerenotconsistentinotherareas.Theresultinggroupsusedare:

2 =Granitics,predominantlyCretaceous,butalsoJurassic(292samples). 3 =Recentmetamorphics(youngerthanBeltAge)(21samples). 4 =Beltagemetamorphics,butnotincludingBeltquartzitesdescribedunder

11.(666samples).Thesewereexpectedtohavehigherinherentfertility. 5 =Tertiaryandmorerecentsediments(3samples). 6 =SevenDevilsvolcanicsofTriassicandPermianage(20samples).Thesesites

wereomittedfromthisanalysisbecausetheyarethoughttobeanomalous.Theyhadveryhighrootdiseaseactivityratings.Trendsandsignificanceweresimilarwithandwithoutthesesamples.

7 =Undifferentiated,suchasglacialdepositsoralluvium(65samples). 8 =Othervolcanics(2samples). 9 =Limestonenosamples. 10 =Beltagesedimentsnosamples. 11 =Beltquartzites(MiddleWallacequartzites,StripedPeakformation,Revett

quartzite,andPrichardquartzite(94samples).Thesewereexpectedtohavethelowestinherentfertility.



EachstandwasadditionallyassignedtoamoistureandtemperaturegradientclassafterMcDonaldandothers(2000)usingthehabitattypeinformationas-sociatedwitheachstandpolygon:

Understory: Moisture RegimeNodata 0Drygrass 1Dryshrub 2Dryherb 3Moistherb 4Wetherb 5Wetfern 6Wetshrub 7

Overstory: Temperature RegimeNodata 0Coldfir 1Coolfir 2Cedarhemlock 3Douglas-fir 4Ponderosapine 5Pinyonjuniper 6

Thefollowingtablesandplotsdisplayexploratoryanalysisoftheassociationofrootdiseaseactivity(usingan8classrankingsystem)andcategoricalenvironmen-talvariables.Shownarethemedian,interquartilerange,extremes,andpossibleoutliers.Nopatternisapparentforaspectclassandrootdiseaseranking,

Root Disease and Ash Depth

Thinormixedashisassociatedwithhigherincidenceofrootdisease(table2).Lowrootdiseaseactivityassociatedwithareasofnovolcanicashareusuallyinverydrysteepslopesorpoorlydrainedareaswheresoilsareformedinmixedalluvium.

Soilswithnoashinfluencehavesignificantlylowerrootdiseaseactivity,butAndicsoilsandAndosolsdonotdiffersignificantly.

Table 2—Ash-cap depth as related to root disease ranking.

Ash Depth N

Mean RootDiseaseRanking* 95% C.I.

1 – None 25 2.2 1.5-2.9

2 – Thin or mixed 198 3.6 3.3-3.9

3 – Andic 247 3.2 2.9-3.4

4 – Andosol 638 3.0 2.9-3.2*See Hagle and others (2000) for detailed root disease activity scale.



Geologic Group

No strong trends were noted, however there were some differences among lithologic groups.

Recentmetamorphicsshowedgreaterrootdiseaseactivitythaninundifferenti-ateddeposits(table3).Thegreatvariabilityinrecentsediments(group5)suggestsaneedforfurtherrefinementofthisclass.Beltagemetamorphics(group4)showedrelativelylowrootdiseaseactivity,withnumeroussamples,andweresignificantlyless thangranitics, recentmetamorphics,andBeltquartzites.Undifferentiatedrocktypes(recentdeposits)alsoshowedlowrootdiseaseactivity.TheBeltAgequartzites,anticipatedtobenaturallylowinpotassiumandwithhighlevelsofrootdiseaseactivity,weresignificantlyhigherthanotherBeltmetamorphicsandundifferentiatedrocktypes,butdidnotdifferfromgranitics,recentsediments,orrecentmetamorphics.

Table 3—Influence of geologic group on disease incidence.

Geologic Group N


2 – Granitics 292 3.5 3.3-3.7

3 – Metamorphics(not Belt Age)

21 3.9 2.8-4.9

4 – Belt AgeMetamorphics/notquartzites

666 2.9 2.8-3.0

5 – Tertiary andmore recentsediments

3 4.3 .5-8.1

7 – Undifferentiated(recent glacialdeposits or alluvium)

65 2.9 2.5-3.3

8 – Other volcanics 2 3.5 NA

11 – Belt quartzites 94 3.5 3.1-3.9

*See Hagle and others (2000) for detailed root disease activity scale.

Root Disease and Forest

TheIdahoPanhandleNationalForesthadthelowestdiseaseranking,followedbytheClearwaterNationalForest,andthenNezPerceNationalForest(table4).Thesedifferencescouldbecausedbydriersoils,changesingeology,soilnutri-tion,orotherinherentsitephysical,chemical,orbiologicalproperties.

Table 4—National Forest and incidence of disease.

National Forest N


4 – Idaho Panhandle 639 2.7 2.6-2.9

5 – Clearwater 331 3.4 3.2-3.6

17 – Nez Perce 173 4.0 3.7-4.3




Root Disease and Potential Vegetation (Habitat Type Group)

PotentialVegetationisanindicatorofsoilmoistureandtemperatureregimesandconstrainswhethersusceptiblespeciesarelikelytooccurasseralorclimaxonthesite.Whenhabitattypes(Cooperandothers1991)aregroupedaccord-ingtoJones(2004),itisevidentthatthosehabitattypesmostlikelytosupportsusceptiblegrandfirorDouglas-firandshowhigherlevelsofrootdiseaseactivity(datanotshown).Theoccurrenceandseverityofrootdiseasedependsstronglyontheabundanceofasusceptiblehost.Siteswithalongerhistoryofdominancebysuitablehostspecieswilllikelyhaveaccruedhigherlevelsoffungalbiomass.DriergrandfirandDouglas-firhabitattypes,whicharemorelikelytosupportmoreponderosapine,showlowerlevelsofrootdiseaseactivity.Itisinterestingtonotethatsomeextremelyhighvaluesofrootdiseaseactivityareassociatedwithmoremoistcedarorwesternhemlockhabitattypegroups.Itispossiblethatthesesitesarecapableofveryhighlevelsofinoculumwhereseralwhitepinehasbeeneliminatedforlongperiods.

Moisture and Temperature Regime

UsingthemoistureandtemperatureindicesdefinedbyMcDonaldandoth-ers(2000),wecompareddiseaserankingagainstmoistureindicator(understoryassociation)andtemperatureindicator(overstoryseries).

Siteswithmoderatelydrymoistureregimes(dryshrub)hadthehighestrootdiseaseactivity,anddifferedfromdrygrassanddryshrub,butnotmoistherb(table5).ThismaybeduetothehighincidenceofsusceptibleDouglas-fironthesemoisturesettings.

Siteswithmoderatelywarmtemperatureregimes(Douglas-fir)hadthehighestrootdiseaseactivity,anddifferedsignificantlyfromcoldfirandponderosapine.Coolfirtemperatureregimeshadhigherrootdiseasethancoldfir,cedarhemlock,andponderosapine(table6).Again,thepresenceofsusceptiblehostspeciesishighlycorrelatedwiththesetemperatureregimes.

Table 5—Root disease ranking as related to understory moisture indicator.

Moisture Regime N


1 – Dry grass 12 2.2 1.1-3.2

2 – Dry shrub 89 3.4 2.9-3.8

3 – Dry herb 303 2.9 2.7-3.1

4 – Moist herb 734 3.2 3.1-3.3

5 – Wet herb 1 3 NA

6 – Wet fern 1 0 NA

7 – Wet shrub 1 1 NA




Table 6—Root disease ranking as related to temperature regime.

Temperature Regime N


1 – Cold fir 366 3.0 2.8-3.2

2 – Cool fir 153 3.6 3.3-3.9

3 – Cedar hemlock 528 3.1 2.9-3.2

4 – Douglas-fir 90 3.5 3.0-3.9

5 – Ponderosa pine 3 1.3 0-4.2


Association of Root Disease Ranking with Numeric Variables

Themostecologicallysignificantcorrelationsappeartobethatrootdiseaseactivity is positively associated with steep slopes, southerly latitude, westerlylongitude,potential forhost species (basedonhabitat typecover tables),anddecreasingannualprecipitation.

Conclusions _____________________________________________________Ash-capsoilsaresusceptibletodisturbance;schemestopredictcompaction,

displacement,anderosionhazardsareusefulinforestmanagementapplication.Whether more or less disturbance should be permitted on ash-cap soils is acontroversialtopicanditislikelymoreimportanttofocusontheindividualsitehazardsbecauseash-capsoilscanvaryconsiderablyintheirstateofweather-ing,texture,depthandinter-mixingwithothersoilmaterials.MachinetrafficcanbemanagedandasdemonstratedinBulmerandothers(thisproceedings),andmitigatedthroughrehabilitationinasetofharvest(machine-traffic)strategiesthatconsidersite.

Regardingrootdiseaseonash-capsoils,thispreliminarycoarse-scaleinves-tigation suggests some potential relationships among root disease (primarilyArmillaria in Idaho)and soil and site factors.The strong relationshipbetweenpresence of susceptible host and development of fungal biomass may be thestrongestcausalagent,andthesoilandsitefactorspromotethepresenceofthesusceptiblehost.

Thickerashsoilsofmorenortherlyareasarerelatedtohabitattypesthathis-toricallysupportedwhitepineandahigherdiversityoflesssusceptiblespecies.Thesemoremesicenvironmentsalsofillinwithotherspeciesrapidlyafterrootdiseasemortalityoccurs,sohigherlevelsofrootdiseaseactivityaremoredifficulttodiscern(Hagle,personalcommunication,2006).

Recommendations ______________________________________________Sustainablesoilmanagementonash-capsoilsneedstofollowprotocolsdeveloped

forallsiteswherebyanadaptivemanagement/continuousimprovementprocessneedstobesupportedbyresearch,bestmanagementpractices,andstrategiesthatincludealltypesofmonitoring(compliance,effectivenessandvalidation).



Developmentofacommonapproachtodescribingsoildisturbanceandsoildisturbancehazardswillgoalongwaytowardmoreeffectivesharingofmanage-mentexperiencesonash-capsoils.

Moreworkisneededonthelong-termeffectsofcumulativeaerialextentofsoildisturbanceandonsoildisturbancecategories torefine theseandhazardratingsystems.

For the root disease work, more site-specific evaluation of soil properties,standhistory,andgeologicparentmaterials,bothmineralogicalcompositionandweatheringstate,wouldhelptosortouttheserelationships.

Acknowledgments ______________________________________________TheauthorsthankDr.R.E.Miller,emeritusresearchscientistatUSDAForest

Service,PacificNorthwestResearchStationforhisreviewofthemanuscript,andSueHagle,pathologistforUSDAForestServiceRegion1forherhelpfuladviceandreviewoftherootdiseasepartofthispaper.

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Chuck Bulmer is a Soil Scientist, BC Ministry of Forests and Range, Vernon B.C. Mike Curran is a Soil Scientist, BC Ministry of Forests and Range, Nelson, B.C. Jim Archuleta is a District Soil Scientist, Dia-mond Lake District, Umpqua National Forest, Idleyld Park, OR.

Abstract Soilrestoration(sometimestermedenhancement)isanimportantstrategyforsustainingtheproductivityofmanagedforestlandscapes.Tephra-derivedsoilshaveuniquephysicalandchemicalcharacteristicsthataffecttheirresponsetodisturbanceandrestoration.Avarietyoffactorsreduceforestproductivityondegradedsoils.Site-specific informationonsoilphysicalconditions,organicmatter,andnutrientstatus is requiredforefficientsoil restoration,butonly limitedresearchisavailable tohelp interpretsuchinformationandguideefforts torestore tephra-derivedsoils.Basedonsite-specificconditions,reclamationtreatmentscanbeidentifiedtocontrolwater,tillcompactedsoils,restoreorganicmatter,andrevegetatedisturbedareas.Successfulreclamationinvestmentswillofteninvolvesimpletreatmentsfocusingonlowcostoptionssuchasdecompaction,topsoilreplacement,fertilization,andtreeplant-ing.Avoidingdifficultsitessuchthoseinhighelevationenvironments,wetareasorfinetexturedsoilsisrecommendedwherepossible,astreatmentstoovercomesuchproblemsarelikelytobeexpensiveandhaveuncertainoutcomes.Restorationefforts involcanic terrain likelyneed tobeaccompaniedbyprogramstomonitorthebeneficialeffectsoftreatmentsonforestproductivity,inrelationtotheircosts.

Restoring and Enhancing Productivity of Degraded Tephra-Derived Soils

Chuck Bulmer, Jim Archuleta, Mike Curran

Introduction

Soilrestoration(sometimestermedenhancement)isanimportantstrategyforsustainingtheproductivityofmanagedforestedlandscapes(Richardsonandothers1999),andecosystems(Cairns1999).Restoration techniquesplayaroleas (a)plannedactivities for improving theefficiencyofaccessingandharvestingtimberwhilemeetingsoilconservationgoals,or(b)ameanstorepairunanticipateddamagetosoilscausedbyharvesting,orwherepreviousmanage-mentapproacheshavebeensupersededbystrategiesthatreducetheneedforsoildisturbance,andallowrestorationofpreviouslydisturbedareas. Tephra-derived soils have unique physical and chemical characteristics that affect theirresponse to disturbance and restoration. Volcanic materials have undeveloped crystallinestructureandweatherrapidlyinhumidenvironments,producingsoilsthatarecharacterizedbyhighwaterholdingcapacity (Moldrupandothers2003)andcationexchangecapacity,


Bulmer, Archuleta, and Curran Restoring and Enhancing Productivity of Degraded Tephra-derived Soils

theabilitytostabilizesoilorganicmatter,andhighreactivitytowardsphosphate.InthePacificNorthwest,mountainoustopographyleadstostrongredistributionofashfallmaterialsthatwerelikelydepositedinfairlyuniformlayersthroughouttheselandscapes.StrongenvironmentalgradientsalsocreatediverseweatheringandpedogenicenvironmentsinPacificNorthwestforestsoils.Forthesereasons,theexpressionofandicsoilcharacteristicsshowsgreatvariationwithinlandscapes,creatingawiderangeofconditionsintephra-affectedsoils,andasimilarrangeof responses to soil disturbance and subsequent restoration or enhancementefforts.

In general, the goal of forest soil restoration is to recreate pre-disturbancegrowingconditions,sothattreegrowthratesonthereclaimedsoilwillapproxi-matethoseoftreesonundisturbedsoilsonsimilarsites.Effectivesoilrestorationemploystechniquesthatalleviategrowth-limitingconditionsonsitesthathavesuffereddegradingsoildisturbance.Degradedsoilsaredefinedhereassoilsthathaveexperienceddisturbanceleadingtoalossinproductivity.Forestproductiv-ityondegradedsoilscanbereducedbycompactionthatcausesplantrootstoexperiencelimitingconditionsofsoilmechanicalresistance,wateravailability,andaeration.Removalofsurfacesoillayersmaycausesimilareffectsbecauseorganicmattermaybedepletedfromthesite,orbecauseunproductivesubsoilmaterialsmaybeexposed.Degradedsoilsmayalsobemoresusceptibletoerosionwhichcancausefurtherlossofnutrientsandorganicmatterthatareessentialformaintainingsiteproductivity.Erosioncanalsocauseseriousoff-siteconsequencesforaquaticandterrestrialsystems.

Site-specificinformationonsoilphysicalconditions,organicmatter,andnu-trientstatusisrequiredforefficientsoilrestoration,butonlylimitedresearchisavailabletohelpinterpretsuchinformationandguideeffortstorestoredegradedsoilsderivedfromtephra.

Restorationtechniquesaimedatcontrollingerosioninclude(a)thoseaimedatstabilizingsoilssuchassloperecontouring,(b)thoseaimedatmanagingwatersuchasditchingoroutslopingand(c)thoseaimedatpreventingsoildetachmentsuch as revegetation. For compacted soils, tillage is often required to restoreconditionsconduciveforproductiverootgrowth.Restorationoforganicmatter,where appropriate, may be accomplished through replacing displaced topsoilmaterials,bymulchingwithorganicmaterialssuchasloggingdebris,orthroughthesoilbuildingactionofseededcovercrops.

Thismanuscriptoutlinestheroleofsoilrestorationinmaintainingtheproduc-tivityofmanagedforestlandscapes,reviewstheprinciplesthatgovernhowtheuniquecharacteristicsoftephra-derivedsoilsaffectrestorationplanninginvolcanicterrain,discusseshowinformationavailablefromelsewhereappliestoreclamationtechniquesinvolcanicterrainofthePacificNorthwest,andprovidesmanagementrecommendationstoguiderestorationandenhancementefforts.

Soil Restoration to Conserve and Enhance Productivity in Forested Landscapes _____________________________________________________

Minimizingdegradingsoildisturbance(Page-Dumroeseandothers2000)isanimportantfirststeptoensurethatsoilsaremaintainedinaproductivecondition,andthatforestmanagementissustainable.ThroughoutNorthAmerica,regula-torysystemsareinplaceforpreventingsoildegradationduringforestharvesting,


Restoring and Enhancing Productivity of Degraded Tephra-derived Soils Bulmer, Archuleta, and Curran

accessdevelopment,andothermanagementactivities(Powersandothers1998;USDAForestServiceStandardsandGuidelines2521.1and2521.2;CCFM2002;BCMinistryofForests2001).Thesesystemsgenerallyspecifysitespecificlimitsfordefinedformsofdegradingsoildisturbance,andmayalsoprovideincentivesforrestoringsoilsthathavebeendegradedbyforestmanagementactivities.

InBritishColumbia,soilconservationpolicyallowsmoresoildisturbanceonsiteswithlowsensitivitytosoil-degradingprocesses(BCMinistryofForests2001).InthenorthwesternUnitedStates,higherintensityofsoilcompaction(i.e.20%increaseinbulkdensity)isconsideredacceptableonvolcanic-ashderivedsoils(Powersandothers1998),comparedtothosedevelopedonotherparentmaterials(maximum15%increase).Thesedifferencesrecognizethatmanyundisturbedtephra-derivedsoilshavelowbulkdensity,butmayalsoimplythattheyarelesssensitivethanothersoilstomodestchangesindensity.Tephra-derivedsoilsmayalsoresponddifferentlythanotherstoreclamationtreatments.

Restoringdegradedsoilsimprovesforestproductivity.Onaccessstructuresthatarenolongerneeded,restorationandreforestationincreasesthelandbaseavailableforgrowingtrees,andcantherebyincreasefuturetimbersupplies.Onareasthathavesuffereddegradingsoildisturbance,restorationcanimproveestablishmentsuccessandproductivityofplantedtreescomparedtoareaswheresoilsareleftinadegradedstate.Achievingfullbenefitfromsoilrestorationpracticesdependsonthedevelopmentofcost-effectivereclamationtechniques,andtheirapplica-tiontositeswherethecostofreclamationwillbeoffsetbyimprovedproductivityfromthereclaimedlands(Richardsonandothers1999).

Reclamationworkshouldbesubjected tocostbenefitanalysis thesameasanyothermanagementactivity.Suchanapproachavoidswrongly thinkingofrehabilitationasanintrinsicallygoodactivity,wherethetruecostsofreclamationworkcanbediscountedorignored.Costsofrestorationworkincludedollarcosts,diversionofscarceresourcesfromotheractivities,consumptionoffossilfuels,andrisktoworkersorproperty,alongwithpotentialnegativeconsequenceswhichmaynotbeanticipatedsuchaswaterdiversion,erosion,slopefailure,andweedinfestation.Atthesametime,thepotentialbenefitsofreclamationworkmayalsobeunderstatediftheanalysisisrestrictedtraditionaleconomicmeasures(dollarcostsonly),orifinappropriatediscountratesareappliedtotimberproduction.Thesocialandenvironmentalbenefitsofcarryingoutreclamationactivitiesmayhavebeenneglectedinthepast,butrecentevaluationshaveshowntheimportantrolethathealthyecosystemsplayinmaintainingeconomiesandsocieties(Hillel1991).Suchconsiderationsarelikelytobecomeevenmoreimportantasglobal-izationandpopulationgrowthexertincreasedpressureonnaturalenvironmentsallovertheworld.

Ingeneral,giventhealmostuniversalscarcityofresources,theuncertaintyofcostbenefitanalyses,andtherisksassociatedwithundertakinganyactivitythatimposessignificantdisturbancetoanaturalsystem,aprudentapproachwouldfocusreclamationeffortsonsiteswheresimpletechniqueshavebeenshowntohavesuccess.Treatmentofhighrisksitesanduseofexpensiveorexotictreatmentsare likelybest left to special situationswherepotentialvaluesarehigh, socialfactorswarrant,orwheresucheffortsaretreatedasanoperationaltrialorwheredetailedmonitoringwillimproveouroverallunderstandingofrehabilitationanditsroleinforestmanagement.



Characteristics of Tephra-Derived Soils as They Affect Growth-Limiting Conditions and Restoration Efforts ________________________________

Variationinsoilpropertiesandgrowth-limitingfactorsintephra-derivedsoilsarisefrom(a)ecologicalcharacteristicsofthesiteassociatedwithclimate,topog-raphy,parentmaterials,andvegetation,(b)chemicalandphysicalcharacteristicsofthetephraasitwasdeposited,and(c)redistributionandalterationoftephrainthelandscapeinresponsetotopography,moistureetc.

StrategiesforreclaimingsoilswithouttephrainfluencehavebeendevelopedinthePacificNorthwestandelsewhere,andspecifydifferentapproachesforarangeofsoilsindiversegeographicsettings.Theapplicabilityofthesetotephra-derivedsoilsdependsonthedifferencesinsoilpropertiesbroughtaboutbythepresenceoftephra.Somequestionstoconsiderinclude:

• Havenaturaldepositionsoftephraledtoimprovedsoilfertilitybyprovidingasupplyofreadilyavailableinorganicnutrients?

• Whatistheweatheringstateofthetephra?Tephramaterialsweatherrapidlyinhumidsurfaceenvironments,butinthePacificNorthwesttherearemanyexamplesofrelativelyunweatheredmaterialseitherbecauseofdryclimatesorshortdurationofweatheringsincedeposition.

• Whatistheparticlesizeofthetephramaterials?InthePacificNorthwest,variationinphysicalandchemicalpropertiesastheyaffectplantgrowthprimarily results from particle size effects (including distance from thesource)andpostdepositionalalterationincludingorganicmatterretentionandweathering.

• Foragivenparticlesize,tephra-derivedsoilstendtohavephysicalcharac-teristics(i.e.waterholdingcapacity;specificsurface;organicmatterreten-tion)thatreflectthoseofothersoilmaterialswithfinertexture(i.e.sandytephramaterialsmaybehavemore like loamsderived fromotherparentmaterials).

Morphological Characteristics of Tephra-Derived Soils

Tephra-derivedsoilsincludethosewhereminoramountsoftephrawerede-positedtosoil,butarenolongerdiscernableasadistinctlayer.Inothersoils,adistinctlayeroftephraispresentasan“ash-cap’ofvaryingdepth(fig.1).Finally,somesoilsmaybeexclusivelyderivedfromvolcanicmaterialstothedepthofrooting,withlittleornoinfluencefromotherparentmaterialsonthevegetation.Manysoilswilldisplayintermediatecharacteristicstotheseidealizedcategories,especiallywheretephralayersbecomeintermixedwithsubsoilsduringconstruc-tionanduseofaccessstructures.Dependingontheproportionoftephra,andcharacteristicssuchasparticlesize,specialconsiderationsmayormaynotbeneededwhendevelopingreclamationstrategies.

Physical Characteristics of Tephra-Derived Soils

The presence of weathering products with highly reactive surfaces lead tothecommoncharacteristicsnoted forweatheredvolcanicmaterials, includinghighwaterretention,organicmatterstabilization,andwelldevelopedaggregatestructure.Thecharacteristicsareinter-relatedasorganicmatterispartlystabilizedbecauseofthesurfacereactivity,whilethepresenceoforganicmatterresultsin



additionalreactivesurfaces.TheexpressionofAndiccharacteristicsdependsonthedegreeofweatheringofthematerial.

Akeycharacteristicaffectingreclamationisthelowbulkdensityobservedinmanytephra-derivedsoils,owinginparttotheirlowparticledensitybutalsotothetendencytodevelopwellaggregatedstructures.Millerandothers(1996)foundthatevenafterasubstantialincreaseinbulkdensityofashderivedsoilsincentralWashington, the bulk density was still less than 1000 kg m–3. For this reason,thresholdvaluesforgrowth-limitingconditionsneedtobedeterminedspecificallyforashderivedsoils,ratherthanusingvaluesderivedforothersoils.

Figure 1—Ash cap overlying ultramafic soil material in the Shulaps Range: interior British Columbia.



Relationshipsbetweensoiltextureandmanagementimpactsreflectthevariableeffectsofashcharacteristicsandsoilenvironments.Forexample,poorlycrystallineweatheringproductsactasacementtocreateverystableaggregatesinAndisolsthatoccupywetsites.Also,theweatheringproductsofvolcanicparentmaterialshavehighsurfaceareacomparedtotheclaymineralsfoundinmostothersoils(Moldrupandothers2003).Inaddition,tephraparticlesoftenconsistofporousandfragilematerials,socoarse-grainedtephrasoilsareoftenlessresistanttofracturecomparedtonon-tephrasoils,andparticlesizedistributionmayshifttowardsfinersizefractionsfollowingmechanicaldisturbance(SahapholandMiura2005).

Tephra-derivedsoilsretainlargeamountsofwatercomparedtosoilsderivedfromotherparentmaterials.Conversely,theyarealsosubjecttochangesupondrying,whichcanincludethedevelopmentofwaterrepellency(Poulenardandothers 2004) and irreversible structural collapse (Poulenard and others 2003)whichismostlikelyforsoilsformedinwetenvironments(Shojiandothers1996).Inconsideringtheimpactofthischaracteristicondisturbanceandreclamation,thehighwaterretentionmayleadtoasoilwithlowbearingstrength,andhighsusceptibility toruttingwhenwet. Itmayalsomaketillageoperationsdifficultwhensoilsaremoist.Despitethis,thematerialsareexpectedtoprovideagoodgrowingmediumforplantroots,especiallyonmesicsites.

Unweatheredtephramaterialsareoftennon-cohesiveandpronetoerosionbywindandwater(BasherandPainter1997;ArnaldsandKimble2001),andthissusceptibilitymaylastforsometimeinunvegetatedareas.Forthisreason,plan-ningshouldconsidermeasuresforrapidrevegetationofexposedtephramaterialsresultingfromdisturbanceandreclamation.Tephra-derivedmaterialswithcoarseparticlesizeshavealsobeenusedasawaterconservingmulch(Tejedorandothers2002,2003).Thischaracteristicmayalsopresentchallengeswhenconsideringtheseedbedcharacteristicsofcoarse-texturedtephrasoils.

Theuniquephysical conditionsprovideboth challenges andopportunities,andbothneedtobeconsideredwhenplanningrestorationtreatmentsfortephra-derivedsoils.

Chemical Characteristics of Tephra-Derived Soils

Thechemicalcharacteristicsoftephravarydependingonthegeologicenviron-ment,andthesecharacteristicsareinheritedbythesoilsderivedfromvolcanicmaterials.Ingeneral,thecompositionoftephramaterialsinthePacificNorthwestaresimilartothoseofrhyolite,whichisexpectedtoprovideadequatesuppliesofmineral-boundplantavailablenutrientsinunweatheredormoderatelyweatheredsoils.Theweatheringproductsofvolcanicashhaveahighaffinityfororganicmatter,andthischaracteristicaccountsformanyoftheuniqueproperties,includ-ing high cation exchange capacity, and high availability of organically boundplant nutrients. Anion exchange capacity derives from the creation of poorlycrystallineoxidesofFeandAl,andalsofromshortrangeorderaluminosilicateslikeallophane.Theanionexchangecapacityaccountsforthehighreactivityoftephra-derivedsoilstophosphate.Despitethesefeatures,recenttephradepositswhichcharacterizemuchofthePacificNorthwestmayhavesimilarfertilitytootherparentmaterials(McDaniel,thisproceedings).

Thepresenceoflargeamountsoforganicmatterinweatheredashdepositsisexpectedtoleadtosoilmaterialsthatareresilienttodisturbance,butunweatheredmaterials incoldordryenvironments,mayhavelowlevelsoforganicmatter.



Reclamationplanningshouldconsidertheneedfororganicmatterandnutrientadditionsinconsiderationofsoilconditionsandforestproductivityinundisturbedsoilsonsimilarsitetypesinthearea.

Planning Considerations for Restoring and Enhancing Productivity of Tephra-Derived Soils

Theuniquechemicalandphysicalcharacteristicsofsoilsderivedfromtephraplayanimportantroleindeterminingwhattreatmentsshouldbeconsideredforrehabilitating or enhancing a degraded soil. To develop the most appropriaterestorationapproach,thefollowinggeneralquestionsneedtobeansweredbycollectingfieldinformation:

1. Isthesoildegradedtothepointthatforestproductivityorothervaluesarelikelytobesignificantlyaffected?

2. Whatgrowth-limitingconditions(e.g.compaction,organicmatterloss)orotherissuessuchaserosion,sedimentdeliverytostreams,orvisualconcernsarepresentthatrequireamelioration?

3. Aretheresiteconditionsorotherfactors(e.g.culturalresources)thatprecludeorfavortheuseofonerehabilitationtechniqueorcombinationoftreatmentsoveranotherforaddressingthegrowthlimitingfactor(s)?

4. Areproventreatmentslikelytoincreasesiteproductivitytoanextentwheretheassociatedcostswillbereturned?

SeveralresearcheffortsinnorthwesternNorthAmericaandelsewherehaverecentlyfocusedonevaluatingtheeffectivenessofcommonlyusedsoilrehabilita-tiontechniques.Althoughresearchspecificallyaddressingdegradedtephra-derivedsoilsinthePacificNorthwestislimited,theprinciplesgoverningthesuccessorfailureofsuchworkareexpectedtobesimilartothosefromelsewhere,andondifferentsoiltypes.

Fortephra-influencedsoilsincoastalWashington,Millerandothers(1996)ob-servedthattreesoncompactedskidtrailsweregrowingatthesamerateastreesinundisturbedsoilsandtrailswheresoilsweredecompacted.Theyconcludedthatsitespecificfactorsdeterminedtheresponsetosoildisturbanceandrehabilitation.Whereclimatic factorswere favorable,andsoilpropertiesofcompactedsoilsremainedwithinthresholdsforgrowthlimitingfactors,productiveforestscoulddevelopondisturbedsoils.Forthetephra-influencedsoilsstudiedbyMillerandothers(1996),despitea50percentincreaseinbulkdensityafterharvestandvaluesofbulkdensitythatwere20percenthigherafter8years,thedisturbedsoilsstillhadbulkdensitybelow1000kgm–3.Partlybecauseoftheresults,theauthorsconcludedthat therelationshipbetweenpre-disturbanceandpost-disturbancebulkdensity,whichhasbeenusedasanindicatorofsoildegradationintheUnitedStates,wasnotagoodpredictorofproductivityeffects.

Thecomplexprocessesaffectingseedlingresponsetodisturbanceandrehabilita-tionwerefurtherillustratedbyresultsfromPriestRiver,Idaho,wheresoilcompactioneffectsontreerootgrowthwerestudiedonasoilderivedfromMazamatephra.Douglas-firandwesternwhitepineseedlingsgrowingincompactedsoilsforoneyearhadfewernonmycorrhizalroottipscomparedtosoilswithoutcompaction(Amaranthusandothers1996).EctomycorrhizalroottipabundanceanddiversitywasreducedbycompactionforDouglas-fir,butnotwesternwhitepine.Despitetheseresults,seedlinggrowthresponsewasnotsignificantlyaffected.Thusthe



initial responsetocompaction,andtheneedforrehabilitationtreatments,notonlyvariesfordifferentsoilanddisturbancetypes,butalsomaydependonthetreespeciesundermanagement.

RecentresultsinBritishColumbiaonarangeofsoiltypesandclimaticcondi-tionshaveshownthatrelativelysimplerehabilitationtreatmentssuchassubsoil-ingfollowedbyplantingwithlodgepolepineoftenproducewell-stockednewforests (Plotnikoffandothers2002;BulmerandKrzic2003),butonwetsites,fine-texturedsoils,orwheretopsoilretrievalandreplacementwerenotcarriedout, growth ratesmay lag thoseof undisturbed areasof adjacent plantations.LodgepolepineisoftenplantedonrehabilitatedsitesinBritishColumbiaowingtohighsurvivalratesandrapidearlygrowth.Incontrasttothepreviousresults,soildecompactionwithout treeplanting led tounsatisfactorystockingon100sitesinBC’ssoutherninterior(BulmerandStaffeldt2004),indicatingthatnaturalregenerationshouldonlybereliedonasareforestationstrategyaftercarefullyevaluatingtheavailabilityofaseedsource.

Theseresearchstudiesshowthatitisdifficulttogeneralizewhenpredictingtheresponsetodisturbanceandrehabilitation.Site-specificinformationisessentialfordeterminingwhichresearcheffortsandconclusionsapplytoaparticularsite,andthereforewhichcourseofactionislikelytobemostsuccessfulandcost-effective.Thefollowingcriticalsitefactorscanaffecttheresponsetosoildisturbanceandrehabilitationonaparticularsite:

• Climatic conditions suchas temperatureandannualwaterdeficitaffecttherootingcharacteristicsoftrees,andtheextenttowhichtheyarelimitedbymoistureavailability,coldtemperatures,shortgrowingseason,orotherfactors.

• Slope characteristics and surface drainage patternsaffectthepotentialforerosionorslopefailurethatcouldaffectresourcesonandoffthesite.

• Soil texture and tephra influence affect the response of the soil to thedisturbance and subsequent rehabilitation treatments because fine tex-turedmaterialshavelowstrengthwhenwetandarehighlysusceptibletocompaction,whiletheporesystemincoarse-texturedmaterialsisgenerallyresistanttocompaction,andlesslikelytosuffersoildegradationassociatedwithmachinetraffic.

• Moisture regimestronglyaffectsthetreegrowthlimitingfactors,andthelikelihoodofrealizingsuitableconditionsfortillageequipment.Wetsitesinparticularoftensufferincreasedsoildisturbancebecauseoflowsoilstrength,andrestorationeffortsfacechallengesbecauseofpoorsoilstructureresult-ingfromtillageofwetsoils.

• Presence of unfavorable subsoilsandtheextenttowhichsurfacesoildis-placementhasexposedthemormayforceplantrootstogrowinthem.

• Rooting depthinundisturbedsoils,potentialrootingdepthonthedisturbedsite,andthedepthofsoildisturbanceaffecttheresponseoftrees.

Theexpectedlossofforestproductivityifthesitewasleftaloneneedstobebalancedagainstthebenefitsofinterventiontoimproveconditionsonthesite.Incaseswheretheexpectedbenefitsaresmall,notreatmentwouldbeindicated,andplantedtreescouldsimplybemonitoredtoevaluatetheneedforfertilizerinputsorotheractivitiestomaintaingrowthratesatdesirablelevels.Insuchcases,site



productivitymaybeslightlylowerthanifsoildisturbancehadnotoccurred,butthelossinproductivitymaybesmallcomparedtocostofrestorationtreatments.

Insummary,reclamationtreatmentswilllikelydeliverthemostbenefitwhen:

• Climaticandothersiteconditionsfavourproductivetreegrowth • Severesoildisturbancewilllikelypreventseedlingestablishmentandsig-

nificantlyreducegrowthwithoutintervention • Provenandrelativelyinexpensivetreatmentssuchasdecompaction,topsoil

replacement,andrevegetationareappliedtomesicsiteswithmediumandcoarsetexturedsoils

• Difficultsites,wetareasandfine-texturedsoilsareavoided,astreatmentstoovercome these challenges are expensive and benefits unproven.

Restoration Treatments and Unique Aspects of Their Application to Tephra-Derived Soil ______________________________________________

Where soil disturbance is likely to reduce tree growth to an unsatisfactorydegree,andtreatmentsareindicated,abasicapproachtorehabilitationwouldinvolveattemptingtocreatesiteconditionsapproximatingthoseofundisturbedsoilsonsimilarsites inthearea,eventhoughthismaynotalwaysbepossible(e.g.wheresurfacesoilshavebeendisplacedandtheirretrievalisnotfeasible).Theconditionsonundisturbedsiteslikelyreflectwhatisconducivetoproduc-tiveforestgrowthinthearea.Todevelopacosteffectiveplanforimplementingreclamationtreatments,thereisaneedtoconsider:

• Theextenttowhichconditionsonthesiteareexpectedtoexceedthresh-oldsofgrowthlimitingfactorssuchasaerationporosity,soilmechanicalresistance,wateravailability,andnutrientcontent.

• Availabilityofdisplacedsurfacesoilthatcouldberetrievedandnatureofsurfacesoilsinnearbyundisturbedsoilsonsimilarsites

• Stones,stumpsorotherfactorsthatmayaffecttheoperationofequipment • Presenceofexistingvegetation,andlikelyseedsourcesforpreferredcrop

treesandotherspeciestobere-establishedonthesite • Expectedwildlifeorcattleusethatmayaffectthesuccessofreforestation

orrevegetationefforts

Basedonsite-specificconditions,reclamationtreatmentscanbeidentifiedtoaddresseachoffourobjectives.

Managing Water and Preventing Erosion

Watermanagementanderosioncontrolisthefirststepinreclamationplanning.Withoutastablesubstratethatisfreeoferosion,thebeneficialeffectsofrestorationtreatmentscouldbedestroyedbyremovaloforganicrichsurfacesoillayers,orbyexposureoflessfertilesubsoils.Inaddition,thehighcostsofpotentialoff-siteeffectsonwaterquality,fish,andpropertyrequirethatwateranderosioncontrolisgivenhighestpriority.Sitewatermanagementisalsoessentialforcorrectingdetrimentaleffectsofsoildisturbanceonthesoildrainageclassandmoistureregime.

Water management may be as simple as building a ditch to divert surfacewateraway froma roador landing,orcould involvemoreexpensiveoptionssuchassloperecontouringdesignedwithinternaldrainagetorestoretheflowofsubsurfacewater.

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Erodibilitymayberelatedtopoorcohesionofrecentlydepositedtephrama-terials,highwaterretention,andlowinternalstrengthofdeposits.Thesefactorsmaybeoffsetbyhighporosity.Thecharacteristicsofthesubsoilsandothersiteattributesneedtobeconsideredbeforeselectingtreatments.

LocalizederosionwasobservedinDiamondLakeDistrict,UmpquaNationalForest,whensurfacewaterflowpatternsweredisturbedbycompactionofdeeppumicesoils,routingwatertotheedgeoftheunit.Routedwateraffectedresidualtopsoilleftpost-harvest,and,wherecompactionenduresforlongperiods,waterroutinganderosionwouldcontinueintothefuturewithouttillage.

Treatmentstocontrolerosioninclude:

• outslopingdecompaction • sloperecontouring • diverting/managingsurfacewater • revegetation

Wherewatermanagement,erosion,slopestabilityissuesdonotposesevererestrictions,thenextstepistoproceedwitheffortstorestoresiteproductivity.

Tillage to Restore Soil Physical Conditions

Forcompactedsoilswithhighsoilstrengthorthosethathavesuffereddeterio-rationoftheporesystem,restoringsoilphysicalconditionsisanessentialpartofreclamation.Compactionaffectstheporesystemmostlybyreducingthenumberoflargepores.Thisleadstoincreasedwaterretentionandreducedinfiltration,andmayleadtosoilswithinsufficientairforplantroots.

Therearereasonstobelievethattreesgrowinginsomesoilsrichinvolcanicashmayresponddifferentlytocompactionthanforotherparentmaterials.Thehighlydevelopedaggregatestructureofweatheredanddevelopedsoilsderivedfromvolcanicmaterialsinotherareashasbeenwelldocumented,suggestingthatstableaggregatesinsuchsoilsmaysurvivethecompactionprocess,andprovidestabilityforlargepores.ForthePacificNorthwest,recenttephradepositslikelyhaverelativelystablemacrostructurewhereparticlestrengthishighenoughtoresistparticlebreakage.Onmesicanddrysites,thesecharacteristicsmayleadtoasoilthatisabletowithstandcompactionandstillprovideaproductiveenviron-mentforplantroots,and/oronethatisabletonaturallyregeneratesoilconditionssuitableforproductiveforestgrowthfollowingdisturbance.Despitethis,somespecificchallengescouldinclude:

• Water retention:Onwettersites,thehighwaterretentivityoftephrasoilsmayleadtosimilarproblemsasidentifiedforfine-texturedsoils,andcouldbe especially problematic in low-lying landscape positions. The majorproblemswouldincludeexcessivesoilwater,andlackofaeration.

• Particle breakage:Somevolcanicmaterialsaresusceptibletoparticlebreak-agewhendisturbed,whichincreasestheproportionoffinesintheparticlesizedistribution.ParticlebreakagemaybeafactorinpoorperformanceofregenerationonsomesitesinOregon.

• Irreversible drying:Cementationmayleadtomassivestructurewithhighsoilstrengthsthatplantrootsareincapableofpenetrating.AlthoughthisphenomenonisnotexpectedtobewidespreadinthePacificNorthwest,it

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couldaffectresultsinlowlyinglandscapepositionswithweatheredsoilsandwheresoilstructurehasbeendestroyed(puddling)byrepeatedmachinetraffic,andwheresitesaresubjecttooccasionaldryinginsummer.

Wheretillageisrequired,avarietyofimplementsareavailable,includingwingedsubsoilers,rockripper,excavatorswithbrushrakes,mulchingheads,orcustomattachmentssuchasthesubsoilinggrapplerakeandsubsoilingexcavatingbucket.Thebestimplementforthejoblikelydependsonfactorssuchasrequireddepth,soilstrength,waterstatus,andlogistics(e.g.availabilityofprimemovers).

Anexampleofanimplementthatwaspurpose-builtfordecompactingsoilsinvolcanicterrainisthesubsoilinggrapplerake,whichwasdevelopedandusedintheDiamondLakeRangerDistrict, UmpquaNationalForest(ArchuletaandKarr2004).Thisimplementisagrapplerakefittedwithsubsoilingshanksandwings. Itwasdesigned tomitigateeither legacycompactionornewlycreatedharvestimpacts,andisbestemployedwhenusedinconcertwithanongoingactivity,suchaspost-harvestslashreduction.AtDiamondLake,thecombinationof theseactivitiesreducedtheoverallcostof individualprojectswithaminorincreasetoeitherslashpilingorsubsoilingcosts.Thesubsoilingexcavatorbucketisanotherimplementthatisalsoequippedwithshanks,andallowscost-effec-tivedecommissioningofroads.Thisimplementalsoreducesthesubsoilingrateonsmalltillageprojectsandmakesadditionalequipment(i.e.dozerandtillageimplement)redundant.

Tillage is aimedat alleviating theeffectsofdetrimental compaction,whichincludeincreasesinsoilstrength,reducedaeration,andexcessivewaterreten-tion.Althoughtheeffectivenessoftillagehasbeenquestionedonfine-texturedsoilsincentralAlbertawheresubsoilsstayedwetandsoftforlongperiodsduringtheyear(McNabb1994),suchissuesmaybelessofaconcerninfine-texturedtephra-derivedsoilsinthePacificNorthwestbecauseof(a)thestrongaggrega-tionexpectedinfine-texturedsoilsderivedfromvolcanicmaterials,and(b)dryerclimates.Forrelativelyfreshvolcanicparentmaterials,particlesizesmaybecoarseandwaterinfiltrationandaerationmaynotbelimiting.

Insummary,forsuccessfultillage,consider:

• tillageisusedtoreducesoilstrengthandrestoretheporesystem, • avarietyofimplementsareavailable, • usetherootingdepthinnaturalforestsonsimilarsitesasaguidetotillage

depth • fordisperseddisturbance,andtoreducecosts,considerspottillage • theeffectsoftillingwetvolcanicsoils,whichmaybesubjecttoirreversible

dryingorconsolidation,needtobeevaluatedthroughmonitoring

Restoring Organic Matter and Nutrients

Ingeneral, themosteffectivemeansofrestoringsurfacesoilorganicmatteristoretrieveandreplacedisplacedtopsoil.Insituationswhererecoveryofdis-placedsurfacesoilisnotpractical,otherpotentialstrategiesincludedistributinggreenloggingslashfromharvestingoperationsoverthereclaimedarea.IncentralBC,chippedwastelogsenhancedsoilpropertiesandcontributedtosuccessfulestablishmentandearlygrowthofwhitespruceseedlings(Sanbornandothers2004).Despitetheirbenefits,organicamendmentsaregenerallyonlysuitableiftheyarelocallyavailable,astheyareexpensivetotransport.



Sincetephraderivedmaterialsareknowntohaveahighaffinityforsoilor-ganicmatter,acost-effectivealternativecouldinvolverevegetationwithgrassesandlegumesthatcanbuildsoilorganicmatterthroughdecompositionoftheirrootsystems.Inonestudy(notanashsoil),Bendfeldtandothers(2001)showedthatvegetationinputsofCwereanimportantsourceofsurfacesoilorganicmat-terlevelsaftersixteenyearsonreclaimedminesoilthatalsoreceivedaninitialamendmentwithwoodwaste.

Insummary,torestoreorganicmatterandnutrients,consider:

• Organic matter is an essential component of productive soil, but forestecosystemsvaryintheamountpresentinsurfacesoils.

• Retrievalofdisplacedtopsoilisacosteffectiveapproachforrestoringsuit-ablegrowingconditions.

• Usethecharacteristicsofsurfacesoilsonsimilarsitesasaguidetowhatsurfacesoilorganicmatterlevelsareappropriate,anditsdistributionasasurfacelayerorincorporatedintosurfacesoils.

• Revegetationwithagronomicgrassesandlegumescancontributesignificantquantitiesoforganicmatterovertime.

• Organicamendmentscaneffectivelyrestoresoilconditions,butareexpen-sivetotransport.

Revegetation

Successful revegetation and reforestation of disturbed areas is an importantfinalstepinreclamationefforts.Inmanycases,theobjectiveforthereclamationisdefinedbythetypeofvegetationcoverdesired.Forexample,grassandlegumecovermaybeprescribedtopreventerosion,forestrestorationprovidesfortimber,orothervaluesmayhaveprioritysuchaswildlife,watershedvalues,andaesthetics.Treeplantingisthemostcommonandeffectivemeanstoestablishanewforest,butnaturalregenerationcouldbeeffectiveifaseedsourceandsuitableseedbedconditionswerepresent.

Forsuccessfulandcost-effectiverevegetation,consider

• Revegetationisessentialforerosioncontrolinslopingterrain.

• Seeding agronomic grasses and legumes are proven means to preventerosion.

• Seedbed characteristicsareoftenbestimmediatelyaftertillageoperationsarecomplete.

• Droughtiness;mayhamperrevegetationeffortsincoarse-texturedtephraswherelowwaterretentionresultsinalackofseedbedmoisture.Seedingtreatmentsinsuchsoilswouldhavetobeconsideredcarefully,andconsiderthetiminginrelationtoexpectedprecipitation,alongwiththepossibleneedformulchestoconservemoisture.

• Ingress of native vegetation mayoccurwithoutinterventionwheredistur-bancesaresmall(e.g.roadsandtrails).

• Natural regeneration of tree seedlingsmaybea lowcostalternative toplantingwhereaseedsourceisavailableandslightlylongerregendelayisacceptable.

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Information and Research Needs _________________________________Thepublishedinformationbaseislimitedandprovidesfewspecificexamples

oftheeffectsofsoildisturbance,enhancementandrestorationonforestsitepro-ductivityinvolcanicterraininwesternNorthAmerica.Thelackofinformationpartlyreflectsthedifficultyandexpenseindesigningandimplementingstudiesthatarerelevanttothewiderangeofsitetypes,soilconditions,andtreespeciesthatoccurintheregion.Despitethis,thereisconsiderableinformationonsoildisturbanceandrestorationeffectsforothersoiltypesinsimilarclimatesandmuchofthisinformationcanlikelybeextrapolatedtovolcanicsoilsintheNorthwest.Inaddition,soilscientistsandforestmanagersintheregionhaveconsiderableexperiencewithhowthesoilsrespondtomanagement.

Toaddressthelackofspecificpublishedinformation,ausefulapproachwouldbetocombineexistingresearchfromelsewherewithlocalknowledgeofthesoilsresponsetomanagementthroughretrospectivestudy,monitoring,andoperationaltrials.Althoughtheseapproacheshavetheirlimitationsforresolvingdetailedques-tions,theyareextremelyusefulforansweringthebroadquestionsthatariseduringtheinitialstagesofadetailedresearchprogram.Specificquestionstobeaddressed(andsuggestedapproachtostudy)include:

• Identifyingsitesmostsusceptibletodegradation,andthosewhererestorationorenhancementprovidethegreatestbenefit(monitoring and retrospective study)

• Evaluatingarangeoftreatmentoptionsforrestoringandenhancingproduc-tivity(monitoring results and operational trials)

• Characterizing theeffectof typicaloperationsonsoilpropertiessuchasbulkdensity,penetrationresistance,andorganicmatter(research)

• Determiningthresholdsforunacceptableproductivitydeclineonthemostcommonsitetypes(research)

Management Recommendations _________________________________1. Evaluate costs and benefits:Soilrestorationandenhancementshouldbe

consideredinvestmentswheretheexpectedbenefits,costsandrisksarecarefullyevaluated.Ingeneral,itisbesttofocuseffortsonsiteswiththebestexpectedreturnonrestorationdollars,anduselowcost,reliablemethodsforrestoration.Thebenefitsofrestorationandenhancementeffortstypicallyinclude:

• increasedtimbersupply, • reducedenvironmentalliabilityassociatedwithroads, • improvedwatershed,wildlife,andaestheticvalues.

2. Have a site-specific plan:Evaluatelimitationstoproductivity,riskofero-sion,andothersitespecificfactors,andthensetrealisticobjectivesforthework.Wherelegacyimpactsarepresent,combinationmachinessuchasthesubsoilinggrapplerakeandsubsoilingexcavatorbucketmayallowrestorationtobeblendedintootherworksuchasbrushpilingorroaddecommissioning.

3. Start simple (and cheap):Trythesimplesolutionfirst.Considertreatmentsinthefollowingorder:

• donothing(i.e.relyonnaturalregenerationtorecolonizelightlydisturbedareas)



• treeplanting • fertilization • decompaction/tillageplustopsoilrecovery • organicamendments • re-establishingnativespeciesbyplanting

4. Keep learning:Monitortheresultsofyoureffortsandthoseofothers.

Acknowledgments ______________________________________________ResearchdescribedherewassupportedbyBritishColumbia’sForestScience

Programandother fundingsources.UmpquaNationalForest supportedworkof J.Archuleta.MikeKarrprovidedworkon the subsoilingequipmenton theUmpquaNationalForest.

References ______________________________________________________Amaranthus,M.P.;Page-Dumroese,D.;Harvey,A.;Cazares,E.;Bednar,L.F.1996.Soilcompac-

tionandorganicmatteraffectconiferseedlingnonmycorrhizalandectomycorrhizalroottipabundanceanddiversity.PNW-RP-494.Portland,OR:U.S.DepartmentofAgriculture,ForestService,PacificNorthWestStation.12p.

Archuleta,J.G.;Karr,M.2004.Multipurposesubsoilingexcavatorattachments.Tech.Tip.SanDimastechnologydevelopmentCenter.U.S.DepartmentofAgriculture,Forestservice.

Arnalds,O.;Kimble,J.2001.AndisolsofdesertsinIceland.SoilSci.Soc.Am.J.65:1778-1786.Basher,L.R.;Painter,D.J.1997.WinderosioninNewZealand.In:ProceedingsoftheInterna-

tionalSymposiumonWindErosion;1997June3-5;Manhattan,Kansas:U.S.DepartmentofAgriculture,ARS:1-10.

Bendfeldt,E.A.;Burger,J.A.;Daniels,W.L.2001.Qualityofamendedminesoilaftersixteenyears.SoilSci.Soc.Am.J.65:1736-1744.

BritishColumbiaMinistryofForests.2001.Soilconservationguidebook.BCMin.For.Victoria.Available: http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/soil/soil-toc.htm. AccessedOctober2005.

Bulmer,C.E.;Krzic,M.2003.SoilpropertiesandlodgepolepinegrowthonrehabilitatedlandingsinnortheasternBritishColumbia.Can.J.SoilSci.83:465-474.

Bulmer,C.E.;Staffeldt,P.2004.SalmonArmlandingrehabilitationmonitoringreport.Unpublishedtechnicalreportavailablefromtheauthor.

Cairns,J.Jr.1999.Ecologicalrestoration:Amajorcomponentofsustainableuseoftheplanet.RenewableResourcesJournal:7-11.

CanadianCouncil of ForestMinisters. 2002.Technicalworkinggroupdraft recommendationsforimprovedCCFMindicatorsforsustainableforestmanagementdraftcompiledbytheC&IsecretariatOctober2,2002.TWGChairsmeeting;2002October9–11;Edmonton,Alberta.CCCFMSecretariat8thFloor,580BoothStreetOttawa.

Hillel,D.1991.Outoftheearth.Berkeley,CA:UniversityofCaliforniaPress.322p.McNabb,D.H.1994.TillageofcompactedhaulroadsandlandingsintheborealforestsofAlberta,

Canada.For.Ecol.Mgmt.66:179-194.Miller,R.E.;Scott,W.;Hazard,J.W.1996.Soilcompactionandconifergrowthaftertractoryard-

ingatthreecoastalWashingtonlocations.Can.J.ForRes.26:225-236.Moldrup,P.;Yoshikawa,S.;Olesen,T.;Komatsu,T.;Rolston,D.E.2003.GasDiffusivityinUn-

disturbedVolcanicAshSoils:TestofSoil-Water-Characteristic-BasedPredictionModels.SoilSci.Soc.Am.J.67:41–51.

Page-Dumrose,D.;Jurgensen,M.;Elliot,W.;Rice,T.;Nesser,J.;Collins,T.;Meurisse,R.2000.SoilqualitystandardsandguidelinesforforestsustainabilityinnorthwesternNorthAmerica.For.Ecol.Manage.138:445-462.

Plotnikoff,M.R.;Bulmer,C.E.;Schmidt,M.G.2002.Soilpropertiesandtreegrowthonreha-bilitatedforestlandingsintheinteriorcedarhemlockbiogeoclimaticzone:BritishColumbia.For.Ecol.Mgmt.170:199-215.



Poulenard,J.;Podwojewski,P.;Herbillona,A.2003.Characteristicsofnon-allophanicAndisolswithhydricpropertiesfromtheEcuadorianparamos.Geoderma.117:267–281.

Poulenard,J.;Michel,J.C.;Bartoli,F.;Portal,J.M.2004.WaterrepellencyofvolcanicashsoilsfromEcuadorianparamos:effectofwatercontentandcharacteristicsofhydrophobicorganicmatter.EuropeanJournalofSoilScience.55:487–496.

Powers,R.F.;Tiarks,A.E.;Boyle, J.R.1998.Assessingsoilquality:Practicablestandards forsustainableforestproductivityintheUnitedStates.In:Thecontributionofsoilsciencetothedevelopmentofandimplementationofcriteriaandindicatorsofsustainableforestmanagement.Soil.Sci.Soc.Am.Spec.Pub.no.53.Madison,WI:SoilScienceSocietyofAmerica:53-79.

Richardson,B.;Skinner,M.F.;West,G.1999.Theroleofforestproductivityindefiningthesus-tainabilityofplantationforestsinnewZealand.For.Ecol.Manage.122:125-137.

Sahaphol,T.;Miura,S.2005.Shearmoduliofvolcanicsoils.SoilDyn.Earth.Eng.25:157-165.Sanborn,P.;Bulmer,C.;Coopersmith,D.2004.Useofwoodwasteinrehabilitationoflandings

constructedon fine-textured soils, central interiorBritishColumbia,Canada.West. J.Appl.For.19:175–183.

Shoji,S.;Nanzyo,M.;Dahlgren,R.A.;Quantin,P.1996.EvaluationandproposedrevisionsofcriteriaforAndosolsintheworldreferencebaseforsoilresources.SoilSci.161:604-615.

Tejedor,M.; Jimenez,C.C.;Dıaz,F.2002.SoilMoistureRegimeChangesinTephra-MulchedSoils:ImplicationsforSoilTaxonomy.SoilSci.Soc.Am.J.66:202–206.

Tejedor,M.;Jimenez,C.C.;Dıaz,F.2003.Volcanicmaterialsasmulchesforwaterconservation.Geoderma.117:283–295.



Mariann T. Garrison-Johnston and Peter G. Mika are research scientists and Leonard R. Johnson is the director for the Intermountain Forest Tree Nutrition Cooperative, University of Idaho, Moscow, ID. Dan L. Miller is a silviculture manager for Potlatch Corporation, Lewiston, ID. Phil Cannon is the productivity manager for Forest Capital, North, Monmouth, OR.

Abstract Datafrom139researchsitesthroughouttheInlandNorthwestwereanalyzedforeffectsofashcaponsiteproductivity,nutrientavailabilityandfertilizationresponse.Standproductivityandnitrogen(N)fertilizerresponseweregreateronsiteswithashcapthanonsiteswithout.Whereashwaspresent,depthofashhadnoeffectonsiteproductivityorNfertilizerresponse.Siteproductivityincreasedwithincreasingpotentiallyavailablesoilwater.Potentiallyavailablesoilwater,inturn,increasedwithincreasingashdepth.Decreasingavailabilityofmagnesium(Mg)andcalcium(Ca)intheupper12inchesofsoilmayhaveconstrainedsiteproductivitywithincreasingashdepth.SoilmineralizableNandammoniumNwereunaffectedbyashpresenceordepthbutdidvarybyunderlyingparentmaterial.SiteproductivityandNfertilizerresponsevariedbyunderlyingparentmaterialevenafteraccountingforashpresence.Standvolumeresponsetosulfur(S)fertilizationdecreasedwithincreasingashdepth,suggestingpossibleSadsorptionbyashcap.NogrowthresponseorchangeinfoliarKstatuswasdiscernedfollowingKfertilization.Managementrecommendationsbyparentmaterialareprovided.

Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland

NorthwestMariann T. Garrison-Johnston, Peter G. Mika, Dan L. Miller, Phil Cannon, and

Leonard R. Johnson

Background

Availabilitytoplantsofmostnutrientsbesidesnitrogen(N)isrelatedprimarilytomineralweatheringratesandsoilphysicalandchemicalproperties.CommonparentmaterialsofsoilsintheInlandNorthwestincludetheColumbiaRiverbasaltflows,BeltSeriesmetasedimentaryrocks,granites,andvariousglacialdeposits.Characteristicsthatthesematerialsimparttofor-estsoilssignificantlyaffectforestnutrition,productivityandresponsetofertilization(MooreandMika1997;Mooreandothers2004).However,surficiallydepositedparentmaterialsareoftenneglectedduringanalysesofparentrockeffectsonforestnutrition.ThisisparticularlytrueforwidespreadvolcanicashresultingfromtheeruptionofMountMazama(nowCraterLake)insouthwesternOregon.Theeffectsofsurficiallydepositedparentmaterialsonforestnutrition,productivityandresponsetofertilizationarepoorlyunderstood.

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Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

Ash-capsoilscommontotheInlandNorthwestareknownfortheircapabilitytoholdampleavailablemoisture,whichinturnisthoughttoenhancesitepro-ductivity (BrownandLowenstein1978;Mital1995).Becauseof theimprovedsoilmoisturestatus,foreststandsgrowingonash-capsoilsaregenerallyexpectedto show greater growth response to nitrogen (N) fertilization than stands onsoilswithoutashcap,atleastsolongassomeotherfactorisnotmorelimitingthan moisture and/or N. In a study of 90 Douglas-fir fertilization trial standsacrosstheInlandNorthwest,Mital(1995)foundapositivecorrelationbetweenDouglas-firgrowthresponsetoNfertilizationandashdepthatanapplicationrateof400lbac–1,whiletherelationshipwaslessstrongwhentheapplicationratewas200lbac–1.Inanotherstudy,Geist(1976)reportedthatforageproductiononvolcanicashsoilsshowedstrongfertilizationresponseonforestedrangesitesineasternOregonandWashington.

Withoutfertilizersorblendingwithorganicmatter,unweatheredash-capsoilsarenotparticularlyfertile,beingcomprisedlargelyofpoorlycrystallinealumi-nosilicatesandiron(Fe)andaluminum(Al)oxides.Theirnutrientcationstoragecapacity is low, suggesting that supply of the nutrient cations potassium (K),calcium(Ca)andmagnesium(Mg)maybepoor(McDanielandothers2005).Furthermore,stronganionadsorptioncapacitybyvolcanicashmayimpedetreefertilizationresponse.Inastudyofsulfur(S)adsorptionpropertiesofandicsoilsintheInlandNorthwest,Kimseyandothers(2005)suggestthatappliedSfertilizersmaybeineffectiveinincreasingS-availabilitytotreesunlessathresholdsorptioncapacityof theashcapisexceeded.Similar interactionsmaybeexpectedfortheanionicformsofotherelements,includingN,phosphorus(P)andboron(B).Suchaphenomenonmayexplain,inpart,thevariablerelationshipbetweenashcapdepthandN-fertilizationratesdescribedbyMital(1995),ifsomethresholdsorptioncapacityhadtobemet(suchasatthe400lbrate)beforetheappliedNbecameavailabletotheforestvegetation.Theashcapmaytakeonnutritionalcharacteristicsofunderlyingresidualsoils,thoughthisperceptionhasnotbeenscientificallytested.

AstatisticalanalysisofdatafromnutritionalresearchconductedbytheInter-mountainForestTreeNutritionCooperative(IFTNC)from1980tothepresentwasundertakentodeterminewhetherashdepositsaffectedtreeandsoilnutrition,for-estproductivityandfertilizationresponse.Wehypothesizedthatsiteproductivityandfertilizerresponsewouldbegreateronashsitesthannon-ashsitesandthatproductivityandresponsewouldincreasewithincreasingashdepth.

Methodology ___________________________________________________

Data Compilation

Data from139 IFTNC research siteswere compiled.Thedata set included94sitesfromthe1980-1982Douglas-firStudy,8siteseachfromthe1991and1993MixedConiferStudies,and29sitesfromthe1994-1996ForestHealthandNutritionStudy(table1).Soilprofiledescriptionswereusedtoestimateorganichorizondepth,surficialdepositdepthandresidualsoildepthto36inches.Sur-ficial deposits were categorized as ash, loess, glacial deposits, other modern(quarternaryera)deposits,andtertiarydeposits.Residualsoilswerethosederivedfromthebasegeology.Thedivisionbetweensurficialdepositsandbasegeology


Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest Garrison-Johnston, Mika, Miller, Cannon, and Johnson

Tabl

e 1—

List

of

sele

cted

fer

tiliz

atio

n st

udie

s es

tabl

ishe

d by

the

Int

erm

ount

ain

Fore

st T

ree

Nut

ritio

n C

oope

rativ

e be

twee

n 19

�0 a

nd 2

000.

R

egio

ns r

efer

to

nort

heas

tern

Ore

gon

(NE

OR

), ce

ntra

l Was

hing

ton

(C W

A), n

orth

east

ern

Was

hing

ton

(NE

WA)

, cen

tral I

daho

(C ID

), no

rthe

rn Id

aho

(N ID

) and

wes

tern

M

onta

na (W

MT)

.

No.

of

Year

(s)

Stan

d

Tria

l nam

e si

tes

esta

blis

hed

com

posi

tion

Reg

ion

Trea

tmen

ts a

nd r

ates

a

Dou

glas

-fir

trial

s 94

19

�0-1

9�2

Dou

glas

-fir

C ID

, C W

A,

cont

rol;

200

lb N

; 400

lb N

N

E W

A, N

E O

R,

N ID

, W M

T

Um

atill

a m

ixed

con

ifer

� 19

91

Mix

ed c

onife

r N

E O

R

cont

rol;

200

lb N

; 200

lb N

+ 1

00 lb

S

Oka

noga

n m

ixed

con

ifer

� 19

9�

Mix

ed c

onife

r C

WA

co

ntro

l; 20

0 lb

N; 2

00 lb

N +

170

lb K

Fore

st h

ealth

and

29

19

94-1

99�

Mix

ed c

onife

r C

ID, C

WA

, NE

19

94 (1

2 si

tes)

: c

ontro

l; �0

0 lb

N; 1

70 lb

K; �

00 lb

N +

170

lb K

nutri

tion

W

A, N

E O

R, N

ID

199�

(12

site

s):

con

trol;

�00

lb N

; 170

lb K

; �00

lb N

+ 1

70 lb

K;

�00

lb N

+ 1

70 lb

K +

100

lb S

19

9� (7

site

s):

con

trol;

�00

lb N

; 170

lb K

; �00

lb N

+ 1

70 lb

K;

�00

lb N

+ 1

70 lb

K +

100

lb S

+ �

lb B

+ 1

0 lb

Cu

+10

lb Z

n +

0.1

lb M

o

All

year

s: A

dditi

onal

N+K

com

bina

tions

rang

ing

from

0 lb

N a

nd

0 lb

K to

�00

lb N

and

�12

lb K

, per

exp

erim

enta

l des

ign

a R

ates

in lb

ac–

1 as

bro

adca

st a

pplic

atio

n



wasnotalwaysclear.Becausethesoildepthparameterforthisstudywaslimitedto36inches,deepsurficialdepositswereoftentheonlyparentmaterialnoted.Therefore,thebasegeologicparentmaterialcategoriesforthispaperincludedbasalt,granite,sedimentaryrock,metasedimentaryrock,glacialdeposit,tertiarysedimentsandmodernsediments.Ashwasconsideredpresentifitwascontinu-ousandmeasurabletoadepthof1inchorgreater.Admixturesofashandothermaterialswerealsocountedasashcapiftheashwasapredominantandidentifi-ablecomponentofthemix.

Soilwater-holdingcapacitywasdetermined for theupper24 inchesof thesoil profile on 110 sites. Potential plant-available water was calculated as thedifferenceinmoisture-holdingcapacitybetween1/3and15barsforthosesites.Conventionallaboratorysoiltestswereperformedontheupper12inchesofsoilforall139sites,thoughsometestswereperformedononlyasubsetofthesites.AvailablePandKweretestedusingsodiumacetateextraction,whileNH4

+andNO3

–wereanalyzedusing2MKClextractionwithanalysisbycolorimetry(CaseandThyssen1996a;CaseandThyssen1996d).Sulfate-sulfurwasanalyzedbycalciumphosphateextractionandionchromatography,andBwasanalyzedbycalciumchlorideextractionandspectrophotometricdetermination(Case1996;CaseandThyssen1996c).ExtractableCa,Mg,KandNawereanalyzedby1NammoniumacetateextractionandICP,andmicronutrientsCu,Zn,MnandFebyDTPA(CaseandThyssen1996b;CaseandThyssen2000).

Twodifferentapproacheswereusedtoestimatesiteproductivity.Thefirstap-proachutilizedDouglas-firsiteindex(SI,Monserud1984),availablefor110ofthe139sites.Wealsoselectedcontrolplotgrowthrate(CGR)asaneasilycal-culatedproductivityestimateavailableforallsitesincludedinthestudy.Controlplotgrowthratewasestimatedastheaveragegrowthrateinft3ac–1yr–1overthefirst6yearsofeachstudy.Fertilizationresponsewasbasedon6-yearcubicfootvolumeresponse(ft3ac–1yr–1)toNfertilizersappliedat200to300lbNac–1.LimiteddatawereavailableforexaminationofvolumeresponsetoSfertilizersappliedat100lbSac–1andKfertilizersappliedat170lbKac–1.

Treenutritionwasassessedbychemicalanalysisoffoliagecollectedoneyearafterfertilizationfromtheupperthirdofthecrownondominantorco-dominanttrees.Becausefoliagechemistrydiffersfordifferenttreespecies,Douglas-firwasselectedforinclusioninthisanalysisasthespeciesmostcommonlyoccurringacrosstheselectedtestsites.Nutrientdeficiencieswereidentifiedbythecriticallevelsmethod,definedasthepointonayieldcurvewhereanincreaseinnutri-entconcentrationnolongerresultsinincreasedyield.Thus,the“criticallevel”istheoptimumnutrientconcentrationatwhichmaximumyieldisobtainedwithminimumnutrientinput.CurrentlyacceptedcriticallevelsforInlandNorthwestDouglas-firfoliageareshownintable2.

Data Analysis

Sites were arrayed in a matrix by geographic region, rock type, vegetationseriesandashcappresenceorabsencetoevaluatesamplesizesineachcategory.Analysisofvariancewasusedtodetecttheeffectsofregion,rocktype,vegetationseriesandashpresenceonsiteproductivity,soilandfoliagecharacteristicsandfertilizationresponse.Thebasicstatisticalmodelusedforthisanalysiswas:

Yijk=µ+αj+βk+(αβ)jk+εijk (1)



Table 2—Nutritional critical levels for Douglas-fir foliage. Adapted from Webster and Dobkowski (19��).

Nutrient Unit of concentration Critical levelNitrogen (N) % 1.40Phosphorus (P) % 0.12Potassium (K) % 0.�0Sulfur (S) % 0.11Calcium (Ca) % 0.1�Magnesium (Mg) % 0.0�Manganese (Mn) ppm 1�Iron (Fe) ppm 2�Zinc (Zn) ppm 10Copper (Cu) ppm 2Boron (B) ppm 10

Where:

Yijk=theproductivity,soilorfoliagecharacteristicmeasuredateachsiteµ=populationgrandmeanforproductivity,soilorfoliagecharacteristicαj=effectofregion,parentmaterialorvegetationseriesβk=effectofashpresenceorabsence(dummyvariable)(αβ)jk=effectofregion,parentmaterialorvegetationseriesbyashcapinteractionεijk=theerrorterm~NID(0, σ2)

BecauseCGRwasafunctionofinitialvolume,analysesofCGRincludedinitialvolumeasacovariateintheabovemodel.Similarly,becausefertilizationresponsedependedonstartingvolumeandstandgrowthrate,thosevariableswereusedascovariatesforthatanalysis.Ashdepthasacontinuousvariablewasalsoincor-poratedintotheabovemodeltoperformregressionanalysisoftheeffectsofashdepthonallvariablesexaminedinthisstudy.Resultswereconsideredsignificantatthe90%confidencelevel(p=0.10).

Results _________________________________________________________

Ash Distribution

SitesinnorthIdaho,northeastWashingtonandnortheastOregonweremorelikelytohaveashthansitesincentralWashington,MontanaandcentralIdaho(table3).Sitesontertiarydeposits,metasedimentaryrocksandglacialdepositsweremorelikelytohaveashthanthoseonbasalt,granite,modernsedimentarydepositsandsedimentaryrocks.Almostallwesternredcedarandwesternhemlockvegetationseriesoccurredonsiteswithash,whileonlyabouthalfthegrandfirseriesandaquarteroftheDouglas-firseriesoccurredonsiteswithashcap.Thestatisticaltermforthispatternwherebyashoccursinconjunctionwithcertaincharacteristicsandnotothersisknownas“confounding.”Confoundingbetweenashpresenceandothersitecharacteristicsmakestatisticalanalysisdifficultbecausewecannotdeter-minewhetherproductivityorresponsedifferencesbetweensitesareduetotheashpresence/absenceortheothersitecharacteristic(vegetationseries,parentrockorgeographicregion).Theoccurrenceofashinconjunctionwithcertainparentrocks



orgeographicregionsislikelycoincidental,whiletheoccurrenceofashinconjunc-tionwithcertainvegetationseriesismoresuggestiveofacausalrelationship.

Site Productivity

Douglas-firSIwasanalyzedfor110sites(SIinformationwasnotavailablefortheForestHealthandNutritionStudysites).Overall,SIwas10.6%greateronsiteswithashcapthansiteswithout.BaseparentmaterialexplainedasignificantamountofSIvariation(R2=0.18),andtheadditionofashpresencetothismodelexplainedsomeadditionalvariationinSI(R2=0.28;fig.1a).Onallparentmaterialtypesexceptbasalt,thepresenceofashcapsomewhatincreasedsiteproductivitycomparedtothenon-ashsites.However,givenashpresence,asubsequentregres-sionanalysisrevealednosignificantinfluenceofashdepthonSI(fig.1b).AverageSIdidvarybygeographicregion(fig.1c);however,ashpresenceorabsencedidnotfurtherexplainvariationinSIoncethegeographicregionwasknown.Similarly,whileasignificantamountofvariationinSIwasexplainedbyvegetationseriesalone(fig.1d),ashpresencedidnotexplainanyfurthervariation.

Controlplotgrowthratewasavailableforall139sitesincludedintheanalysis,andwashighlycorrelatedwithSI(R2=0.59).Overall,CGRwas29.0%greateronashversusnon-ashsites.AshdepthdidnotaffectCGR(fig.2a).Controlplotgrowthratewassignificantlyaffectedbygeographicregion(R2=0.58;fig.2b),

Table 3—Number of research sites with and without ash cap by region, underlying geology and vegetation series.

Ash cap present? Percent sites Region no yes Total with ash cap

North Idaho � 2� �1 �4%Northeast Washington � 17 2� 74%Northeast Oregon 7 10 17 �9%Central Washington 2� 11 �4 �2%Montana 14 2 1� 1�%Central Idaho 17 1 1� �% Underlying geology

Tertiary deposits 1 � 7 ��%Metasedimentary rocks � 20 2� 71%Glacial deposits � 17 2� ��%Basalt 2� 1� �� 4%Granite 1� 9 27 ��%Modern deposits 7 2 9 22%Sedimentary rocks � 0 � 0%

Vegetation series

Western red cedar 1 22 2� 9�%Western hemlock 1 � � ��%Grand fir 29 24 �� 4�%Subalpine fir � 2 � 40%Douglas-fir �� 14 �2 27% Total sites with and without ash cap: 72 67 139 48%



Figure 1a—Douglas-fir site index by base parent material and ash cap presence. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 1b—Douglas-fir site index (ft at �0 years) by ash cap depth for sites with ash cap.

Figure 1d—Douglas-fir site index by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF), subalpine fir (SAF), western hemlock (WH) and western red cedar (WRC).

Figure 1c—Douglas-fir site index by geographic region. Regions include central Idaho (C ID), central Washington (C WA), Montana (MT), north Idaho (N ID), northeast Oregon (NE OR) and northeast Washington (NE WA).



vegetation series (R2=0.59; fig. 2c) and dominant parent material (R2=0.46;fig.2d).Ashpresencedidnotexplainanyadditionalvariationforthegeographicregionorthevegetationseriesmodels.However,ashpresencedidexplainsomeadditionalvariationinCGRintheparentmaterialmodel(R2=0.57;fig.2e).TheresultsweresimilartothoseforSI,withashpresencesomewhatincreasingCGRformostparentmaterials.AlsosimilartoSI,onceashwaspresentCGRdidnotchangewithashdepth.

Site Fertility

Soil moisture—Siteproductivityincreasedwithincreasingpotentiallyavailablewater(fig.3a).Potentiallyavailablewater,inturn,increasedwithincreasingashdepth.Whenarrayedbyvegetationseries,potentiallyavailablewaterwasgreater

Figure 2a—Control plot growth rate by ash cap depth for sites with ash cap.

Figure 2b—Control plot growth rate (ft�ac –1yr –1) by geographic region. Regions include central Idaho (C ID), central Washington (C WA),Montana (MT), north Idaho (N ID), northeast Oregon (NE OR) and northeast Washington (NE WA).



Figure 2e—Control plot growth rate ft�ac –1yr –1) by base parent material and ash cap presence. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), mod-ern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 2c—Control plot growth rate (ft�ac –1yr –1) by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF), subalpine fir (SAF), western hemlock (WH) and western red cedar (WRC).

Figure 2d—Control plot growth rate ft�ac –1yr –1) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



onsitesonwesternredcedarseriescomparedtositesonDouglas-firandgrandfirseries(fig.3b).Whenarrayedbyparentmaterial(fig.3c),siteswithashcapsonbasaltandmetasedimentaryparentmaterialsaveragedhigherpotentialwateravailabilitythanthoseongraniteandglacialtillparentmaterials.However,whenashwasabsent,sitesonglacialtillparentmaterialshadhigherpotentiallyavail-ablewaterthansitesonmetasedimentaryorgraniticrocks.

Soil Acidity—SoilpHdatawereavailablefor135sites.Overall,pHincreasedwithincreasingashdepth.VegetationserieshadasignificanteffectonpH,withsitesonsubalpinefirserieslessacidthanthoseongrandfirorDouglas-firseries,whichinturnwerelessacidthansitesonwesternredcedarorwesternhemlockseries (fig. 4a). Parent material also affected soil pH, but interacted with ash

Figure 3a—Control plot growth rate ft�ac –1yr –1) and Douglas-fir site index (ft at �0 years) as a function of potential available water (inches) in the upper 24 inches of soil.

Figure 3c—Potentially available water (inches) in the upper 24 inches of soil as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite and metasedimentary (metased).

Figure 3b—Potential available water (inches) in the upper 24 inches of soil as a function of ash depth (inches), by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF) and western red cedar (WRC).



depth(fig.4b).Soilaciditydecreasedwithincreasingashdepthongraniteandperhapsbasaltparentmaterials,andincreasedwithincreasingashdepthonter-tiarysediments,butshowedlittlevariationwithashdepthonotherunderlyingparentmaterials.Intheabsenceofash,soilaciditywasaboutthesameforallunderlyingparentmaterials.

Nitrogen—Soil mineralizable N data were available for 119 sites, whileammonium-Ndatawereavailable for45sitesandnitrate-Ndata for44sites.Noneof these threemeasuresofsoil-availableNvariedwithashpresenceordepth.However,twoofthevariables,soilmineralizableNandammonium-N,variedbyparentmaterial(fig.5aand5b).Bothmeasuresshowedhighervaluesonmetasedimentaryandtertiarydepositparentmaterials,andlowervalueson

Figure 4a—Soil pH by vegetation series. Vegetation series include Douglas-fir (DF), grand fir (GF), subalpine fir (SAF), western hemlock (WH) and western red cedar (WRC).

Figure 4b—Soil pH as a function of ash depth (inches) and base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



graniticandbasalticmaterials.InanefforttodeterminewhyparentmaterialwouldaffectsoilmineralizableN,severaladditionalstatisticalanalyseswereperformedusingdataonpercentorganicmatter(29sites)andpercentcarbon(90sites).Min-eralizableNwasstronglyandpositivelycorrelatedwithbothsoilorganicmatter(R2=0.69)andsoilcarbon(R2=0.68),suggestingthatparentmaterialcouldaffectsoilmineralizableNbyaffectingsoilorganicmatterand/orcarboncontent.

FoliarNconcentrationsofunfertilizedDouglas-firtreeswerebelowthecriticallevelof1.4%formostsites,andweregenerallyunaffectedbyashpresenceordepth.However,foliarNwasaffectedbyunderlyingparentmaterial,withtreesonbasaltparentmaterialsshowinghigherfoliarNconcentrationsthantreesonotherparentmaterialtypes(fig.5c).ExaminationofSIasafunctionoffoliarNshowedapositiverelationship(R2=0.28;fig.5d).Theslopeoftherelationshipdidnotvarybyunderlyingparentmaterial,butSIwashigherontertiarysedimentsandmetasedimentaryrocks.FoliageNconcentrationswerealsoanalyzedasafunctionofsoil-available(mineralizable)N,withtheexpectationthatfoliageNlevelswouldincreasewithincreasingsoilmineralizableNlevels.However,thecorrelationwasveryweak(R2=0.05).Amodelcombiningtheeffectsofrocktype,mineralizableNandelevationbetterdescribedvariationinfoliageN(R2=0.27),withfoliageNpositivelyrelatedtomineralizableNandnegativelyrelatedtoel-evation.Interestingly,thismodelshowedthattreesonbasalt,sedimentaryrockormodernsedimentshadhigherfoliarNconcentrationsthanthoseonglacialtillsormetasedimentaryrocks.Othersitefactorsincludingsoilfertility,soilwaterpotential,aspectandslopewerenotrelatedtofoliageN,andfoliageNdidnotvarybyvegetationtypeorgeographicregion.ThissuggestedthatunderlyingrockdidsomehowinfluencefoliageNnutrition.

Cations—Extractablecationdatafromsoilsamplesfrom119sitesindicatedthatextractableKwasnotaffectedbyashcappresenceordepth,butwasaffectedbyunderlyingparentmaterial(fig.6a).ExtractableCaandMgbothdecreasedwithincreasingashdepth(Ca:R2=0.30,fig.6bandMg:R2=0.33,fig.6c).Giventhesamedepthofash,CaandMgwerelowestonsiteswithgraniticparentmateri-alsandhighestonbasaltandmetasedimentaryparentmaterials.Incontrastto

Figure 5a—Soil mineralizable nitrogen (N, ppm) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



Figure 5b—Soil ammonium-nitrogen (NH4-N, ppm) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 5d—Site index (ft�ac –1yr –1) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 5c—Douglas-fir foliar nitrogen (N) con-centration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



soilK,Douglas-fir foliarKwasunaffectedbyunderlyingparentrock,butwasconsistentlyhigherinthepresenceofash(fig.6d).Onceashwaspresent,ashdepthhadnoeffectonfoliarK.Douglas-firfoliarCa(fig.6d)andMg(fig.6e)concentrationsbehavedsimilarlytosoilavailabilityinthatbothdecreasedwithincreasingashdepth.UnderlyingparentmaterialdidnotaffectfoliarCaorMgvalues.FoliarK,CaandMgconcentrationsweregenerallyabovenutritionalcriti-callevels(table2).

Phosphorus—Soil-availablePdatawereavailableforonly45sites.Soil-availablePwasnotaffectedbyashpresenceordepth,butwasaffectedbyparentmaterial(fig.7a),withglacialdepositsshowingthehighestPavailabilityandmetasedi-mentaryrocksthelowest.Douglas-firfoliarPvaluesweregenerallyabovecriti-callevels(table2),andwerealsounaffectedbyashpresenceordepth.FoliarPconcentrationsdifferedbyparentmaterial,andwerehighestonglacialdeposits

Figure 6a—Extractable potassium (K, cmol kg–1) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 6b—Extractable calcium (Ca, cmol kg–1) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 6c—Extractable magnesium (Mg, cmol kg–1) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial de-posit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



Figure 6f—Douglas-fir foliar magnesium (Mg) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 6d—Douglas-fir foliar potassium (K) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 6e—Douglas-fir foliar calcium (Ca) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materi-als include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



andlowestonmetasedimentaryrocks(fig.7b).NeitherfoliarPconcentrationsnorsoilPtestssuggestedanyeffectofashonPavailabilityduringthisstudy.

Sulfur, B and Cu—SufficientdatawereavailabletoperformstatisticalanalysesforavailableBandS(45sites)andCu(29sites).Givenashpresence,availableBincreasedwithincreasingashdepth(fig.8a).Therewasnoevidencethatpar-entmaterialorvegetationseriesaffectedsoilBavailability.Incontrast,availableCuwasnotaffectedbyashpresenceordepth,butdidvarybyparentmaterial,ranging from0.46ppmongranitic sites to1.03ppmonmodernsedimentary

Figure 7a—Available phosphorus (P, ppm) by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 7b—Douglas-fir foliar phosphorus (P) concentration (percent) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedi-mentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



deposits(fig.8b).Sulfate-Savailabilitywasnotaffectedbyash,parentmaterialorvegetationseries.

Douglas-firfoliarBvaluesincreasedwithincreasingashdepth,showinggoodagreementwithsoil-availableBtests(fig.8c).FoliarBwasalsoaffectedbypar-entmaterial,rangingfromabout23ppmongraniticrockstoabout29ppmontertiarysedimentsintheabsenceofash.FoliarCuvalues,incontrast,werenotaffectedbyparentmaterialorashpresenceordepth.FoliarBandCuvaluesweregenerallyabovenutritionalcriticallevels(table2).WhilefoliarSconcentrationswereatorabovecriticallevelmostofthetime,Swasthenextmostlikelyele-ment,afterN,toshowdeficiencylevels.

Figure 8a—Soil available boron (B, ppm) as a function of ash depth (inches).

Figure 8b—Available copper (Cu, ppm) by base parent mate-rial. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), mod-ern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 8c—Douglas-fir foliar boron (B) concentration (ppm) as a function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), gran-ite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



Fertilization Response

Nitrogen Fertilizer Response—Acrossallgeographicregions,baseparentma-terialsandvegetationseries,6-yeargrossvolumeresponsetoNfertilizerofstandsonash-capsiteswas49.6%greateronaveragethanfertilizerresponseofstandsonnon-ashsites.However,onceashwaspresent,ashdepthhadnoeffect.Thecombinedeffectofparentmaterialandashpresencemoreeffectivelydescribedvariationinresponsethanashcapalone.Ashpresenceincreasedvolumeresponseby87%onglacialdeposits,76%ontertiarysediments,48%onmodernsedimentsand34%onbasalts(fig.9a).Ashpresencedidnotaffectvolumeresponseonmetasedimentaryorgraniticparentmaterials.Vegetationseriesdidnotdescribeanyadditionalfertilizationresponseonceashpresencewasaccountedfor.Amodelcombiningparentmaterialandvegetationserieswasmoreeffectiveatexplain-ingvariationinresponse(fig.9b)thantheparentmaterialandashmodel.SitesonwesternredcedarvegetationseriesandbasaltorglacialtillparentmaterialsshowedthehighestNfertilizerresponse,whilesitesonDouglas-firvegetationseriesandmetasedimentaryparentmaterialsshowedthelowestresponse,withothersitesfallinginbetween.Eventhoughthisrelationshipbetweenresponseandvegetationseriessuggestedthatsoilmoisturemayaffectresponse,therelationshipbetweenvolumeresponsetoNfertilizationandpotentiallyavailablewaterintheupper24inchesofsoilwasstatisticallynonsignificant.

VolumeresponsetoNfertilizerdecreasedwithincreasingsoilmineralizableN(R2=0.34;fig.9c)andammonium-N.However,volumeresponsetoNfertilizershowednorelationshiptounfertilizedfoliarNlevels.ChangesinfoliarNcon-centrationcausedbyNfertilizationwereinverselyrelatedtounfertilizedfoliarNconcentrations(fig.9d).Inotherwords,thelowertheuntreatedfoliarNlevels,thegreaterthechangeinfoliarNresultingfromNfertilization.Neitherashpresencenordepthinfluencedthischange,thusthepresenceofashdidnotappeartoaffecttheavailabilityofappliedNtotrees.Furthermore,neithervegetationseriesnorrocktypeaffectedthefertilization-inducedchangeinfoliarNconcentration.

Figure 9a—Six-year nitrogen (N) fertilization response (ft�ac –1yr –1) by base parent material and ash cap presence. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits (tert sed).



Figure 9d—Change in Douglas-fir foliar nitrogen (N) concentration (percent) following N fertilization as a function of control plot (unfertil-ized) foliar N concentration (percent).

Figure 9b—Six-year nitrogen (N) fertilization response (ft�ac –1yr –1) by base parent material and vegetation series. Parent materials include basalt, glacial deposit (glacial), granite and metasedimentary (metased). Vegetation series include Douglas-fir (DF), grand fir (GF) and western red cedar (WRC).

Figure 9c—Six-year nitrogen (N) fertilization response (ft�ac –1yr –1) as a function of soil mineralizable nitrogen (N, ppm).



Discussion ______________________________________________________

Ash distribution

Ashpresencegenerallyexplainedthesamevariationasgeographicregion,par-entmaterialandvegetationseries.Theconfoundingwithvegetationserieswasnotunexpected.Ithaslongbeenknown,forexample,thatwesternredcedarhabitattypesarehighlylikelytohaveashcap.ItisalsoknownthatashcapismorewidelydistributedinnorthIdaho,northeastWashingtonandnortheastOregonandlesscommonlyfoundincentralWashingtonandcentralIdaho.Theconfoundingofashpresencewithunderlyingparentmaterialtypeisperhapslessintuitive,butislikelyrelatedtothegeographicdistributionofthoseparentmaterials.Siteslocatedontertiarysedimentarydeposits,metasedimentaryrocksandglacialdepositsaremorelikelytooccurinnorthIdahoandnortheastWashington,whilesiteslocatedonbasalts,granites,moderndepositsandsedimentaryrocksaremorelikelytooccurincentralWashingtonandcentralIdaho.

Site Productivity

WhileSIwasavailableforonly110sitesandCGRforall139sites, thetwovariableswerehighlycorrelated(R2=0.59),suggestingthatbothvariablesbehavedsimilarlyasdescriptorsofsiteproductivity.Forbothvariables,ashpresenceatadepthof1inchorgreatersignificantlyincreasedsiteproductivityrelativetonon-ash sites. The increasewasgreater forCGR, suggesting that this variablewasamoresensitiveindicatoroftheeffectofashpresenceonsiteproductivity.However,additionalashdepthhadnoeffectoneitherofthesiteproductivityvariables.Thus,onceashwaspresent,itdidnotappeartomatterhowdeeptheashwasintermsofpredictingsiteproductivity.

Even though potentially available water was positively correlated with ashdepthandsiteproductivity,siteproductivitywasunaffectedbyincreasingashdepth.Thismeantthatsomethingabouttheashbesidespotentiallyavailablewaterwasaffectingsiteproductivity.Decreasednutrientavailabilitywasonepossiblefactorlimitingsiteproductivity.Foliageandsoil-availableMgandCagenerallydecreasedwithincreasingashdepth.Decreasedavailabilityoftheseelementsonsiteswithdeeperashcapscouldhelpexplainthelackofacorrespondingincreaseinsiteproductivityeventhoughpotentiallyavailablewaterwashigheronsuchsites.PositiverelationshipsbetweenashandnutrientavailabilityofB,PandKsuggestedthat theseelementswerenotlikelygrowth-limitinginthepresenceofash.

Site Fertility

Soil Moisture—Potentialavailablewaterisadescriptorofthecapabilityofasitetoretainandsupplymoisturetotheplantsgrowingonthatsite.Potentiallyavailablewaterincreasedwithincreasingashdepth,asseemedreasonablebasedonourexperiencewithash-capsoils.ThefindingthatpotentiallyavailablewaterwasgreateronwesternredcedarseriesthanongrandfirorDouglas-firseriesalso seemed reasonable, given that most western red cedar sites occurred inconjunctionwithash-capsoils.However,variationinpotentiallyavailablewaterbyvegetationseriesandashdepth(fig.3b)suggestedthatsitesonwesternred



cedarvegetationseriesstillhadhigheravailablewaterthansitesongrandfirorDouglas-fir series evenafter accounting for ash.Thus, somethingbesides ashpresenceanddepthaffectedpotentiallyavailablewaterandtheresultingvegeta-tionseries.Factorsbesidesashlikelytoaffectsoilmoistureandvegetationseriesareclimate,soiltemperatureregime,soildepth,soiltexture,parentmaterialandtopographicposition(slope,aspect,andelevation).

Someofthevariationinpotentiallyavailablewateramongparentmaterialsinthepresenceofashlikelyreflecteddifferencesinunderlyingsoiltextureaswellasashdepth.Basaltandmetasedimentaryrocksweathertofinersize-classsoilswithinherentlyhigherpotentialmoistureavailabilitycomparedtothecoarser-grainedandmorepermeable soilsderived fromgranitic rocksandglacialde-posits.However,theinteractionbetweenashpresenceandparentmaterialwaslesseasilyexplained.Sitesongraniticrocksandglacialdepositsshowedhighermoistureavailabilityintheabsenceofashthaninthepresenceofashallowashlayer(fig.3c).Sitesongraniticrocksneededabout7inchesofashandglacialsitesabout16inchesofashtoachievethesamepotentiallyavailablemoistureasthenon-ashsitesonthesesamerocktypes.Aftermeetingthesethresholdlevels,potentiallyavailablemoisturecontinuedtoincreasewithincreasingashdepthonbothrocktypes.Perhapssomedegreeofsoilmixingoccurredbetweenashandtheunderlyingresidualsoilsthatnegativelyimpactedmoisture-holdingcapacityattheshallowerashdepths.

Soil Acidity—SoilpHtendedtoincreasewithincreasingashdepth.However,acomplexrelationshipbetweenparentmaterialandashdepthsuggeststhatthisincreasewasdrivenprimarilybydatafromsitesongraniticandbasalticsubstrates,whereincreasingashdepthledtoincreasedpH.Onallotherparentmaterials,whichweresedimentaryinorigin,ashdepthhadnoeffectonsoilpH.Therea-sonsforthisbehaviorarenotentirelyclear.SoilpHlevelsoftheresearchsitesincludedinthisstudywerewithinarangewherenutrientavailabilityanduptakeofappliedfertilizerelementsshouldnotbeadverselyaffected.

Nitrogen—FoliarandsoilmeasuresofNavailabilitysuggestedthatNwasaffectedbyparentmaterial,butunaffectedbyashpresenceordepth.Soilmineraliz-ableNandavailableammonium-Nwereconsistentlyhigheronmetasedimentaryandtertiarydepositsitesandlowerongraniticandbasalticsites.Incontrast,foliaranalysessuggestedthatNuptakewasgreatestonsiteswithbasaltparentmaterials.Thissuggeststhattreesgrowingonbasaltparentmaterialswerebet-terabletotakeadvantageofsoil-availableNthantreesonotherrocktypes,orconverselythattreesonmetasedimentaryandtertiarysedimentarydepositswerelessabletoutilizesoil-availableN.

Reasonsforthecontrastingeffectsofparentmaterialonsoil-availableNpoolswerenotclearfromthisanalysis.ParentmaterialcouldpositivelyaffectNsupplybyimpartingsoiltexturalorchemicalconditionsthatareconducivetoincreasedN-mineralizationrates.Conversely,parentmaterialmaynegativelyaffectplantuptakeofNthroughintroductionofamoresignificantgrowth-limitingfactor,suchaslowmoistureavailability(affectedbysoiltexture)orlownutrientavailability(affectedbyparentmaterialmineralogy).EitherscenariocouldcontributetoanincreaseinthesoilmineralizableNpool.MineralizableNwasstronglycorrelatedwithsoilorganicmatterandsoilcarbon,suggestingthatN-mineralizationrateswerealsogovernedbyorganicmatteravailability.Climaticconditionsmayaffectorganicmatterproductionbyaffectingproductivityand/orbyaffectingconditions



conducivetoNmineralization.WhilefoliarNwasonlyweaklycorrelatedwithmineralizableN,itwasnegativelycorrelatedwithelevation,suggestinggreaterNavailabilityonwarmer,lowerelevationsites.Othersitefactorsincludingsitefertility,soilwaterpotentialandtopographicfactorshadnoeffectonfoliageNconcentrations.

Cations—LikeN,cationswerealsoaffectedbybaseparentmaterials,thoughinamorepredictablefashion.Intheabsenceofash,soil-extractableCaandMgconcentrationsintheupper12inchesofsoilwerehigheronbasaltparentmaterialsandlowerongranites.BecausebasaltsarehigherinCa-andMg-bearingmineralsthangranites,thisfindingisplausible.However,onceashwaspresent,availableCaandMgdecreasedwithincreasingashdepthonbothbasaltsandgranites.ThissuggeststhatCaandMgstorageinashispooreveninthepresenceofCa-andMg-richunderlyingparentmaterials,andthatsoilCaandMgavailabilitymaybeloweronsiteswithdeeperashcaps.Thismayreflectthedilutionofresidualsoilswithincreasingashpresence,andaresultingdilutionofCaandMgpoolsintheupper12inchesofsoil.Foliarchemistryalsosuggestedthatplantuptakeofbothelementsdecreasedatincreasingashdepths.

IncontrasttoCaandMg,soil-extractableKwasunaffectedbyashpresenceordepth,andwasonlyaffectedbyparentmaterial.Theparentmaterialeffectwasdrivenbybasalt,whichshowedhigherextractableKthanotherrocktypes.However,foliarKwasunrelatedtoparentmaterial,andwaspositivelyaffectedbyashpresence(butnotaffectedbydepth).Thelackofarelationshipbetweensoil-extractableKandfoliarKcouldindicatethateitherthesoilorfoliartestforKwasinadequate.TheseresultscouldalsosuggestthatashpresencesomehowfacilitatedtreeuptakeofK,eventhoughsoil-extractableKappearedunaffectedbyashpresence.ThismayalsobeanindicatoroflowcationretentionbyashsoilsandthehighmobilityoftheK+ion.

Phosphorus—DespiteconcernsofpossiblePadsorptionbyashsoils,soilandfoliartestssuggestedthatPavailabilityanduptakewereunaffectedbyashpresenceordepth.Onallsites,foliarPconcentrationswereatorabovenutritionalcriticallevels,suggestingthatsufficientPwasavailablefortreegrowthandfunction.

Boron, Cu and S—Boronshowedincreasingsoilavailabilityandfoliarconcen-trationwithincreasingashdepth.ThispositiverelationshipsuggeststhatashmayprovideefficientstorageforB,andalsothatashdoesnotadsorbBtoanextentthatmakestheBunavailableforplantuptake.AshdidnotaffectsoilorfoliarCuvalues.Soil-availableCushowedsomevariationbyparentmaterialthatwaslikelyrelatedtotracemineralsinthevariousparentmaterials.However,therewaspooragreementbetweensoil-availableandfoliarCuconcentrationsinthatfoliarCushowednocorrespondingparentmaterialeffect.Soil-availableSwasunaffectedbyashpresenceordepth,orbyparentmaterial.

Fertilization Response

Nitrogen—Overall,volumegrowthresponsetoNfertilizationwasmuchbetteronsiteswithashthanonsiteswithout.IncludingbaseparentmaterialinthemodelwithashcontributedanadditionaldegreeofpredictabilityofvolumeresponsetoNfertilization.Ashwasparticularlyvaluableinincreasingfertilizationresponseonthesedimentarydeposits(includingglacialdeposits)andsomewhatlesssoonthebasalt,graniteandmetasedimentaryrocks.



TherelationshipoffertilizationresponsetosoilmineralizableNsuggestedthatthelowerthemineralizableN,thehigherthefertilizationresponse.Thissupportsthe idea thatN-deficient sites should showahigherdegreeof response toNfertilization.Similarly,thechangeinfoliarNconcentrationfollowingfertilizationshould indicate theeffectivenessof the fertilization treatment inchanging theamountofNavailabletothetreesforgrowth.However,unfertilizedfoliarNcon-centrations,whileinverselyproportionaltothechangeinfoliarNconcentrationfollowingNapplication,didnotshowanyrelationshiptofertilizationresponse.Thus,whilelowerfoliarNlevelswerepredictiveofagreaterincreaseinfoliarNafterfertilization,theywerenotnecessarilypredictiveofagreaterNfertilizationresponse.IncreasesinfoliarbiomassfollowingNfertilizationhavebeenshowntobemorepredictiveoffuturevolumeresponsethanchangesinNconcentrationalone(WeetmanandFournier1986;HasseandRose1995;Brockley2000).

Sulfur and K—SiteswithashgenerallyrespondedbettertoSfertilizationthanthosewithout.However,onceashwaspresent,thetrendwasdecreasingresponsewithincreasingashdepth,suggestingpossibleSadsorptionbyash-capsoils.Noevidencewas foundtosuggest thatashpresenceaffectedgrowthresponseorfoliarKstatusfollowingKfertilization.

Nutritional Characteristics of Ash

Anionadsorptionmaybeanissueofconcerninashsoilsduetothecharacter-isticvariablechargeofash(McDanielandothers2005;Kimseyandothers2005).ThedecreaseintreegrowthresponsetoSfertilizationwithincreasingashdepthsuggestspossiblesulfateretentionbyashsoils.HowevernoevidenceofnitrateretentionappearedfollowingNapplicationasureaorammonium.Foliar testssuggestedthatappliedNwastakenupbythetrees,and6-yeargrowthresponsesuggeststhatN-fertilizationdidincreasebiomassandvolumeproduction.Phos-phorusandBwerenotappliedduring these fertilization trialsbecause foliagetestsindicatedthattheseelementswerenotdeficient.Ourresultsalsosuggestedthatashdidnothaveanyeffectonsoil-availableorfoliarP,implyingthatPisnotlikelyagrowth-limitingelementonash-capsoils.Boronavailabilityappearedtoincreasewithincreasingashdepthaccordingtobothsoil-availableandfoliagetests.WhileinsufficientdatawereavailabletotestforthefateofBfollowingap-plication,Badsorptiondidnotseemtobeagrowth-limitingcharacteristicofashsoilsduringthisanalysis.

Theinabilityofpure,unweatheredashtostoreandsupplycationsmayalsobeanissueofconcerninandicsoils(McDanielandothers2005).Despitethedegreeofmixingandweatheringexhibitedbytheash-capsoilsinourstudy,storageandsupplymaystillhavebeenanissueforMg2+andCa2+.Bothelementsshoweddecreasedsoilavailabilityandfoliarconcentrationwithincreasingashdepth.ThisoccurredevenwhentheunderlyingparentmaterialswerehighinCaandMg,suggestingpossibledilutionofresidualsoilnutrientpoolsbyash.Incontrast,soil-extractableKwasunaffectedbyashpresenceordepth,andwasonlyaffectedbyparentmate-rial.Thus,ashsoilsappearedcapableoftakingontheKcharacteristicofunderlyingparentmaterial,butnottheCaorMgcharacteristic.ThiscouldoccurbecauseK+isamoremobileionandislikelytobetakenupbyplantsanddepositedonthesoilsurface.Also,foliarKwaspositivelyaffectedbyashpresence,suggestingthatashsoilswerebetterabletosupplyK,thoughnotnecessarilystoreit,comparedtonon-ashsoils.Thus,cationstorageandsupplyornutrientpooldilutionofthe



divalentcationsappearedpotentiallyproblematicinashsoils,whilethemonovalentKionwaslessaffectedbyashretentionanddilutionissues.

Management Recommendations _________________________________Site Nutrition and Nutrient Management

“Nutrient management” refers to silvicultural activities as they affect thenutrientcapitalofaforeststand.Itcanincludefertilizationtreatmentsandac-tivitiesthatretainnutrientsonsiteduringsilviculturalactivities.Becausemostnutrientsareheldinlimbsandfoliage(Coleandothers1967;Pangandothers1987;Millerandothers1993;Moller2000),aconservativenutrientmanage-mentstrategywouldbetoleavethetopsandlimbsofharvestedtreeson-sitethroughavarietyofbole-onlyharvestingtechniques.Whole-treeoperationsinlatefallandwinter,whenbreakageismorelikely,shouldalsobeeffectiveatretainingsomenutrientsonthesite.Speciesdifferinnutrientdemand(Gordon1983;Gowerandothers1993;Millerandothers1993;Mooreandothers2004).Therefore,plantingnutritionallychallengedsiteswithless-demandingspeciesand favoring less-demanding species during silvicultural operations are alsoconservativenutrientmanagementstrategies.

Testsoffoliageandsoilchemistrymaybeperformedassitespecificindicatorsofproductivityandpotentialfertilizationresponse.FoliarNwasabetterpredictorofsiteproductivity,whilesoilmineralizableNwasabetterpredictoroffertilizerresponse.Ifsatisfactoryinformationonsiteproductivityisavailableandtheparentmaterial/ashcombinationsuggeststhatthesitemayberesponsivetofertilization,managersshouldconsiderfocusingontestsofsoilmineralizableN.Ifmineraliz-ableNisbelow70ppm,thesiteshouldshowa6-yearvolumeresponseof10%ormore,withthepotentialresponseincreasingasmineralizableNdecreases.FoliarNmaybetestedasanindicatorofoverallsiteproductivity;however,theeffortandexpenseofthistestmakeitlessdesirablethanperformingsimplesiteheight/agemeasurements.

Nutrient Management Recommendations by Parent Material and Ash Presence

Basalts, Glacial and Modern Deposits—Sitesonbasalts,glacialdepositsandmodern sedimentarydeposits showednochange in siteproductivity in termsofCGRinthepresenceofash.Howeverthesesitesdidshowmoderate(basaltandmodernsedimentary)tohigh(glacialdeposit)increasesinvolumegrowthresponsestoNfertilizationwhenashwaspresent.ThissuggeststhatsitesontheseparentmaterialsshouldrespondreasonablywelltoNfertilizationwithoutash,andrespondevenbetterwhenashispresent.Therewasweakevidencethatonbasaltparentmaterials,thepresenceofashinhibitedvolumeresponsetoSfertiliza-tion.However,otherIFTNCstudieshaveshownthatSissometimesnecessarytostimulateagrowthresponsetoNfertilizationonbasaltparentmaterials(Garrisonandothers2000).WhileallparentmaterialsinthiscategoryshouldrespondwelltofertilizationwithNonly,strongergrowthresponsesmightbeinducedbymulti-nutrientfertilizationthatincludesS.Conservativenutrientmanagementstrategiesshouldbeevaluated,butmaybelesscrucialontheseparentmaterialscomparedtootherparentmaterials.



Metasedimentary and Granite—Metasedimentaryparentmaterials showedrelatively lower site productivity and granites showed moderate productivitycomparedtootherparentmaterials.Siteproductivityincreasedinthepresenceofashonbothparentmaterialtypes,withmetasedimentaryproductivitydoublingintermsofCGR.However,N-fertilizerresponsewasunaffectedbyashpresenceforeitherparentmaterial.Thissuggeststhat(1)treesgrowbetteronmetasedimentaryandgraniticrockswhenashispresent,and(2)fertilizationwithNalonewillnotincreaseproductivityonashsitesoverthatofnon-ashsitesonmetasedimentaryorgraniticrocks.TherewasweakevidencethatmetasedimentaryandgraniticsiteswithashmayrespondpositivelytoSfertilization.Preliminaryresultsofre-centfertilizationscreeningtrialsonbothparentmaterialtypesshowedgenerallypoorgrowthresponsetofertilizationwithNalone,andstrongerresponsetoacombinedtreatmentofN,K,S,andBwhenashwaspresent(Garrison-Johnstonandothers2005,unpublisheddata).Thus,multinutrientfertilizationismorelikelytostimulategrowthresponseonashsoilsonmetasedimentaryandgraniticparentmaterials.Generalnutritionalchallengesofthesesitessuggestuseofconservativenutrientmanagementstrategies.

Tertiary Sedimentary Deposits—Tertiarysedimentaryparentmaterialsbehavedsomewhatdifferentlythantheotherparentmaterialsinthatbothsiteproductiv-ityandNfertilizationresponsewereenhancedinthepresenceofash.Becausetheavailabledatafortertiarysedimentarysiteswassparse,theseresultsforthisdeposittypeshouldbeviewedcautiously.However,thissuggeststhatifstandsontertiarysedimentsaregrowingwell,theyshouldrespondwelltoNfertilizationintheabsenceofash,andevenbetterwhenashispresent.Somecautionshouldbeexercisedinapplyingfertilizer,however,asfieldexperiencehasalsoshownthattertiarysedimentarydepositscaninherentlybequitevariableincomposition.Pendingfurtherinvestigation,useofconservativenutrientmanagementstrategiesisalsorecommended.

Conclusions _____________________________________________________Standproductivitywasgreateronsiteswithashcapthanonsiteswithout;how-

everonceashwaspresent,changesinashdepthdidnotaffectsiteproductivity.Becauseashpresenceorabsencetendedtocoincidewithparticularvegetationseriesandgeographicregions,ashpresencedidnotfurtherexplainvariationinsiteproductivitybeyondthatdescribedbythosevariables.Whileashpresencealsotendedtocoincidewithparticularparentmaterialtypes,ashpresencestillexplainedsomevariation insiteproductivitybeyond thatexplainedbyparentmaterial.Ashpresencewasmostlikelytoincreasesiteproductivityonmetasedi-mentaryrocks,granitesandperhapstertiarysediments.

Althoughsiteproductivitywaspositivelycorrelatedwithpotentiallyavailablewaterandpotentiallyavailablewaterwaspositivelycorrelatedwithashdepth,therewasnocorrelationbetweensiteproductivityandashdepth.Thissuggeststhatsomethingelseabouttheash,suchaspoornutrition,affectedproductivity.Soil-availableandfoliarMgandCadecreasedwithincreasingashdepth.Thus,whileincreasingashdepthmayhaveapositiveeffectonsoilmoisturepotential,itmayhaveanegativeeffectonnutrientavailability,particularlyforMgandCa,andthereforeonsiteproductivity.



SoilNavailability (mineralizableandammonium)and foliageNconcentra-tionswerenotaffectedbyashpresenceordepth,butwereaffectedbyparentmaterial.Reasonsfortheparentmaterialeffectwerenotentirelyclear,howeverthesiteproductivityandsoil texturalandchemicalconditionsassociatedwithparticularunderlyingparentmaterialslikelyaffectedorganicmatterproductionandcycling.SoilorganicmatterandcarboncontentwerehighlycorrelatedwithsoilNavailability.ClimateandelevationlikelyinteractedwithparentmaterialstohaveaneffectonNavailability,aswell.

Possiblenutrientadsorptionandsupplybyashwerealsoconsidered.AdsorptionofappliedNdidnotappeartooccurinash-capsoilsinthisstudy.Incontrast,decreasing growth response to S-fertilization at greater ash depths suggestedthatadsorptionofappliedSmayhaveoccurred.Foliageandsoil-availabilityofPandBeithershowednochange(P)orincreasedavailability(B)withincreasingashdepth,suggestingthatavailabilityoftheseelementsmaynotbeanissueofconcerninash-capsoils.LackofsoilMgandCastorageandsupplyatgreaterashdepths,orperhapsdilutionofMgandCasupplybyincreasingquantitiesofash,didappeartooccur.SoilKwasunaffectedbyashpresenceordepth,whilefoliarKconcentrationsincreasedwhenashwaspresent,suggestingthatKsupplywasperhapsenhancedbyashpresence.

Averagevolumeresponse toN fertilizationwasalmost50%greateronashcomparedtonon-ashsites.Howeverchangesinashdepthdidnotfurtheraffectvolumeresponse.AshpresenceincreasedvolumeresponsetoNfertilizationonglacialdeposits, tertiarysediments,modernsedimentsandbasalts,butnotongraniteormetasedimentaryparentmaterials.Volumeresponsewasgreatestonwesternredcedarvegetationseries,followedbygrandfirandthenDouglas-firvegetationseries.Howeverashpresenceordepthdidnotfurtheraffectvolumeresponseoncevegetationserieswasknown.Parentmaterialcombinedwithveg-etationseriesbestdescribedvolumeresponsetoN-fertilization.

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Han-Sup Han is an academic faculty, Forest Products Department, College of Natural Resources, University of Idaho, Moscow.

Abstract Economic implicationsof soildisturbancearediscussed in fourcategories:planningand layout,selection of harvesting systems and equipment, long-term site productivity loss, and rehabilitationtreatments.Preventivemeasuresaremoreeffectiveinminimizingimpactsonsoilsthanrehabilitationtreatments becauseof the remedial expenses, loss of productivity untilmitigationoccurs, and thepossibilitythatoriginalsoilconditionsmaynotberestored.Alternativeharvestingpracticesthataredesignedtominimizeimpactsonsoils,suchasuseofdesignatedskidtrailsandwidetrail-spacing,increaseoverallharvestingcosts.Siteswithhighriskforsoildisturbancemayrequireuseofexpensivewoodextractionmethods(e.g.,skylineyarding),asopposedtolowercostoptions(e.g.groundskidding).Tillagetreatmentsinseverelycompactedareasappeartobecosteffectiveifproperlyimplemented.Anaccurateestimationofeconomicconsequencesfromlong-termsiteproductivitylossesisdifficult,althoughthereisageneralconsensusthatsoildisturbanceatsomelocationscanreducetreegrowth.

Economics of Soil Disturbance

Han-Sup Han

Introduction

Questionsontheeconomicsofsoildisturbanceareoftenraisedregardinglong-termpro-ductivitylosses,effortstominimizesoilimpacts,andrehabilitationofdamagedsoils.Whatarepotentialfinancialimpactsfromsiteproductivitylosses?Shouldwerequireeveryground-skiddingmachineonhigh-risksitestousedesignatedskidtrailsandhowdoesthisaffectloggingcosts?Woulditbecost-effectivetoamelioratecompactedsoils?Arewefinanciallygettingasignificantbenefitfromsoilrehabilitationtreatments?Thesequestionshavenotbeenextensivelyansweredbecauseofthedifficultyinobtainingappropriatedataabouttreeresponsestositedisturbanceacrossanentirerotation,thevalueofoffsiteimpacts,andotherpertinentinfor-mationsuchaspreventiveandremediationmeasures(Lousier1990;Millerandothers2004).


Han Economics of Soil Disturbance

Lackofinformationontheeconomicsofsoildisturbancelimitsforestpraction-ersfromattemptingtodevelopharvestingplansandtimbersales.Aharvestingplanneedstoaccountforsoildisturbancerisks,previousimpactsonsoils,andpreventivemeasuresthatminimizefurtherdamagetosoils.Preventivemeasuresmayrequirecableloggingsystemsongentleslopes(<30percent)orwiderspacingofdesignatedskidtrails,buttheseoftenresultinhigherloggingcosts.Lackofcompellingevidencetojustifythesehighloggingoptionsoftencausesdisagree-mentsamong forestmanagers,although there isageneralconsensus that soildisturbancemayreducetreegrowthatsomelocations(Millerandothers2004).Onewouldalsowonderifthesepreventivemeasureswouldfinanciallybenefitlandownersinthelongrun.

Thispapersummarizeseconomicinformationrelatedtosoilimpactsinfourcategories:planningandlayout,selectionofharvestingsystemsandequipment,long-termsiteproductivityloss,andrehabilitationtreatments.Inthispaper,soildis-turbancesincludesoilcompaction,scalping,puddling,andsoildisplacement.

Planning and Layout: Measures to Prevent Soil Disturbance _________Soildisturbancefromtimberharvestingmaynotbeavoidable,butcanbemini-

mizedthroughcarefulplanningandoperations.Preventivemeasuresaremoreeffectiveinminimizingimpactsonsoilsthanremedialmitigationbecauseoftheremedialexpenses,lossofproductivityuntilmitigationoccurs,andthepossibilitythatoriginalsoilconditionsmaynotberestored(Millerandothers2004).Exist-ingguidelinesandrequirementsforsoilprotectionshouldalwaysbeobservedwhentheharvestingplanisdeveloped.Agoodharvestplancanminimizesoildisturbance by recognizing and identifying the risk of soil disturbance. Someimportantfactorsdetermining“riskrating”includesoiltexture,moisturecontent,slope,andorganicmaterialsatthetopsoil.

Planningandlayoutcomponents for timberharvestingincludelocations forroadsandlandings,markingtreestocutorleave,andflaggingskidtrailsorsky-linecorridors.Thesevarywithdifferentharvestingsystems.Forexample,skylineyardingrequireslocatinganchorsforriggingandground-profileanalysisforavail-abledeflection,causinghigherplanningandlayoutcostsforcableloggingthanground-basedharvestingsystem.Kelloggandothers(1998)comparedplanningandlayoutcostforloggingcontractorsinvarioussilviculturaltreatments.TheyfoundthataCTLsystemusingamixofrandomanddesignatedskidtrails(60-ftspacing)hadthelowestcost,followedbythetractor-basedwinchingsystemforhand-felledtreesthatused130-ftspacingdesignatedskidtrails.Theskylinesys-temshadthehighestcost.

Useofdesignatedskidtrailshasbeenrecommendedinpastsoilcompactionstudiesbecauseiteffectivelyreducestheskidtrailareasinaharvestingunitandfacilitatesrehabilitationefforts(AndrusandFroehlich1983).Designatedskidtrailsatawidespacingincreaseloggingcosts.Inanearlierstudy(Bradshaw1979),theharvestunitwithpre-plannedskidtrailsandwinchinghada29percenthigherskidcostthantheconventionallyharvestedunit.However,only4percentofitsareawasinskidtrails,comparedto22percentfortheconventionallyharvestedunit.

Thereareotherplanningandlayoutcomponentsthatincreasecosts,butaredifficult to estimate. These include expenses related to evaluating soil distur-bancerisks, identifyingareasinthefieldthatposeahighriskforsoildamage


Economics of Soil Disturbance Han

anderosion,anddevelopmentstrategiesandguidelinestominimizesoilimpact.Delayingloggingoperationstodryseasonsorwinterseasonloggingandstrictrequirementsforbestmanagementpractices(BMP)areexamplesforpreventiveeffortsataplanningstage.Theseexpensesusuallyoccurintheformofoverheadoradministrativecostandcanbeestimatedbasedoncompaniesoragencies’indirectcostrates.

Selection of Harvesting Systems and Equipment ___________________Because harvest equipment creates ground pressures and soil disturbance

types(e.g.,compactionandscalping),choiceofharvestingsystemsandequip-menttypecangreatlyaffectthedegreeandextentofsoilimpacts.Cablesystemsareoftenpreferredoverground-basedsystemsbecausecableloggingdoesnotrequireheavymachinesmovingonharvestingareas.Logsarefullyorpartiallysuspendedtotheskylineandpulledtothelandings.Allen(1997)reportedthataskylinethinningoperationinwesternOregonleftonly2percentofsoildistur-bancewhileasingleentryofcut-to-length(CTL)systemcaused25percentoftheharvestareacompacted.

However,cableloggingistypicallymoreexpensivethanaground-basedsystem:cableyardingcostsare65to160percenthigherthanconventionalground-basedlogging(Lousier1990).Forexample,Keeganandothers(1995)surveyedstump-to-truckharvestcostsintheMontanaandnorthernIdahoregionandfoundthatthecostforground-basedsystemswaslowest($87to$124/thousandboardfeet(MBF)), followedbycablesystemsranging from$13 to$164/MBF.Helicoptersystemsweremostexpensiveat$233/MBF.Comparedtomechanizedground-basedsystems,cable loggingrequiresmore labor tomanuallyhandle treesorlogsonsteepgrounds(typically>30percentslope)aswellastoset-upandteardownanentireyardingsystem,whichresultsinlowdailyproductionoftimber.Timespentchangingskylineroadsandriggingalsocontributestohighcostsincable logging. High logging costs in cable logging becomes more noticeablewhenhandlingsmall-diametertrees.Ataverage10-inchdiameteratbreastheight(DBH),skylineandhelicopterstump-to-truckloggingandchippingcostswereabout3and6timesmoreexpensive,respectively,comparedwithamechanizedwhole-treeharvestingsystemthatshowedthelowestcostat$34.23/100cubicfeet(Hanandothers2004).

Cableyarding,combinedwithmechanizedfellingandprocessing,hasbeenconsideredasawayof reducing soil compactionandother typesof soildis-turbance from the ground skidding or forwarding phase of timber harvesting.Althoughmechanizedfellingandin-woodsprocessingusingafeller-buncheroraharvesterhaveinsignificantimpactsonsoils,subsequentgroundskiddingandforwardingcausesignificantincreaseinsoilbulkdensity(Allen1997).Theques-tionishowmuchmoreexpensiveitistouseskylineyardingthanground-basedskidding.Johnson(1999)reportedthatcableyarding($0.51/ft3)resultedin113percentcost increaseover forwarding ($0.24/ft3)of logs felledandprocessedbyaCTLharvester.However,theaverageforwardingdistance(212ft)forcableyardingwasmuchlongerthattheone(129ft)withforwarding.Thismaylowerthe roaddensity required for timberharvestingactivitiesand reduce theareaofsoilsdisturbed.IneasternOregon,askylineyarderwasusedtoextractlogsprocessedbyaCTLharvesterinanefforttoavoidfurtherdamagetosoilfrom



fuelreductionthinningonslopesthataveraged12percentorlessonallunits,withmaximumsof25percent(Drewsandothers2000).Theyreportedthattheharvester-yardersystemaveragedmuchhigher($80/greenton)stump-to-millcoststhantheharvester-forwardersystem($46/greenton).

Lowground-pressuremachines,suchaslogloadersandwide-tiredskidders,forwoodextractionfromstumptolandingarealsooftenconsideredtominimizesoilcompaction.Shovelloggingusesahydrauliclogloadertorepeatedlyswingthelogstoreachtheroadorlandingarea,andhasbeenusedasanalternativetoacablesystemonmoderategrounds(20to40percentslope)oraground-basedsystemongentleslopes(<20percent).TheaverageunitproductioncostforshovellogginginwesternWashingtonwas40percentlessthantheonewithcableloggingatanaverageexternalyardingdistanceof600feet(Fisher1999).Useofaskidderequippedwithwidetirestoreducegroundpressurehasbeenusedbymachinerymanufacturersasmachineshaveincreasedinsizeandweight(Brinkerandothers1996).Paststudiesindicatedthatwidertiresresultedin13to23percentincrease(Meek1994)ornosignificantdifference(Klepacandothers2001)inskiddingcost.Klepacandothers(2001)alsonotedthatloggersarere-luctanttousewidetiresbecauseofadditionaloverhangduringmachinetransportfromonesitetoanother,andrequirementforahighertorque,heavy-dutyrearaxleintheskidder.

Whenselectingamechanized,ground-basedsystemfortimberharvesting,aCTLsystemisoftencomparedwithawholetreesystemconsistingofafeller-buncher,skidder,aprocessor,andaloaderforitsharvestingproductivityandcost.Whileproductionratesandcostsforthesetwosystemsarecomparable(Hartsoughandothers1997;LanfordandStokes1996;Gingras1994),impactsonsitescandif-fersignificantly(LanfordandStokes1995;Gingras1994).ACTLsystemisoftenfavoredoverawhole-treeharvestingsystembecauseaharvesterprocessestreestologlengthatthestump,leavingallbranchesandtreetopsonsite.Aforwarderdrivesovertheslashmat,andthishelpstominimizeimpactsonsoils.

Long-term Site Productivity Losses _______________________________Aconcernforsiteproductivitylossesaftersoildisturbancefromtimberharvesting

activitiesisaprimaryreasonforimposingstrictrequirementsforsoilprotectioninthecontextofsustainableforestry.Somestudieshaveshownthatsoilcompactionadverselyimpacttreegrowth.However,estimationofactualorpossibleproductivitylossesresultingfromsoildisturbanceisacomplicatedissuebecauseofdifficultiesofaccurateestimationofsoildisturbancesconsequencesontreegrowth(Millerandothers2004;Heningerandothers2002;Lousier1990;Helmsandothers1986).Millerandothers(2004)suggestedthatforecastsofreducedtimberyieldfromdegradedsoilsareuncertainbecausetreeresponsetosoildisturbanceisgreatlyaffectedbyothersite-specific,growth-determiningfactors.

In addition to tree’s biological and physical responses to soil disturbances,discountratesalsohavesignificantimpactontheoveralleconomicanalysisofsoildisturbances;theanalysisperformsovertheentiretreerotationperiodanddiscountratesaregreatlysensitivetotime.Stewartandothers(1988)developedaneconomicmodel thataddressed financial impactsofsoilcompactiononalong-termbasis.Themodeluseda stand-growth simulatorand includedvari-ousscenariosofmanagementoptions.Ata4percentdiscountrate,net-presentvalueanalysisshowedpositivevalues,thusencouragingpreventiveefforts(wide



trailspacing)andindicatinghigheraffordabilityforcarefullogging.Underanas-sumptionthattreeyieldwasreducedon100percentofskidtrailareas,thenetpresentvalue(NPV)with4percentwas$504/acwhileitwas$144/acwith8percentdiscountrate.Onecouldaffordtospendanextra$144/actoavoidtheseyieldreductions.

Rehabilitation ___________________________________________________Soilrehabilitationinvolvesmechanicalmeasures(e.g.tillage)tobreakupse-

verelycompactedsoils.Ithelpspromotewaterandairmovement(AndrusandFroehlich1983)andincreasenutrientavailability(Millerandothers2004)inacompactedsoil.Theefficacyoftillageinlooseningcompactedsoilsdependsonequipmenttypesusedandsoilproperties(UngerandCassel1991;AndrusandFroehlich1983),numberofmachinepasses(AndrusandFroehlich1983),andtillagedepth (McNabbandHobbs1989).Theoverallcostof tilling isdirectlyinfluencedbythesefactors.

AndrusandFroehlich(1983)studiedproductionratesandcostsforskid-trailtillageatselectedsitesinOregonandWashington.Fourtypesoftillageequipmentwereevaluatedinthestudy:diskharrow,rockripper,brushblade,andwingedsubsoiler.Productionrateswerehighestwhentillingwithonepassofthemachine.Uphilltillingonsteepgroundsrequiredalargecrawlertractoratahighermachinecost.Thewinged subsoiler lossenedmore than80percentof thecompactedsoilinasinglepassandwasthemostcost-effectivetillagemethod(fig.1).Theauthorsindicatedthattillageresultsforthesesiteswouldhaveimprovedifthetill-ageimprovementhadmadeadditionalpassesalongtheskidtrails,butadditionalpasseswouldincreasethecostoftilling.

Figure 1—Tillage costs and rates for various type of tillage equipment (Andrus and Froehlich 19��)



Ifproperlyimplemented,tillagemaybecost-effectiveunderthemostextremecompaction situations, such as landing areas and heavily traveled skid trails.Stewartandothers(1988)estimatedthejustifiableincreasedcostforhigh-costloggingorrehabilitationperharvestentrywith125-ftskidtrailspacing.Thenetfinancialbenefitfromtillagewasnotablyaffectedbydiscountratesandsiteindexandrangedfrom$86/acto$284/ac.Thisrangeofjustifiablecostsis farmorethanacostestimate($20/acor$176/mile)forskidtrailrestorationwithawingedsubsoilermountedbehindCatD6Ccrawlertractor(FroehlichandMiles1984).

Conclusion ______________________________________________________Economicsofsoildisturbanceiscomplicatedandrequiresmeasuringeconomic

consequencesfromlong-termsiteproductivitylossesandexpensesforpreventiveandrehabilitationmeasures.Anaccurateestimationofsoildisturbancesconse-quencesontreegrowthisdifficultbecausethetree’sresponsetosoildisturbanceisaffectedbyothersite-specific,growth-determiningfactors.Manyassumptionsareneededtoestimatefuturegrowthandyieldandthesegreatlyaffectoverallfinancialanalyses.Althoughdirectcostsforpreventionandrehabilitationcanbeestimated,directandindirectfinancialbenefitsfromthesepracticesarenotwelldocumented.Majoruncertaintiesoriginatefromtherequirementforlong-termeconomicanalysisofunknownbiologicalimpactsfromsoildisturbanceandin-consistentdiscountratesusedintheanalysis.

Preventivemeasuresaremoreeffectiveinminimizingimpactsonsoilsthanrehabilitationtreatmentsbecauseofremedialexpenses,lossofproductivityuntilmitigationoccurs, and thepossibility that original soil conditionsmaynot berestored.Carefulplanningand layoutandselectionofharvestingsystemsandequipmentoftenincreaseoverallharvestingcosts.Alternativeharvestingprac-ticesthataredesignedtominimizeimpactsonsoils,suchasuseofdesignatedskidtrailsandwidetrailspacing,increaseoverallharvestingcosts.Rehabilitationexpensesareadditionaltotheseincreasedcosts.However,theseinitialexpensescanbejustifiedwhenpreventiveandrehabilitationmeasuresarefocusedonhighrisksitesandseverelydisturbedareas.Expensesforcarefulplanningandlayout,alternativeloggingpracticesandrehabilitationmeasuresshouldberecognizedaspartofoverallloggingcostestimationtosupporttheideaofminimizingimpactsonsoils.

Literature Cited __________________________________________________Allen, M. M. 1997. Soil compaction and disturbance following a thinning of second-growth

Douglas-firwithacut-to-lengthandaskylinesysteminOregoncascade.Corvallis,OR:OregonStateUniversity.105p.MSthesis.

Andrus,W.C.;Froehlich,H.A.1983.AnevaluationoffourimplementsusedtotillcompactedforestsoilsinthePacificNorthwest.Res.Bulletin45.Corvallis,OR:OregonStateUniversity.12p.

Bradshaw,G.1979.Preplannedskidtrailsandwinchingversusconventionalharvestingonapartialcut.Res.Note62.Corvallis,OR:OregonStateUniversity.4p.

Brinker,R.W.;Klepac,J.F.;Stokes,B.J.;Roberson,J.D.1996.Effectoftiresizeonskidderproduc-tivity.In:ProceedingsofaJointConferenceoftheCanadianWoodlandsForum,theCanadianPulpandPaperAssociation, and the InternationalUnionof ForestResearchOrganizations;1996September9-11;QuebecCity,Quebec.Montreal,Quebec:CanadianPulpandPaperAssociation:85-89.



Drews, E. S.; Doyal, J. A.; Hartsough, B. R.; Kellogg, L. D. 2000. Harvester-forwarder andharvester-yardersystemsforfuelreductiontreatments.Int.J.ofFor.Eng.12(1):81-91.

Fisher,J.1999.Shovellogging:costeffectivesystemsgainsground.ProceedingsofInternationalMountain Logging and10th PacificNorthwest Skyline Symposium;1999March28-April 1;Corvallis,Oregon:61-67.

Froehlich,H.A.;Miles,D.W.R.1984.Wingedsubsoiler tillscompacted forestsoil.For. Ind.111(2):42-43.

Gingras,J.-F.1994.Acomparisonoffull-treeversuscut-to-lengthsystemsintheManitobaModelForest.ForestEngineeringInstituteofCanada.SpecialReport,SR-92.16p.

Han,H.-S.;Lee,H.W.;Johnson,L.R.2004.Economicfeasibilityofanintegratedharvestingsystemforsmall-diametertreesinsouthwestIdaho.For.Prod.J.54(2):21-27.

Hartsough,B.R.;Drews, E. S.;McNeel, J. F.;Durston, T.A.; Stokes,B. J. 1997.Comparisonof mechinized systems for thinning ponderosa pine and mixed conifer stands. For. Prod. J.47(11/12):59-68.

Helms,J.A.;Hipkin,C.;Alexander,E.B.1986.EffectsofsoilcompactiononheightgrowthofaCaliforniaponderosapineplantation.West.J.Appl.For.1(4):104-108.

Heninger,R.;Scott,W.;Dobkowski,A.;Miller,R.;Anderson,H.;Duke,S.2002.Soildisturbanceand10-yeargrowthresponseofcoastDouglas-fironnontilledandtilledskidtrailsintheOregonCascades.Can.J.For.Res.32:233-246.

Johnson,L.R.1999.Combiningcut-to-lengthandcableyardingoperation.ProceedingsofInter-nationalMountainLoggingand10thPacificNorthwestSkylineSymposium;1999March28-April1;Corvallis,Oregon:42-52.

Keegan,C.E.;Fiedler,C.E.;Wichman,D.P.1995.CostsassociatedwithharvestactivitiesformajorharvestsystemsinMontana.For.Prod.J.45(7/8):78-82.

Kellogg,L.D.;Milota,G.V.;Stringham,B.1998.Loggingplanningandlayoutcostsforthinning:experiencefromtheWillametteYoungStandProject.Res.Contribution20.OregonStateUni-versity,CollegeofForestry.12p.

Klepac, J.; Stokes,B.;Roberson, J.2001.Effectof tire sizeon skidderproductivityunderwetconditions.Int.J.ofFor.Eng.12(1):61-69.

Lanford,B.L.;Stokes,B. J.1995.Comparisonof two thinning systems.Part1.Standand siteimpacts.For.Prod.J.45(5):74-79.

Lanford,B.L.;Stokes,B.J.1996.Comparisonoftwothinningsystems.Part2.Productivityandcost.For.Prod.J.46(11/12):47-53.

Lousier, J.D.,comp.1990. Impactsof forestharvestingandregenerationon forestsites.LandManagementReport67.Victoria:BritishColumbiaMinistryofForests.90p.

McNabb,D.H.;Hobbs,S.D.1989.Shallowtillagefailstoincrease5-yeargrowthofponderosapineseedlings.NorthwestScience.63:241-245.

Meek,P.1994.Acomparisonoftwoskiddersequippedwithwideandextra-widetires.FieldNoteNo.:Skidding/Forwarding-28.ForestEngineeringInstituteofCanada.48p.

Miller,R.E.;Colbert,S.R.;Morris,L.A.2004.Effectofheavyequipmentonphysicalpropertiesofsoilsandonlong-termproductivity:Areviewofliteratureandcurrentresearch.TechnicalBulletinNo.887.ResearchTrianglePark,NC:NationalCouncilforAirandStreamImprove-ment(NCASI),Inc.76p.

Stewart,R.;Froehlich,H.;Olsen,E.1988.Soilcompaction:aneconomicmodel.West.J.Appl.For.3(1):20-22.

Unger,P.W.;Cassel,D.K.1991.Tillageimplementdisturbanceeffectsonsoilpropertiesrelatedtosoilandwaterconservation:Aliteraturereview.SoilandTillageResearch.19:363-382.

Special Topic—Grand Fir Mosaic



D. E. Ferguson is a research forester, Rocky Mountain Research Station, Moscow, ID. J. L. Johnson-Maynard and P. A. McDaniel are soil scientists, Soil & Land Resources Division, University of Idaho, Moscow, ID.

Abstract TheGrandFirMosaic(GFM)ecosystemisfoundonash-capsoilsinsomemid-elevationforestsofnorthernIdahoandnortheasternOregon.HarvestingonGFMsitesresults insuccessionalplantcommunities that are dominated by bracken fern (Pteridium aquilinum) and western coneflower(Rudbeckia occidentalis),andhavelargepopulationsofpocketgophers(Thomomys talpoides).SuccessiontotreesandshrubsisveryslowondisturbedGFMsites.Fourfactorscontributetotheprotractedstagesofbrackenfernplantcommunitiesandtheslowrateofsuccessiontowoodyplants:(1)competitionamongplantsforsiteresources,(2)allelopathyfrombrackenfernandwesternconeflower,(3)pocketgopheractivity,and(4)anonallophanicsoilformingprocess.Nonallophanicsoilsoccurunderthebrackenfernsuccessionalplantcommunities—theyaredominatedbyAl-humuscomplexes,havestronglyacidpH,havehighKCl-extractableAl,andmaycauseAltoxicitytoplants.Allophanicsoilsoccurunderforestedconditions—theyaredominatedbyallophaneandimogolite,haveweaklytomoderatelyacidpH,andhavelowAlavailability.Allophanicandnonallophanicsoilsexistside-by-sideintheGFM,withmineralogybeingdependentuponthedominantvegetation.Brackenfernandwesternconeflower,withbelow-groundcarboninputsfromtheirwell-developedrootsystems,provideamechanismthatpromotestheshiftfromallophanictononallophanicsoils.RecommendationsforreforestingGFMsitesareprovided.

The Grand Fir Mosaic Ecosystem—History and Management Impacts

D. E. Ferguson, J. L. Johnson-Maynard, P. A. McDaniel

Introduction

ImagineamoistforestenvironmentinthenorthernRockyMountainswheresupposedlyseralplantcommunitiesdominatedbybrackenfern(Pteridium aquilinum)andwesternconeflower(Rudbeckia occidentalis)arereallyclimaxplantcommunitiesthatpersistwithinamatrixofovermaturegrandfir(Abies grandis)andwesternredcedar(Thuja plicata)forests.Therearefewwildfireshere,sonaturalsuccessionhasreducedtheoccurrenceofseralconiferssuchaslodgepolepine(Pinus contorta),Douglas-fir(Pseudotsuga menziesii),westernwhitepine(Pinus monticola),andwesternlarch(Larix occidentalis).Latesuccessional,shade-tolerantspe-cieslikegrandfir,westernredcedar,Pacificyew(Taxus brevifolia),andsometimesmountain


Ferguson, Johnson-Maynard, and McDaniel The Grand Fir Mosaic Ecosystem—History and Management Imacts

hemlock(Tsuga mertensiana)andsubalpinefir(Abies lasiocarpa),arecommonalongwithmid-successionalEngelmannspruce(Picea engelmannii).RegenerationofconifersinforestcanopyopeningsisaslowandunreliableprocessintheselowpHvolcanicash-capsoilsthathaveabundantpopulationsofpocketgophers(Thomomys talpoides).Disjunctandrareplantspeciesoccurinandneartheseforests, including evergreen synthyris (Synthyris platycarpa), Oregon bluebell(Mertensia bella),Dasynotus(Dasynotus daubenmirei),andCase’scorydalis(Co-rydalis caseana).ThesemoistforestsarecollectivelycalledtheGrandFirMosaic(GFM)ecosystem.

GrandFirMosaicforestsoccuronproductivevolcanicash-capsoilsinandneartheClearwater,NezPerce,andsouthernSt.JoeNationalForestsinnorthernIdaho,andtheUmatillaNationalForestinnortheasternOregon.ThenamefortheGFMcomesfromthedominantconifer(grandfir)andthevarietyofsizesandshapesofnaturalopeningsintheforestcanopy.TheGFMencompassesapproximately500,000acresatelevationsprimarilybetween4,500and5,500ft,butisfoundaslowas4,200ftandashighas6,000ft(FergusonandJohnson1996).ThemostcommonhabitattypeisAbies grandis/Asarum caudatum(grandfir/wildginger),acool,moisthabitatdefinedbyCooperandothers(1991).

SuccessionalplantcommunitiesintheGFMaredominatedbybrackenfernandwesternconeflower.Brackenfernisusuallypresentinlowdensitiesunderforestcanopies,butrapidlyexpandsfollowingdisturbance,andcanreachheightsof6ftanddensitiesof116,000frondsperacre(Znerold1979).Below-groundbrackenbiomass,primarilyrhizomesandfineroots,maybeasmuchas27,280lbsperacre(Jimenez2005).

Bracken ferngladesareplant communitiesdominatedbybracken fernandwesternconeflowerthatappeartopersistformillennia.CharcoalsamplesfoundatornearthelowerboundaryofGFMash-capswerefoundtobe1,335±75and7,755±75cal.yrsBPusingradiocarbondating(Jimenez2005).Thesecharcoalsamplessuggestthatwoodyvegetationhasbeenabsentforthousandsofyears,perhapsdatingback to the timeof ashdepositionduring theeruptionofMt.Mazama(CraterLake,OR)~7,600yrsBP(Zdanowiczandothers1999).

Pocket gophers also alter the course of secondary succession in the GFM,particularlyforplantedconifers.Entireplantationsofseedlingscanbekilledbypocketgophers.Smallseedlingsareusuallypulledfrombelowgroundintotunnelswherethewholetreeiseaten.Gophersmayeatallormostoftherootsystemoflargerseedlingsandsaplings.

OurinvestigationsontheGFMwereinitiatedbecauseofdifficultyinregen-eratingharvestedareasintheGFM.Thefirsttaskwastodefinekeyecologicalprocessesthatmightaccountforthelackofregenerationandtheabsenceofotherwoodyspecies.Researchwasplannedandimplementedtostudycompetitionand allelopathy from bracken fern and western coneflower, effects of pocketgophers,environmentalcharacteristicsof theGFMrelative toadjacent forests,andsoildevelopment.

Bracken Fern, Western Coneflower, Pocket Gopher, and Environmental Research

There isabundant researchonbracken fern fromaround theworlddealingwithallelopathy,competition,encroachmentrates,andharmtocrops,livestock,


The Grand Fir Mosaic Ecosystem—History and Management Impacts Ferguson, Johnson-Maynard, and McDaniel

andhumans.Theallelopathicpotentialofbrackenfernhasbeendemonstratedbyseveralresearchers,includingStewart(1975)andGliessman(1976).TheallelopathicpotentialofbrackenfernintheGFMwasdemonstratedbyFergusonandBoyd(1988),whofoundthatmostoftheseedsthatgerminatedonsoildominatedbybrackenferndiedbeforetheseedcoatwasshed.Ferguson(1991)demonstratedallelopathicpotential forwesternconeflowerinlaboratorytests.Volatilecom-pounds(vapors)fromwesternconeflowerreducedordelayedseedgermination,andwaterextractsreducedgrowthoftheseedlingradicle.

GrowthandmortalityofplantedconifersatGFMsiteswasreportedbyFergusonand Adams (1994) and Ferguson (1999). Hand weeding of bracken fern andwesternconeflowerfromplantingsitesincreasedheightgrowthofplantedconiferseedlings.Pocketgopherskilledfrom24to59percentoftheseedlings,dependingonspecies.Oftheseedlingskilledbypocketgophers,77percentwerekilledthefirstsummer(followingspringplanting)andthefirstorsecondwinter,butfewseedlingswerekilledthesecondorthirdsummers.

EnvironmentalconditionswerestudiedbyFergusonandByrne(2000)toseeiftheydifferedbetweenGFMandnon-GFMsitesinthesamevicinity.RemotemonitoringstationswereusedtosampleharvestedareasataGFMsiteandthreeadjacenthabitattypes(non-GFMgrandfir,subalpinefir,andwesternredcedar).Variablessampledwerewindspeedandwinddirectionat9 ftabove thesoilsurface;precipitation;solarradiation;relativehumidityat4.5ft;airtemperatureat4.5ft;soiltemperatureonthesoilsurface,1inch,and8inchesdepth;soilwaterpotentialat1inchand8inches;andsoilpHat1inch.

Comparisonof theGFMsite tonon-GFMsites in thesamevicinityshowedthattheGFMsitehadashortergrowingseason,eventhoughoneofthesiteswasasubalpinefirhabitattype140fthigherinelevationthantheGFMsite.SnowmeltedattheGFMsiteanaverageof9dayslaterthanatthesubalpinefirhabitattype,24dayslaterthanatthenon-GFMgrandfirhabitattype,and52dayslaterthanatthewesternredcedarhabitattype.

AverageGFMsoiltemperaturesat1and8incheswerecoolerthanthenon-GFMsitesinAprilandMaybecauseoflatesnowpacksattheGFMsite.Duringtherestofthegrowingseason,theGFMsitewaswarmerthanthesubalpinefirhabitattype,butcoolerthanthegrandfirandwesternredcedarhabitattypes.

Summersoilmoistureat theGFMsitedidnotdrytothepermanentwiltingpointasoftenasthenon-GFMsites.Soilsat8inchesdriedtoawaterpotentialof–15barsinonly2of6yearsofmonitoringattheGFMsite,while–15barswasreachedduring4ofthe6monitoringyearsatthenon-GFMgrandfirhabitattype,4of5yearsatthewesternredcedarhabitattype,and5of5yearsatthesubalpinefirhabitattype.

ThemostinsightfulvariablemeasuredwassoilpHat1-inchdepth.TheGFMsitewasdifferentfromtheotherthreesitesbecausesoilpHcycledfromabout6.0inthespringto4.0inthesummerandbackto6.0inthefall(fig.1).Eachyearfor7years,soilpHwaslowerthan5.0forseveralweekstoafewmonths.AsoilpHbelow5.0isacommonlycitedthresholdwhereAltoxicityiscom-montomanycrops(Shojiandothers1993).AlaboratorystudyhasshownthatexchangeableAlincreasesexponentiallyinGFMsoilsaspHdecreasesbelow5.0(Page-Dumroeseandothers,thisproceedings).



Ash-cap Soil Relationships _______________________________________

Allophanic and Nonallophanic Andisols

The Andisol soil order includes soils that are characterized by andic soilpropertiesthatarisefromthepresenceofsignificantamountsofnoncrystallinealuminosilicatessuchasallophaneandimogolite,Al-humuscomplexes,and/orpoorlycrystallineFeoxides(SoilSurveyStaff2003).AlackofilluvialBhorizonsindicates that theprocessof translocation isnotsignificantwithin theAndisolorder(Ugoliniandothers1988;Dahlgrenandothers1991)andclearlyseparatesAndisolsfromothersoilorderswithsimilarmineralogicalcomponents.

Andisolsarecommonlydescribedasbeingallophanicornonallophanic,de-pendingonthenatureofthemineralspresent.AllophanicAndisolsaredominatedbyallophane,imogolite,andclayminerals;areweaklytomoderatelyacid;andhavelowKCl-extractableAlandlowAlsaturation(table1)(Shojiandothers1985;Nanzyoandothers1993).NonallophanicAndisolshaveAl-humuscomplexesandcrystallineclaymineralsastheirdominantmineralogicalcomponents,andcontain

Figure 1—Average daily soil pH at 1 inch for a GFM site, 19�9 through 199� (Ferguson and Byrne 2000). Each line is a different year of data, and discontinuous lines are periods of time when soils were too dry to collect pH measurements. The horizontal line at pH � shows a commonly cited threshold where plants start to experience Al toxicity.

Table 1—Comparative characteristics of allophanic and nonallophanic Andisols.

Characteristic Allophanic NonallophanicMineralogy More allophane and imogolite; Less allophane and imogolite: less Al-humus complexes more Al-humus complexes

Soil acidity Weakly to moderately acid Strongly acid

Exchangeable Al Low High

Al toxicity Rare Common



asubstantiallysmallerproportionofallophaneandimogoliteascomparedtoal-lophanicAndisols.Inaddition,nonallophanicsoilsarestronglytoverystronglyacid,havehighKCl-extractableAl,andcommonlyexhibitAl toxicity (table1)(Shoji and others 1985; Nanzyo and others 1993). Al-humus complexes andhighconcentrationsofexchangeableAlinnonallophanicAndisolsresultinrapiddissolutionandequilibriumbetweenAlinsolidandsolutionphases.AllophanicAndisolsaredominatedbyallophaneandimogolite,whichhaveslowerdissolu-tionratesand,therefore,resultinslowerreleaseofAlintosoilsolution(DahlgrenandSaigusa1994;Dahlgrenandothers2004).TherapidreleaseratesofAlinnonallophanicAndisolsprovideasourceofAlforplantuptake.Duetothepos-sibilityofAltoxicity,thedistinctionofallophanicandnonallophanicAndisolsisimportantformanagementpurposes.

BecauseoftheimpactofAndisolmineralogyonplantproductivity(Dahlgrenandothers2004),itisimportanttounderstandthefactorsthatcontrolmineralformationandweatheringwithintheorder.Differencesinparentmaterialsuchas tephraage,geochemistry,hydraulicproperties,andadditionsofexogenousmaterialssuchasloess(InoueandNaruse1987;Vaccaandothers2003)havebeenreportedtoinfluencethedevelopmentofcertainmineralogicalcomponentswithinash-influencedsoils.Otherfactorsthataremoreinfluencedbymanage-mentincludeorganicmatterandpH(ShojiandFugiwara1984;Johnson-Maynardandothers1997).TheformationofallophanicAndisolstendstobefavoredinenvironmentswherepHisgreaterthan5.Incontrast,nonallophanicAndisolsarepredominatelyfoundinmoreacidic(pH<5)environmentswithhigherconcentra-tionsoforganicmatter(ShojiandFujiwara1984;Shojiandothers1993).

Therelationshipbetweenorganicmatter,pH,andAlavailabilityindicatesthatplantcommunitiesmayplaya role in influencingAndisolproperties. Specificexamples of the impact of vegetation and vegetation conversion on Andisolmorphologyandchemistryhavebeenreported.Japanesepampasgrass(Miscan-thus sinensis),forexample,isassociatedwiththeformationofdark,humus-rich,surfacehorizonsknownasmelanicepipedons(Shojiandothers1990).BiomassproductionbyJapanesepampasgrasswasestimatedtobe4,840lbsperacreabovegroundand15,500lbsperacrebelowground.Withalloftheabove-groundandone-quarterofthebelow-groundpartsaddedtothesoileachyear,Japanesepam-pasgrasscreatesconditionsthatpromoteaccumulationandhumificationofsoilorganicmatterresultingintheformationofmelanicepipedons(Shojiandothers1993).Dahlgrenandothers(1991)reportedloweringofsoilsolutionpHwithacorrespondingincreaseinAlconcentrationsinAhorizonsofAlicMelanudandswhereJapaneseoak(Quercus serrata)replacedJapanesepampasgrass.Theac-cumulationoforganicmatterwasadistinguishingfeaturebetweensoilsunderthetwovegetationtypes.AnotherexampleoftheeffectofplantsonAndisolscanbefoundontheNorthIslandofNewZealandwhereAndisolsrarelydisplaythickdarkhumushorizonsexceptwherenativepodocarpforesthasbeenconvertedtobrackenfern(Pteridium aquilinum var. esculentum)(Leamyandothers1980).

Andisols in the Grand Fir Mosaic

Sommer (1991) sampled soilsand foliage in threeGFMplantcommunities:matureforest,naturalbrackenfernglade,andbracken-invadedclearcut.SoilpHwaslowerandexchangeableAlwashigherinbracken-dominatedplantcommuni-tiesthaninthematureforest.Soilandfoliarnutrientswereadequateforconifer



growth,althoughAlwasapproaching levelsknown tobe toxic tosomeplantspecies.Smallsamplesizeandhighvariabilitypreventedconclusiveresults,butevidencesuggestedthatdisturbedforestsitesintheGFMareinvadedbybrackenfernplantcommunitiesandbecomemorelikebrackenfernglades.

TheimportantdocumentationofbothallophanicandnonallophanicAndisolsin theGFMwasreportedby Johnson-Maynardandothers (1997).Soilchemi-calandmineralogicalpropertieswerestudiedinadjacentmatureforest,naturalbrackenfernglade,andbracken-invadedclearcut.Retrospectivecomparisonofthe30-year-oldclearcuttothematureforestandbrackenferngladeshowedaconversionfromallophanictononallophanicsoils(fig.2).Soilsintheforestweredominatedbyshort-range-orderAl-Feminerals,hadlowexchangeableAl,andhadpH>5,allofwhichareconsistentwithcharacteristicsofallophanicsoils(table1).Soilsinthebracken-invadedclearcutandbrackenferngladeweredominatedbyAl-humuscomplexes,hadhighexchangeableAl,andpH<5,whichisconsistentwithnonallophanicsoils. Johnson-Maynardandothers (1997)werethefirst toreportnonallophanicAndisolsinnorthernIdaho.Also,theywerethefirst,toourknowledge,toreportaconversionfromallophanictononallophanicmineralogy.Allophanicandnonallophanicsoilsexistside-by-sideintheGFM,theirexpressionbeingdependentuponthedominantplantcommunity.

ThechemistryofsoilwatermovingthroughsoilsoftheGFMhasalsobeenstudiedintheGFM(Johnson-Maynardandothers1998),usingthesamestudysitesasJohnson-Maynardandothers(1997).SoilwaterchemistrywasconsistentwiththepreferentialformationofAl-humuscomplexesinbracken-dominatedsitesthathadoncebeenforested.Soilsolutionwasalsocollectedfromaweededareainabrackenferngladewherebrackenfernandwesternconeflowerwerehandweededfor6yearspriortosampling(Ferguson1999).SoilwaterpH,Al,anddissolvedorganiccarbonintheweededareaweremoresimilartotheforestthantosoilwatercollectedfromunderthebrackenfernglade.Weedingappearedtoresultinsoilwaterwithchemicalcompositionmoresimilartothatmeasuredin

Figure 2—Depth distribution of Al in soil fractions as determined by selective dissolution techniques (adapted from Johnson-Maynard 199�).



theundisturbedforest,suggestingthatthegrowthofbrackenfernandwesternconeflowerplayanimportantroleintheconversionfromallophanictononal-lophanicsoils.

AlthoughsoilwaterAlconcentrationswerehighestinbracken-dominatedplantcommunities, theywere lower thanpublished toxicity levels forother coniferspecies.MoreworkisindicatedtodeterminetoxiclevelsforplantspeciesintheGFMandtodeterminethedifferentformsandtoxicityofAlinsoilsolution.

Discussion ______________________________________________________ResearchontheGFMecosystemhasidentifiedfourfactorsthat,individually

andcollectively,mayaccountfortheslowrateofsecondarysuccessiontowoodyvegetationfollowingdisturbancesthatcreateopeningsintheforestcanopy.Thefirst factor iscompetitionamongplants forsite resourcessuchas light,water,nutrients,andgrowingspace.Competitioncanbeintensebecauseforbcommu-nitiesdominatedbybrackenfernandwesternconeflowerexpandrapidly intopreviouslyforestedopenings.

The second factor is allelopathy. Direct and indirect effects of phytotoxinsreleasedbyplantscanreducethesuccessfulestablishmentandgrowthofotherspecies.Theallelopathicpotentialofbrackenfernandwesternconeflowerhasbeendemonstrated(Stewart1975;Gliessman1976;Ferguson1991).Thequantificationof the individualeffectsattributable toallelopathyandcompetition isdifficultbecauseremovalofaplantfromitsnaturalenvironmentsimultaneouslyremovesthesourceofallelopathyandcompetition.Ecologistsusetheterm“interference”torefertothecombinedeffectsofallelopathyandcompetition(Muller1969).

The third factor is largepopulationsofpocketgophers.GopherscancauseasubstantialamountofmortalitytoplantedandnaturalseedlingsintheGFM.Mostgopher-causedmortalitytoplantedseedlingstakesplacethefirstsummerafterplantingandduringthefirstandsecondwinters(Ferguson1999;Fergusonandothers2005).Partialremovaloftheoverstorycanopyallowsenoughlighttoreachplantedseedlingssotheycansurviveandgrow—albeitslowerthaninfullsunlight—andalsoreducesabundanceofpocketgophers,brackenfern,andwesternconeflower(Fergusonandothers2005).

Thefourthfactorisanonallophanicsoilformingprocess.ThedatacollectedbyJohnson-Maynardandothers(1997,1998)demonstratetheconversionofal-lophanictononallophanicmineralogybasedonthecriteriasummarizedintable1.Intheundisturbedforest,thedominantsecondarymineralogicalcomponentofsoilsisinorganic,short-rangeorderminerals,whichisconsistentwithallophanictypeAndisols.Inbracken/coneflowerdominatedareas,Al-humuscomplexesarethedominantcomponentofsoils,consistentwithwhathasbeendescribedinnonallophanicsoils.

Allophanicandnonallophanicsoilsexistside-by-sideintheGFM,withmineral-ogydependentuponthedominantvegetation(fig.2).Allophanicconditionsoccurwhenvegetationisdominatedbyconiferoustrees,butnonallophanicconditionsoccurwhensitesaredominatedbybrackenfernandwesternconeflower(John-son-Maynardandothers1997).Whenbrackenfernandwesternconeflowerareremoved,soilwaterchemistryissimilartothatunderallophanicGFMsoils(Johnson-Maynardandothers1998),indicatingthatbrackenfernandwesternconeflowerareamechanisminpromotingnonallophanicsoils.Itislikelythatbrackenfernandwesternconeflowerarenotonlysourcesoflargeannualadditionsofcarbon



tothesoil,thusfavoringtheformationofAl-humuscomplexes,butalsosourcesoforganicacidsthatlowersoilpH(Johnson-Maynardandothers1998).

Reforesting GFM Sites____________________________________________Inthissection,wediscussmanagementstrategiesforreforestingGFMsitesas

theyrelatetothenonallophanicsoilformingprocess.ThemostimportantpointtorememberisthatnaturalregenerationofwoodyplantspecieswillbeaslowandunreliableprocesswithintheGFM.WeknowofmanyexamplesofcutoverGFMforeststhathavelittlewoodyvegetationafter20to30years.Seedsthatgerminateinopenings in theGFMforestcanopyaresubject tocompetition,allelopathy,pocketgophers,andAltoxicity.Thesefourfactorscancombinetovirtuallyelimi-natethenaturalestablishmentoftreesandotherwoodyplantspecies.

Promptplanting followingadisturbancewill help seedlingsbecomeestab-lishedbeforethesitehasabundantbrackenfern,westernconeflower,andpocketgophers.Plantinglargervs.smallerseedlingshelpsincreasesurvivalandgrowthrates.Plantedseedlingsinclearcutsneedtobeprotectedfrompocketgophersuntilthethirdspringaftertheyareplanted.

Partialcuttings,whereonlyaportionoftheoverstorytreesareremoved,re-taintheshrubcomponentbetterthanclearcuts,andresultinlessbrackenfern,westernconeflower,andgopher-causeddamagetoseedlings(Fergusonandoth-ers2005).Plantedtreesdonotneedprotectionfrompocketgophersinpartialcuttings;however,theywillnotgrowasfastasinclearcuts.Afterseedlingsareestablished(5to10years),allorpartof theremainingoverstorytreescanberemovedtoimprovegrowthofseedlings.

Theoverallperformanceofsomeplantedconiferspecieswasbetter in trialplantingsonGFMsites(Ferguson1999;Fergusonandothers2005).Engelmannspruceandwesternwhitepinegrewwell,hadlittlemortalityfromnon-gophercauses,andhadlittletopdamagefromsnoworsenescingbrackenfernfronds.Douglas-firalsodidquitewell,especiallyiflargerseedlingswereplanted.Lodge-polepinegrewrapidly,butthisspeciesoftensufferedseveresnowdamagetotops,limbs,andstems.Westernlarchhadveryhighoverallmortality,bothfromgopherandnon-gophercauses,butsurvivingtreesgrewrapidly.AnotherconcernwithwesternlarchistopdamageandsevereleancausedbysnowloadsintheGFM.

Research Questions _____________________________________________Muchhasbeenlearnedaboutash-capsoilsandmanagementoptionsforthe

GFM,andadditionalresearchwouldhelpfillthegapsinourknowledge.Researchstudiesshowthatallophanicandnonallophanicsoilformingprocessesexistside-by-sideintheGFM.Allophanicprocessesoccurwhereconifersdominatethesite,andnonallophanicprocessesoccurwherebrackenfernandwesternconeflowerdominate.Itwouldbehelpfultostudyallophanicvs.nonallophanicmineralogyacross a range of overstory densities, and determine how quickly allophanicprocessesturnintononallophanicprocessesfollowingharvestorotheractivitiesthatreducethedensityoftheforestcanopy.

Anotherkey research topic is tounderstandwhypHiscyclic inGFMsitesdominatedbybracken/coneflowersuccessionalplantcommunities(fig.1).Com-parisonsofseasonalpatternsinpHunderbrackenferngladestoundisturbedgrandfirforestsmayshedlightonthemechanismsbehindthisobservation.



SoilpHvaluescyclebelow5.0duringpartofthegrowingseason,whichcouldresult in Al toxicity (Page-Dumroese and others, this proceedings). However,littleisknownaboutAltoxicitythresholdsforplantspeciesandtheirmychor-rhizalassociationsintheGFM.WewouldexpectthatAltoxicityvarieswithAlconcentration,thevariousAlcompoundsthatexistinash-capsoils,andsize/ageofplantspecies.ThecyclicnatureofsoilpHintheGFMmayalsointerferewithnutrientavailability(seePage-Dumroeseandothers,theseproceedings).Moreinformation isneededonavailabilityofnutrientsother thanAl, especiallyni-trogen.RecentworkhassuggestedthatadditionsoflimeareeffectiveinraisingpHandreducinglevelsofbioavailableAlinnonallophanicAndisols(Takahashiandothers2006).Limingexperimentscouldthereforebeusedtoprovidevalu-ableinformationabouttheroleofpHandactiveformsofAlintreeregenerationproblemsobservedintheGFM.

Theallelopathicpotentialofbrackenfernhasbeendemonstratedbyseveralresearchersaroundtheworld,butweonlyhaverudimentaryknowledgeofal-lelopathyinwesternconeflower.Ferguson(1991)demonstratedtheallelopathicpotential ofwestern coneflower in laboratory tests, but additional research isneededunderfieldconditions.

TheanswerstotheseresearchquestionswouldimproveourknowledgeofthemechanismsthatdelaysecondarysuccessiontowoodyplantspeciesintheGFM,therebyhelpingrefinemanagementrecommendationsforGFMash-capsoils.

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Deborah Page-Dumroese and Dennis Ferguson are Research Scientists at the Rocky Mountain Research Station, U.S. Forest Service in Moscow, ID; Paul McDaniel and Jodi Johnson-Maynard are faculty in the Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow, ID.

Abstract Datafromvolcanicash-influencedsoilsindicatesthatsoilpHmaychangebyasmuchas3unitsdur-ingayear.Theeffectsofthesechangesonsoilchemicalpropertiesarenotwellunderstood.OurstudyexaminedsoilchemicalchangesafterartificiallyalteringsoilpHofash-influencedsoilsinalaboratory.Soilfromthesurface(0-5cm)andsubsurface(10-15cm)mineralhorizonswerecollectedfromtwoNationalForestsinnorthernIdaho.Soilcollectionsweremadefromtwoundisturbedforeststands,apartialcut,anaturalbrackenfern(Pteridium aquilinum[L.]Kuhn)glade,anapproximately30-year-oldclearcutinvadedwithbrackenfern,anda21-year-oldclearcutinvadedwithwesternconeflower(Rudbeckia occidentalisNutt.).Eitherelementalsulfur(S)orcalciumhydroxide(Ca(OH)2)wereaddedtothesoiltomanipulatepH.After90daysofincubation,pHrangedfrom3.6to6.1forbothNationalForestsandallstandconditions.TotalC,totalN,andextractablebasecations(Ca,Mg,andK)weregenerallyunaffectedbypHchange.AvailablePincreasedaspHdroppedbelow4.5forbothdepthsandallsoiltypes.NitratewashighestatpHvaluesgreaterthan5.0anddecreasedaspHdecreasedindicatingthatnitrificationisinhibitedatlowerpH.Contrarytonitrate,potentiallymineralizableNincreasedaspHdeclined.TotalacidityandexchangeablealuminumincreasedexponentiallyaspHdecreased,especially intheuncutandpartialcutstands. Datafromthis laboratorystudyprovidesinformationontheroleofpHindeterminingtheavailabilityofnutrientsinash-capsoils.

Chemical Changes Induced by pH Manipulations of Volcanic

Ash-Influenced SoilsDeborah Page-Dumroese, Dennis Ferguson, Paul McDaniel, and

Jodi Johnson-Maynard

Introduction

Innorth-centralIdaho,someforestsarecharacterizedbyconiferregenerationproblemsdespitefavorableclimaticconditions(udicmoistureandfrigidsoiltemperatureregimes).Foreststandsatmid-elevationsaremostatriskaftertimberharvestorotherdisturbancebecausetheyarequicklyinvadedbybrackenfern(Pteridium aquilinum[L.]Kuhn),westernconeflower(Rudbeckia occidentalisNutt.),andpocketgophers(Thomomys talpoides).ThesesitesarecollectivelyknownastheGrandFirMosaic(GFM)andarenamedforthedominantconifer,grandfir(Abies grandis[Dougl.exD.Don]Lindl.),thatoccursinamosaicpatternwithshrubandforbcommunities(Ferguson1991a;Fergusonandothers,thisproceedings).


Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils

TimberharvestingbeganintheGFMinthe1960sanditsoonbecameevidentthatregenerationproblemsexisted.Woodyvegetationisstillinfrequentonmanyofthesesites30yearsafterclearcutting,evenwithrepeatedplantings(FergusonandAdams1994).Clearcutstandswerequicklyinvadedbyforbs(predominatelybrackenfernandwesternconeflower)androdents.Theallelopathicpotentialofbothbrackenfernandwesternconeflowerhasbeenwelldocumented(Stewart1975;FergusonandBoyd1988;Ferguson1991b).Inadditiontoinvadingforbs,pocketgophersalsocausesubstantialseedlingmortality (Fergusonandothers2005).Competition for light,moisture, andnutrientswithin theGFM ishigh.Whilethecombinationofcompetition,pocketgophers,andallelopathycontributetothearrestedstateofsecondarysuccession(FergusonandAdams1994),thesefactorsdonotappeartoentirelyexplainreforestationfailures.

Soils throughout the GFM are strongly influenced by volcanic ash in thesurfacehorizons.Theashwasdepositedapproximately7,700yearsagowhenMt.Mazama erupted (Zdanowicz 1999). Volcanic ash-influenced soils haveuniqueparentmaterialsandsecondarymineralassemblagesthat,ingeneral,arenotaswellunderstoodasthoseinothermineralsoils.Volcanicash-influencedsoilsareclassifiedaseitherallophanicornonallophanic,dependingontherela-tiveabundanceoforganicmatterandinorganicshort-range-orderminerals(Shojiand others 1993). Nonallophanic soils have more organic matter, lower pH,higherlevelsofKCl-extractablealuminum(Al),andlowerlevelsofcalcium(Ca)relative toallophanicsoils (Shojiandothers1993).LowsoilpHmay increaseconcentrationsofextractable(potentiallyplantavailable)Al,leadingtoAltoxic-itytowoodyvegetation(Dahlgrenandothers1991).Clearcuttingandintensiveutilization(wholetreeharvesting)offorestbiomassmayacceleratesoilacidifica-tionprocesses(Ulrichandothers1980;NoskoandKershaw1992).Inadditiontoacidificationfromharvestactivities,vegetation-inducedacidificationappearstooccurunderbrackenfernandwesternconeflowerplantcommunities(Johnson-Maynardandothers1997).Theseacidifiedvolcanicash-influencedsoils,whicharehighinexchangeableAl,mayreleaseAlintosoilsolutionatlevelstoxictowoodyvegetation(AndereggandNaylor1988).

Twosoil factorshavebecomeaconcerninGFMforestopenings.First,soilpH drops below 5.0 after harvest operations and the subsequent invasion ofbrackenfernandwesternconeflower(figs.1and2).AtthispH,AlcanreachtoxiclevelsandlowsoilpHcaninhibitgrowthofsomeseedlingspecies(NoskoandKershaw1992).Second,thereareseasonalpHfluctuationsof2-3pHunitsthatarenottypicallyfoundinbulkmineralsoilunlessheavilyimpactedbyacidrainor,occasionally,harvestactivities(Mrozandothers1985;Braisandothers1995;Alewellandothers1997).WinterpHvaluesaveragearound6,butdropbelow4duringthegrowingseason.TheseseasonalpHfluxescouldbecorrelatedwithinputsofacidlitterfrombrackenfernandwesternconeflower,increasingrootrespirationduringthegrowingseason,ordecreasesinsoilmoisturecontent.Inaddition,thesetwospecieslikelytakeuphighamountsofnutrientsfromthesoil,whichmayalsocontributetoacidconditions(Gilliam1991).ManyfactorsinfluenceforestsoilpH(forexample,precipitation,nutrientexchange,andsoilage),butharvestactivitycanparticularlyinfluenceit (StaafandOlsson1991).AlthoughforestharvestingcanlowerpH,subsequentinvasionbybrackenfernandwesternconeflowerappearstocontributetoandmaintainlowpHrelativetoundisturbedforestsoils.


Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard

Figure 2—Average soil pH at 2.� cm for the Clearwater National Forest fern-invaded clearcut (unpublished data collected as described in Ferguson and Byrne 2000). The bold line is 1997 and the thin line is 199�.

Figure 1—Average soil pH at 2.� cm for the Nez Perce National Forest coneflower-invaded clearcut (from Ferguson and Byrne 2000). The bold line is 1994, which was a dry growing season. The thin line is 199�, which was a wet growing season. Dis-continuous parts of the line are from removal of the pH probe during the driest part of the growing season. Soil pH at this site was assessed in situ using pH probes (model �1�, IC controls Orangeville, Ontario, Canada) buried 2.� cm below the mineral soil surface.



TheslowforestregenerationprocessintheGFMhasdecreasedmanagementoptionsforfuelreductionsandbiomassproduction,biodiversityofnativefloraandfauna,andaestheticvaluesinandneartheseareas.LowsoilpHanditscyclicnatureover a growing seasonmaybealtering soil chemistry, nutrient cyclingprocesses, and preventing establishment of woody vegetation. Consequently,ourobjectivewastoartificiallyalterpHofash-influencedforestsoilsfromtheGFMbyadditionsofsulfur(S)orcalciumhydroxide(Ca(OH)2)tobetterevaluatepotentialin situ chemicalchangeswithinthesesoils.

Study Site Description ___________________________________________Twostudysites,oneontheClearwaterNationalForestandoneontheNez

PerceNationalForestofnorth-centralIdaho,wereselectedtoprovideanorth/southrangeofplantcommunitycovertypesforsoilcollection.TherearethickerdepositsofvolcanicashinthenorthernpartoftheGFMwherethesesoilsareclassifiedasAndisols.InceptisolsdominateinthesouthernpartoftheGFMwhereashdepositsare thinnerandmorehighlymixed.Bracken ferndominates forbcommunitiesinthenorthernpartoftheGFMandwesternconeflowerdominatesinthesouthernpart,althoughbothspeciesoccurtogetherthroughouttheGFM.Table1listsstudysitelocations,vegetationtypes,andsoilclassifications.

ClearwaterNational Forest soil sampleswere collected in 1994near EaglePoint(elevation1,400m,easternaspect,20percentslope,T40N,R7E,S35).Thedominantsoilfeatureofthisstudyareaisapproximately60cmofMt.Mazamavolcanic ashunderlainwith colluviumor residuumderived from fine-grainedigneousrock.Toassesstheimportanceofvegetationcommunitystructure,soilsampleswerecollectedfromadjacentareaswithsimilarslope,aspect,andpar-entmaterial, butdifferent vegetationcover. Soil sampleswere collected fromtheundisturbed forest (46m2ha–1basal areaofoverstory), apartial cut (ap-proximately30m2ha–1ofoverstoryremaining),anaturallyoccurringbrackenfernglade(presentwhentheadjacentareaswereharvested),anda~30-year-oldbrackenfern-invadedclearcut(invadedbybrackenfernandwesternconeflowerafterharvestingbetween1965and1968).

NezPerceNationalForestsoilsampleswerecollectedin1994atDogleg(eleva-tion1,740m,southernaspect,5percentslope,T31N,R6E,S34).Thedominantsoilfeatureisapproximately40cmofMt.Mazamavolcanicashunderlainwithdeeplyweatheredmicaschist(Sommer1991).Vegetationtypesatthissitewereundisturbedforest(45m2ha–1basalareaofoverstory)anda21-year-oldwestern

Table 1—Location, vegetation type, and soil classification of study sites.

National Forest Vegetation type Soil classification‡

Clearwater Undisturbed forest Typic HapludandNez Perce Undisturbed forest Vitrandic CryumbreptClearwater Partial cut Typic HapludandClearwater Natural bracken fern glade Alic FulvudandClearwater �0-year-old bracken fern-invaded clearcut Alic HapludandNez Perce 21-year-old western coneflower-invaded clearcut Vitrandic Cryumbrept‡ Clearwater National Forest soil classifications from Johnson-Maynard and others (1997)Nez Perce National Forest soil classifications from Sommer (1991).



coneflower-invadedclearcut(invadedbywesternconeflowerandbrackenfernafterharvestingin1973).Vegetationtypeswereadjacenttoeachother,havingsimilarslope,aspect,andparentmaterial.Therewerenonaturalwesternconeflowergladesdatingtopre-harvestactivitiesandnopartialcutstandsinthevicinity.

Methods _______________________________________________________

Field Collection Methods

Ineachforestandvegetationtype,mineralsoilwascollectedfromthe0-5cmand10-15cmdepths.Soilsampleswerebrought to theUSDAForestService,MoscowLaboratory,airdried,andpassedthrougha2-mmsieve.InitialpHwasmeasuredelectrometricallyina2:1water:soilsuspension.

Laboratory Methods

DependingoninitialsoilpH,wechosefivetreatmentstoraiseorlowersoilpHinanattempttoestablisharangeofpHvaluesfrom3.5to6.0.Foreachvegeta-tiontypeanddepth,Satratesof0.45,0.90,1.80,2.70,or3.6gkg–1orCa(OH)2atratesof0.45,0.90,or1.80gkg –1wereaddedtoprovidearangeofpHvalues.Inaddition,therewasacontrol(nochemicaladded)foreachvegetationtypeandsoildepth.EachSorCa(OH)2soiladditionrateandthecontrolfromeachvegetationtypewasreplicatedthreetimes.Soilwasplacedin655cm3plastictubeswithnylonscreenoverthebottomopeningstopreventsoilloss.

Soilwaterpotentialwasbroughtto–0.033MPabytheadditionofdeionizedwater.Thetubeswererandomlylocatedonagreenhousebenchandincubatedatadaytimetemperatureof25°Candanighttimetemperatureof18to20°CuntilthepHstabilized(90days).Whensoilwaterpotentialdroppedbelow–0.10MPa,additionaldeionizedwaterwasaddeduntilthesoilreachedfieldcapacity.AfterpHstabilized(unchangedfor5days),soilwasairdriedforchemicalanalyses.FinalpHwasmeasuredasdescribedaboveaftertheincubationperiod.

Totalcarbon(C)andnitrogen(N)wereanalyzedinaLECOinductionfurnaceoperatedat1050°C(LECOCorp,St.Joseph,MI).Totalacidityandexchange-ableAlwereextractedwith1NKCl (BertschandBloom1986).Exchangeablecalcium(Ca),magnesium(Mg),andpotassium(K)wereextractedusing1NNH4Cl(Palmerandothers2001).CalciumandMgwereanalyzedbyatomicabsorptionspectroscopy,andKwasanalyzedbyflameemission.Nitrate-N(NO3-N)wasdeterminedonmoistsamplesusing1NKClextractandanAlpkemRapidFlowAnalyzer(Mulvaney1996).PotentiallymineralizableN(PMN)wasestimatedus-ingthe7-dayanaerobicincubationtechniqueonmoistsamples(Powers1980).Extractablephosphorus(P)wasdeterminedusingeithertheBray1method(forsampleswithapH<6.0)ortheOlsenmethod(forsampleswithapH>6.0)(Kuo1996).Organicmatterwasdeterminedbyweightlossaftercombustionat375°Cfor16h(Ball1964).

Statistical Analyses

RegressionequationsweredevelopedusingPROCMIXEDinSAS(Littellandothers1996),atthe0.05significancelevel,andLSMEANSwasusedtocomparevegetationtypeswithinsoildepths.WhenanalyzingresultsforCa,weexcluded



treatmentstoraisesoilpHbecausetheCa(OH)2wouldhaveartificiallyelevatedCalevels.Transformationsofvariableswereexploredtoachievehomogeneityoferrorvariance,normalityandindependenceoferrorandblockeffects,andtoobtainadditivityofeffects(Littellandothers1996).

Results and Discussion ___________________________________________

Soil pH Changes

FieldstudiesintheGFMindicatethatsubstantialpHfluxesoccurthroughouttheyear(figs.1and2)(Fergusonandothers,thisproceedings).ResultsofourcontrolledstudyconfirmourinitialobservationthatchangesinvegetationtypeinfluenceforestsoilpH(table2).BeforetreatmentwithSorCa(OH)2,the0-5cmsoilpHwaslowestinthenaturalbrackenfernglade(5.0)andfern-invadedclearcut(4.7)ontheClearwaterNationalForest,intermediateontheNezPerceNationalForestundisturbedarea(5.4)andconeflower-invadedclearcut(5.4),andhighestontheClearwaterNationalForestundisturbedforest(6.3)andpartialcut(6.4)(table2).SoilpHatthe10-15cmdepthfollowedthesametrends.AftertreatmentwithSorCa(OH)2and90daysofincubation,finalpHvaluesrangedfrom3.6to6.1(table2).MostpHchangesoccurredwithin45daysofstartingtheincubationperiod,butthelowestpHvalueswereachievedafter85days.

Interestingly,untreatedsoilsfromtheClearwaterNationalForestundisturbedandpartialcuttreatmentsexhibitedadeclineinsoilpHduringincubationinthegreenhouse.Forexample, theinitialaveragepHintheundisturbedforestwas6.3,butattheendoftheincubationperiod,thehighestpHvaluewas5.4.This“natural”decreaseintheabsenceofvegetationandbioticprocessesissimilartothepHdecreasesshowninfigures1and2.Inthesetwofigures,winterpHvaluesaveragearound6,butdropbelow4duringthegrowingseason.TheseseasonalpHfluxesmaybedrivenbyinputsofacidlitterfrombrackenfernandwesternconeflower.Inaddition,thesetwospecieslikelytakeuphighratesofnutrientsfrom

Table 2—Initial and final soil pH ranges after treatment with S or Ca(OH)2.

National Forest Vegetation type Initial pH Final pH range - - - - - -0-5 cm depth- - - - - - - -Clearwater Undisturbed forest �.� �.7 - �.4Nez Perce Undisturbed forest �.4 �.� - �.�Clearwater Partial cut �.4 �.� - �.0Clearwater Natural bracken fern glade �.0 �.7 - �.0Clearwater �0-year-old bracken fern-invaded clearcut 4.7 �.7 - �.�Nez Perce 21-year-old coneflower-invaded clearcut �.4 �.� - �.� - - - - - - 10-15 cm depth - - - - - -Clearwater Undisturbed forest �.� �.� - �.�Nez Perce Undisturbed forest �.� �.� - �.�Clearwater Partial cut �.2 �.� - �.2Clearwater Natural bracken fern glade 4.9 �.9 - �.1Clearwater �0-year-old bracken fern-invaded clearcut 4.� �.7 - �.1Nez Perce 21-year-old coneflower-invaded clearcut �.� �.� - �.1



thesoil,whichmayalsocontributetoacidconditions(Gilliam1991).AlthoughforestharvestingcanlowerpH,subsequentinvasionbybrackenfernorwesternconeflowerappearstocontributetoandmaintainlowpHrelativetoundisturbedforestsoils.However,thelaboratorydataindicatesthatsomepHchangeswithinthesesoiltypesarepossibleevenwithoutvegetationfacilitatingthechange.

Carbon and Nitrogen

ThereweresignificantdifferencesintotalCconcentrationamongthevegetationtypes(table3).SoilCconcentrationwashighestunderthefern-invadedclearcutatbothdepths (11.27percent0-5cmdepth;10.00percent10-15cmdepth).TotalCwas lowestat the10-15cmdepthwhereconiferswerepresent (bothundisturbedforestsandpartialcut).Thesoilsthatsupportthehighestvegetationturnoverrates(brackenfernandwesternconeflower)hadsimilarCconcentrationsatbothdepths,whilevegetationtypeswithconiferspresenthadabouttwiceasmuchCinthesurfacesoilcomparedtothe10-15cmdepth.

Thefern-invadedclearcuthasapproximately390g/m2ofbrackenfrondbiomassaddedtothesoilannually(Znerold1979).OntheClearwaterNationalForest,rhizome and fine root biomass in the fern-invaded communities averaged4000g/m2(Jimenez2005);inthenaturalglade,rhizomeandfinerootbiomassaveraged3200g/m2.ItisnotsurprisingthatthisvegetationtypehashigherCcon-centrations.WeexpectedthatthenaturalbrackenferngladewouldhaveasmuchCasthefern-invadedclearcut,butthiswasnotthecase.Thenaturalbrackenferngladesoilappearstobeatanintermediatepointbetweentheundisturbedforestandthefern-invadedclearcut.TheseresultsaresimilartoCandNdatacollectedfromnearbysiteswithintheGFM(Johnson-Maynardandothers1997).Oneex-planationmaybethatthenaturalbrackenferngladehasreachedasteadystate.

Table 3—Mean C, N, Ca, Mg, and K in the control treatment, by vegetation type and depth. Each mean is an average of three replications.

National Vegetation Forest type Carbon Nitrogen Calcium Magnesium Potassium

- - - - - - percent - - - - - - - - - mg/kg - - - 0-5 cm depthClearwater Undisturbed forest �.�0 a‡ 0.40 a 12.21 d 1.12 b 1.�4 bNez Perce Undisturbed forest 7.�7 b 0.74 c 14.1� e 1.14 b 0.99 aClearwater Partial cut �.2� a 0.�� a 7.�� b 0.74 a 0.99 aClearwater Natural bracken fern glade 7.9� b 0.�1 b �.�� a �.29 d 2.77 cClearwater Bracken fern-invaded clearcut 11.27 c 0.�9 bc �.70 a 2.�4 c 2.�9 cNez Perce Coneflower-invaded clearcut �.17 a 0.�� a 9.1� c 0.92 a 1.02 a 10-15 cm depthClearwater Undisturbed forest �.17 a 0.24 a �.41 c 0.74 d 1.22 cNez Perce Undisturbed forest �.90 b 0.22 a �.�� c 0.41 a 0.71 bClearwater Partial cut �.�� ab 0.2� a �.79 b 0.49 c 0.71 bClearwater Natural bracken fern glade �.90 c 0.4� c 4.2� b 1.�� e 2.20 eClearwater Bracken fern-invaded clearcut 10.00 d 0.�7 d 2.72 a 0.77 d 1.�0 dNez Perce Coneflower-invaded clearcut �.27 c 0.�4 b �.�� c 0.4� b 0.4� a‡ Within soil depth, means followed by different letters are significantly different (p = 0.05) using LSMEANS.



Becausebrackenfernproduceshighlevelsofallelopathicchemicals(FergusonandBoyd1988),itisperhapsbecomingautotoxic(GliessmanandMuller1978),whichresultsinlessfrondbiomass(naturalglade678g/m2;fern-invadedclearcut916g/m2(Jimenez2005))andlessorganicCincorporatedintothesoil.Thesetwotypesofbrackenfernstands(naturalgladeandinvadedclearcut)mayalsobeatdifferentlifecyclestages(Atkinson1986).

HighersoilCconcentrationsinthefern-invadedclearcutareconsistentwiththedevelopmentofnonallophanicsoilcharacteristicsfollowinginvasion(Nanzyoandothers1993;Johnson-Maynardandothers1997;Dahlgrenandothers2004).IncreasedlevelsofCinthebrackenfernsites,ascomparedtoundisturbedsoils,may increase the potential for preferential formation of Al-humus complexes(Dahlgrenandothers1993).

ForestsitesinvadedbywesternconeflowermaintainedmoderatelevelsofCthroughoutthesamplingdepths.Atthe10-15cmdepththeconeflower-invadedclearcuthadnearlytwiceasmuchCastheundisturbedforestsoil(table3).Car-bonwasdistributeddeeperinthesoilprofileintheconeflower-invadedclearcutthanonthebrackenfernsites.Thismaybebecausetheconeflower-invadedsitehadgreatersurfaceandsubsoilmixingcausedbypocketgophers(FergusonandAdams1994)orbecauseofslightlylesssurfacevolcanicashdeposition(Sommer1991).

Foreachvegetationtype,therewasgenerallymoreNinthe0-5cmdepththaninthe10-15cmdepth,withtwonotableexceptions.Boththefern-invadedclearcutandtheconeflower-invadedclearcutsoilshadasmuchNinthe10-15cmdepthasthesurfacesoil.Thisislikelycausedbythelargeannualinputsofforbbiomassthatusuallyoccurinnewlyinvadedclearcuts(Attiwillandothers1985).

RegressionanalysesshowedthattotalCandNwereunchangedafteralteringpH.Thisresultwasnotunexpectedsincewedidnotaddorganicmatter.

Base Cation Concentrations

Basedonthecontrolsamples,vegetationtypedoesinfluencesoilCa,Mg,andKconcentrationsinthesevolcanicashsoils(table3).Forbothsoildepths,theferngladeandthefern-invadedclearcuthadsignificantlymoreKandMgthansoilsfromundertheothervegetationtypes.Incontrast,Cacontentwasgreatestinsoilsunderbothundisturbedforests.

Regressionanalysisshowedthatbasecationconcentrations(Ca,Mg,andK)didnotchangeasaresultofpHchanges(datanotshown).OurresultsdifferfromthoseofMohebbiandMahler(1988)whofoundastrongcorrelationbetweenpHandcationconcentrationafterartificiallychangingpHinaloessalsoil.Intheirstudy,aspHincreased,bothKandMgdecreased;however,CasharplyincreasedfrompH5to7.ItalsoincreasedafterpHdroppedbelow3.5.Itisunusualthatsoilconsistingofvolcanic-ashinfluencedmaterials,whichhaveavariablecharge,didnotshowamarkedreductionintheretentionofexchangeablebaseswithdecreasingpH.Thisindicatestheremaybeenoughpermanentchargemineralstomaintainbaseconcentrations.Intheferngladeandthefern-invadedclearcut,soilsmaybedevelopingpropertiestypicalofnonallophanicAndisols(Johnson-Maynardandothers1997).

LackofpH-drivenchangesincationconcentrationinourstudymayberelatedto high organic C content of the ash-influenced soil (Shoji and others 1993).Theoretically,oncethesesitesareharvested,substantiallossesofbasiccationsare



possible.Bothlossofnutrientsfromabovegroundpools(Boyleandothers1973;Federerandothers1989)andincreasedleachinglosseshavebeenreportedafterharvesting(Hendricksonandothers1989).However,cationsmayberedistrib-utedintonew,immediateregrowthofbrackenfernorwesternconeflowerafterharvestingandnotlostfromthesite(Johnsonandothers1997).

Available Phosphorus

Phosphorus(P)amountsvariedsignificantlyamongvegetationtypesandsoildepths.ThemeanvaluesforPinthecontroltreatmentareshownintable4.ThelargestPmeansareinthe0-5cmdepthundertheundisturbedforests(NezPerceNationalForest3.17μg/gandClearwaterNationalForest3.03μg/g).Thefernglade(2.73μg/g)andfern-invadedclearcut(2.20μg/g)wereintermediateinP,andthelowestmeanswereintheconeflower-invadedclearcut(1.87μg/g)andpartialcut(1.70μg/g).

RegressionanalysesshowedthatPincreasedwithdecreasingpH.ResponseofsoilPwassimilaratbothsoildepths;therefore,regressionequationsareshownonlyforthe0-5cmdepth(table5).Thevegetationtypeshadsimilarresponse

Table 4—Mean P, potentially mineralizable N (PMN), nitrate (NO�-N), aluminum (Al), and total acidity in the control treat-ment, by vegetation type and soil depth. Each mean is the average of three replications.

National Vegetation Forest type P PMN NO3-N Al Total acidity

µg/g - - - - - - mg/kg - - - - - - - - - - - -cmol/kg - - - - - 0-5 cm depthClearwater Undisturbed forest �.0� c‡ 100.41 b �7.7� a 0.17 a 0.2� aNez Perce Undisturbed forest �.17 c �0.1� ab 172.01 b 0.22 a 0.41 abClearwater Partial cut 1.70 a 14.9� a 10�.1� a 0.�4 ab 0.�� bcClearwater Natural bracken fern glade 2.7� c 7.�� a 2�0.07 bc 0.�4 b 0.7� cClearwater Bracken fern-invaded clearcut 2.20 b ��.�2 ab 24�.99 c 1.14 c 1.77 dNez Perce Coneflower-invaded clearcut 1.�7 ab 2.14 a 97.�1 a 0.2� a 0.�4 ab 10-15 cm depthClearwater Undisturbed forest 1.�0 c �.�� a 24.0� a 0.1� a 0.�1 aNez Perce Undisturbed forest 2.10 d ��.�� a ��.�1 a 0.�1 ab 0.9� abClearwater Partial cut 1.40 b 2�.04 a �1.�� ab 0.�0 a 0.�1 aClearwater Natural bracken fern glade 1.�0 b �.97 a 1��.94 c 1.�� b 1.70 bClearwater Bracken fern-invaded clearcut 2.�� e 192.�0 b 127.4� bc �.�� c 4.22 cNez Perce Coneflower-invaded clearcut 0.9� a 29.�1 a 47.�1 ab 0.21 a 0.�1 a‡ Within each soil depth, means followed by different letters are significantly different (p = 0.05) using LSMEANS.

Table 5—Regression equations for 0-� cm depth (bold lines on figs. �, �, and �).

Y= exp (βo +β1*pH) and Y, βo, and β1 take on the following values:

Definition Dependent(Y) βo β1

P concentration PHOS 2.�7�9 –0.��12Potentially mineralizable N PMN 10.449� –1.44�7NO�-N concentration NO�-N –7.14�2 2.2212KCl-extractable Al ALUM 10.�40� –2.2�14Total acidity ACID 9.9�7� –2.0�2�



surfaces(fig.3).SoilfromtheClearwaterNationalForestundisturbedforesthadthehighestavailablePwhenpHdroppedbelow4.0.Bothhumusandallophanecontentinvolcanicash-influencedsoilsaffectPavailabilityandthehighlevelofCinthefern-invadedclearcutsoilmaybesorbingP(Wada1985).Theseresultsarequitedifferentfromtheloessalsoilsthathaveastronglinearincreaseinavail-ablePaspHincreases(MohebbiandMahler1988).Forvolcanicash-influencedsoils,thepHdependencyofphosphatesorptionishighestbetweenpH3and4,andgenerallydecreaseswithincreasingpH(Nanzyo1987).Thisisespeciallytrueforallophanicash-influencedsoilsascomparedtononallophanicash-influencedsoils(Nanzyoandothers1993).

Insoilsconsistingofweatheredvolcanicash,Psorptionisamajorsoilfertilityproblem(AndreggandNaylor1988).Inmostmineralsoils,organicmatterisanimportantreservoirforP.However,inmanyvolcanicash-influencedsoils,organicmatterprotectsPfromsorption(Moshiandothers1974).Thisappearstobethecaseforthesesoilsaswell.

Figure 3—Regression equations for available P concentration (µg/g) of the 0-� cm depth as affected by pH manipulation by vegetation type. The bold line is the regression for all vegetation types.



Potentially Mineralizable N and Nitrate-N

PotentiallymineralizableN(PMN)concentrationsvariedwidelyamongveg-etationtypesandsoildepths(table4).Forexample,inthecontrolsoilforthe0-5cmdepth,PMNrangedfromalowof2.14mg/kgintheconeflower-invadedclearcutto100.41mg/kgintheundisturbedforestontheClearwaterNationalForest.AmountsofPMNatthe0-5cmsoildepthwaslowinthefernglade,butintermediateinthefern-invadedclearcut.

Nitrate-N(NO3-N)alsovariedamongvegetationandsoildepths.Thelargestmeansatthe0-5cmdepthforthecontrolsoil(table4)wereinthefern-invadedclearcut(246.99mg/kg)andfernglade(230.07mg/kg),andthelowestmeanwas87.73mg/kgintheundisturbedforestsoilfromtheClearwaterNationalForest.MeansforNO3-Natthe10-15cmdepthwerelowerthanthe0-5cmdepth,butthetrendsweresimilar.

AnalysesshowedthatPMNconcentrationsdeclinedrapidlyassoilpHincreasedabove5.0and,incontrast,soilNO3-NconcentrationincreasedrapidlyabovepH5.0,exceptintheferngladeandfern-invadedclearcutwherethischangeinNformoccurredbelowpH4.5(fig.4a-f).WhilethesoilsinbothundisturbedforestsandthepartialcutforestsexhibitedathresholdlevelofpH5.0forsub-stantialchangesinthequantityofavailableN,thetwositeswithbrackenfernvegetationtypesandtheconeflower-invadedclearcuthadsteadychangesinNaspHincreased.Bothsoildepthshavesimilarregressioncurvesforeachvegetationtype;therefore,onlythe0-5cmsoildepthisshown(table5).

The sharpdecline inPMN from theseash-influenced sites isdifferent fromthenorthernIdaholoessalsoils,whichhadasignificantincreaseinPMNaspHincreasedfrom3.0to7.0(MohebbiandMahler1988).Thismayindicateadiffer-enceinorganicmatterconcentrationfromloess-grasslandareastoash-forestedareas,andsuggeststhatorganicNinvolcanicash-influencedsoilsmaybefairlyresistanttomicrobialdecompositionbecauseoftheAl-organiccomplexesthatareformed(Shojiandothers1993).

Whilesoilfrommostofthevegetationtypesshowacrossoverinrelativeabun-danceofPMNandNO3-NaroundpH5.0,thebracken-ferndominatedvegetationtypeschangebelowpH4.5.IncreasedNO3

-NanddecreasedPMNathigherpHvaluesisconsistentwithresultsofacidrainandsoilnutritionstudies(Schier1986;Marx1990).NitrogenmineralizationoftenincreaseswhensoilpHisraised(MontesandChristensen1979),butoccasionallyhasbeenshowntodecrease(AdamsandCornforth1973).NitrificationisalsopHsensitiveandgenerallyincreasesaspHisraisedfromveryacidtomoderatelyacid(Robertson1982).Inthisstudy,theclearcutsinvadedwitheitherbrackenfernorwesternconeflowerlikelyexhibitthisNchangeeachyearaspHchanges(BinkleyandRichter1987).

Aluminum and Total Acidity

KCl-extractableAl (whichreflectsexchangeableAl)and totalacidityvariedsignificantlyamongvegetationtypesandsoildepths.Meanvaluesinthecontroltreatments are shown in table4.Aluminumand total acidity are significantlyhigherintheferngladeandfern-invadedclearcut,forbothdepths.MeanAlandacidvaluesaregenerallyhigherinthe10-15cmdepthsoilascomparedtothe0-5cmdepth.



Figure 4—Soil NO�-N and PMN concentration (mg/kg) in the 0-� cm depth as affected by pH manipulation, by vegetation type (a) Clearwater National Forest, undisturbed, (b) Nez Perce National Forest, undisturbed, (c) Clearwater National Forest, partial cut, (d) Clearwater National Forest, bracken fern glade, (e) Clearwater National Forest, bracken fern-invaded clearcut, (f) Nez Perce National Forest, coneflower-invaded clearcut.

(a) (b)

(c) (d)

(e) (f)



RegressionanalysesshowedthatAlwashighlycorrelatedwithchangesinpH(table5)inallvegetationtypes.AluminumincreasedexponentiallywhenthepHdecreasedbelow4.5(fig.5).Both0-5cmand10-15cmdepthshadsimilarcurves;therefore,onlythe0-5cmsoildepthregressionlinesareshown.Volcanicash-influencedsoilscontainhighlevelsofAl-containingmaterialsthatcanundergodissolutionunderacidic(lessthatpH5.0)conditions(Tisdaleandothers1993).Inthesesoils,verylittleexchangeableAlwasdetectedabovepH5.0.BasedoncontinuoussoilmeasurementsofpH(figs.1and2),soilsunderbrackenfernandconeflowervegetationhaveapHbelow5.0eachgrowingseason.SoilpH5.0isgenerallyconsideredtobethecriticalpointforAltoxicitytowoodyvegetation(Wolt1994).

Ingeneral,woodyplantspeciesappeartobemoretolerantofAlthanagricul-turecrops(McCormickandSteiner1978;Ryanandothers1986),andthereisconsiderablevariationinAltoleranceamongtreespecies(McCormickandSteiner1978;Steinerandothers1984;ArpandOuimet1986;Hutchinsonandothers1986;Schaedleandothers1989;Raynalandothers1990).Aluminumtoxicityalterstreerootanatomy,whichfirstoccursintheroots(Hutchinsonandothers1986;Schaedleandothers1989;McQuattieandSchier1990;NoskoandKer-shaw1992;Schier1996).TheresultofAltoxicityisimpairedrootdevelopment,resultinginreducedrootlengthandformationofashallowrootsystem.Athigh

Figure 5—Exchangeable Al concentration (cmol/ kg) in the 0-� cm depth as affected by pH, by vegetation type. The bold line is the regression for all vegetation types.



Allevels,mitosisisalmostcompletelyinhibited.Leamy(1988)notedthatinvol-canicash-influencedsoils,Altoxicitymayoccuratconcentrationsof2cmol/kgsoil,andthisvalueisusedasathresholdinSoilTaxonomyforidentifyingthoseAndisolsinwhichAlphytotoxicitymayoccur(SoilSurveyStaff2003).Aluminumlevelsfoundinthislaboratorystudyaremuchhigherthan2cmol/kgwhenpHdecreasedbelow5.0andindicatesastrongpotentialforAltoxicityintheseash-influencedsoilsaspHvaluesdecline.

ThevariousstudiesonAltoxicityintreespeciesaredifficulttocomparebecauseofdifferent studymethods,unitsofmeasure,growthmedia, lengthofexperi-ments,andageoftrees(Schaedleandothers1989;NoskoandKershaw1992).However,oneimportantfindingisthatyoungseedlingsaremoresensitivetoAltoxicitythanolderseedlings.Forexample,Schier(1996)foundthatAlconcentra-tionsof0.32mM/linhibitedrootbiomassinnewlygerminatedredspruce(Picea rubens)seedlings,whilethethresholdwas2.1mM/lin1-year-oldseedlings.ItseemsreasonabletoassumethatconiferseedgerminatingonGFMsitescouldbeimpactedbylowconcentrationsofAl.Aluminumtoxicity,allelopathiccom-pounds,andcompetitioncouldcombinetoeliminatethenaturalestablishmentoftreesandotherwoodyplantspeciesonthesesites.

Regressionanalyses for totalacidity followed thesame trendasextractableAl(fig.6),andonlythe0-5cmsoilregressionlinesareshown.Theregressionequationfortotalacidityisshownintable5.Mostoftheacidityinthesesoils

Figure 6—Total acidity (cmol/kg) in the 0-� cm depth as affected by pH manipulation by, vegetation type. The bold line is the regression for all vegetation types.



occursasAl.TherelationshipbetweenexchangeableAlandtotalacidityisnotunusual sincemost of the exchangeable acidity is derived fromAl andHontheexchangesites(BinkleyandRichter1987).Changesinexchangeableaciditygenerallyoccuroveralongperiodoftimeandareduetoacidificationthroughweathering,leaching,cationuptake,oratmosphericdeposition(Richter1986).RapidchangesinacidityoccuroccasionallybyotherH-ioninputs.IntheGFM,bothbrackenfernandwesternconeflowervegetationhavethepotentialtoinputH-ionsviaorganicacidproductionoradditionsofhighamountsoforganicCthroughyearlyvegetationcycles.

Summary ______________________________________________________Analysis of unaltered soil samples supporting undisturbed grand fir forest

andbrackenfern/westernconeflowerplantcommunitiessuggeststhatchemicalpropertiesofGFMforestsoilarealteredthroughinvasionofsuccessionalplantspeciesaftertimberharvestorotherdisturbance.Changesinsoilconditionsaresimilartoadepthof15cm.SeasonaldecreasesinsoilpHunderbrackenfernandwesternconeflowervegetationtypesmostlikelycauseareleaseofexchangeableAlatlevelstoxictowoodyvegetation.HighlevelsofC,exchangeableAl,andtotalacidityunderthesetwovegetationtypesmayalsobefacilitatingalocalizedconversionoftheseash-influencedsoilsfromallophanictononallophanicAndis-ols.ForestedsoilsintheGFMarecapableofexhibitingthesesamecharacteristicsoncedisturbed.

Resultsofthisstudyalsoprovideinsightsintothechemicalchangesthatmayoccurinvolcanicash-influencedsoilsaspHfluctuates.Mechanismsthatcon-tributetoforb-dominatedsecondarysuccessionalplantcommunitieshavebeenidentified.Forexample, theapparentchangeinNbetweenPMNandNO3-Nhasimplicationsindeterminingwhichspeciescangrowonthesesites,asdoestheexponentialincreaseofAlbelowpH5.0.Clearly,thislaboratorystudypointsoutthepotentialforAltoxicitythatmayaccompanyseasonalpHfluctuations.Theselaboratorystudyfindingsareconsistentwithin situsoilsolutiondata,whichindicate that soils invaded by bracken fern and western coneflower undergoconversionfromallophonictononallophanicproperties(Johnson-Maynardandothers1997).However,alteringthepHofash-influencedsoilsdifferedfromal-teringloessalsoils(MohebbiandMahler1988).Thesesoil-typedifferencesarelikelyattributabletotheuniquephysical,chemical,andbiologicalpropertiesofash-influencedsoilsascomparedtothosederivedfromotherparentmaterials(Dahlgrenandothers2004).

This laboratory study highlights important characteristics of ash-influencedsoilsthatmaycontributetochangesinvegetation.Thistypeofstudy,combinedwithfieldwork,willhelpinthedevelopmentofpracticalmanagementrecom-mendations.

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Summaries of Poster Papers



William Elliot is Project Leader, Ina Sue Miller is Hydrologist, and David Hall is IT Specialist, Soil and Water Engineering Research Work Unit, Rocky Mountain Research Station, Moscow, ID.

WEPP FuME Analysis for a North Idaho Site

William Elliot, Ina Sue Miller, and David Hall

Introduction

Acomputerinterfacehasbeendevelopedtoassistwithanalyzingsoilerosionratesassoci-atedwithfuelmanagementactivities.ThisinterfaceusestheWaterErosionPredictionProject(WEPP)modeltopredictsedimentyieldsfromhillslopesandroadsegmentstothestreamnetwork.Thesimple interfacehasa largedatabaseofclimates,vegetationfilesandforestsoilpropertiestosupportthisandotherinterfaces,includingDisturbedWEPPforforestsandWEPP:Roadforroadsegmentanalyses.Thesoildatabasesforroadsanddisturbedforestedhillslopesarebasedonrainfallsimulationandnaturalrainfallstudies. TheWEPPFuMEinterfacecarriesouterosionpredictionrunsforsixforestconditions:

1.Undisturbedmatureforest 2.Wildfire 3.Prescribedfire 4.Thinning 5.Lowtrafficroads 6.Hightrafficroads

Theclimate,soiltexture,topography,roaddensity,wildfirereturninterval,prescribedfirecycleandthinningcyclearespecifiedbytheuser. TheWEPPFuMEinterfacecanbeusedanywherewithintheUnitedStatesusingtheexistingclimatedatabase.Theinterfaceisintendedtoprovideanoverviewofthesourcesofsedimentonagiven fuelmanagement site. Sedimentpredictions fromWEPPFuMEare for surfaceerosiononly.


Elliot, Miller, and Hall WEPP FuME Analysis for a North Idaho Site

Hillslope Method and Parameters _________________________________The example in this paper is an area within the Yellowpine timber sale in

northernIdaho(fig.1).ThewatershedhillslopeboundariesweredelineatedusingGeoWEPP(ageo-spatialinterfacetoolforWEPP)(fig.2).EachhillslopefromtheexamplewatershedwasexaminedusingtheFuMEmodel.Onlyonehillslopecanberunatatimeandinthisinstance,hillslopenumber22isdisplayed(fig.2).

FuMEwasrunforanindividualhillslope(number22,fig.2).Theconditionsofthemodelweresandyloamsoiltexture,hillslopelengthof708feet,hillslopegradientstartingwiththetopofthehill25,36,and20percent,a40ftbufferlengthandthedefaultroaddensity,fireandthinningcycles.

Figure 1—Unit 4 of the Yellowpine timber sale in northern Idaho.


WEPP FuME Analysis for a North Idaho Site Elliot, Miller, and Hall

Figure 2—The WEPP-FuME model windows for hillslope 22.


Elliot, Miller, and Hall WEPP FuME Analysis for a North Idaho Site

Table 1—WEPP FuME summarized results and weighted averages.

Thinning + Rx Background Thinning Rx Fire Thinning + Rx fire fire w/moderate Hill slope sedimentation effects effects w/high severity fire severity fire

- - - - - - - - - - - - - (ton/mi2)- - - - - - - - - - - (ton/mi2)* (ton/mi2)** 22 1�9 141.� 1�2.1 1��.� �2.92 2� 97.2 9�.2 99.1 100.2 �0.�2 �1 92.2 92.� 9�.2 9�.� 2�.4� �2 120.� 122.� 12�.� 129.7 ��.94 �� 11�.� 119.� 120.2 121.� �9.4� 41 104.1 10�.1 10�.1 10�.2 �1.�� 42 144.� 14�.� 144.� 14�.9 4�.�2 4� 9�.� 94.� 94.� 10�.1 29.02

Weighted averagesfor the examplewatershed 11�.7 11�.2 117.9 120.� �9.9* The projected background rate in this column assumes fuel management activities did not reduce the fire hazard by remov-ing excess fuel. The estimated background rate for this column was calculated with a high severity fire value.** The projected background rate in this column assumes fuel management activities reduce the fire hazard by removing excess fuel. Therefore, the estimated background rate for this column was calculated with a moderate severity fire value.

Note: All sedimentation estimates displayed above are calculated from the low end erosion rates of the road network.The high severity fire value was used in the background sedimentation rate calculation unless stated otherwise.

Cumulative Watershed Results ____________________________________AllhillslopesfromtheexamplewatershedwereanalyzedwithWEPPFuME.

Thesummarizedresultsandweightedaveragesfortheexamplewatershedaredisplayedintable1below.

Fromthetablewecanobservethatifamoderatefirescenariooccursevery40yearsforthewatershed,incombinationwiththeprescribedfireandthinningmanagementactivities,includingerosionfromroads,thereisa65percentdecreaseoferosionoccurringwhencomparedtothebackgroundrate.Intheeventofahighseverityfire,incombinationwiththeprescribedfireandthinningmanage-mentactivitiesincludingtheerosionfromroads,thetotalwatershedresultsina6percentincreaseofpredictederosion.Forbothexamples,thebackgroundrateincludeslowimpactroadsandthehighseverityfirescenario.


WEPP FuME Analysis for a North Idaho Site Elliot, Miller, and Hall

References ______________________________________________________Covert,S.A.;Robichaud,P.R.;Elliot,W.J.;Link,T.E.2005.Evaluationofrunoffpredictionfrom

WEPP-basederosionmodelsforharvestedandburnedforestwatersheds.TransactionsoftheASAE.48(3):1091-1100.

Elliot,W.J.2004.WEPPinternetinterfacesforforesterosionprediction.Jour.oftheAmer.WaterRes.Assoc.40(2):299-309.

Elliot,W.J.;Hall,D.E.1997.WaterErosionPredictionProject(WEPP)forestapplications.GeneralTechnicalReport INT-GTR-365.Ogden,UT:U.S.DepartmentofAgriculture,ForestService,IntermountainResearchStation.11p.

Elliot,W.J.;Hall,D.E.2005.WaterErosionPredictionProject(WEPP)FuelManagement(FuME)tool.Fuelsplanning:sciencesynthesisandintegration;environmentalconsequencesfactsheet12.Res.NoteRMRS-RN-23-12-WWW.FortCollins,CO:U.S.DepartmentofAgriculture,ForestService,RockyMountainResearchStation.2p.

Elliot,W.J.;Robichaud,P.R.2004.Theeffectivenessofpostfiremitigationtreatments.Presentedatthe2004BAERTrainingWorkshop;2004April30;Denver,CO.

Elliot,W.J.;Robichaud,P.R.2004.Evaluatingsedimentrisksassociatedwithfuelmanagement.Fuelsplanning:sciencesynthesisandintegration;environmentalconsequencesfactsheet8.Res.NoteRMRS-RN-23-8-WWW.FortCollins,CO:U.S.DepartmentofAgriculture,ForestService,RockyMountainResearchStation.2p.

Elliot,W.J.;Miller,I.S.2002.EstimatingErosionImpactsfromImplementingtheNationalFirePlan.2002ASAEannualinternationalmeeting/CIGRXVthworldcongress;2002July28-31;Chicago,IL.St.Joseph,MI:ASAE:ASAEmeetingpaperno.02-5011.

Elliot, W. J.; Miller, I. S. 2004. Measuring Low Rates of Erosion from Forest Fuel ReductionOperations,2004ASAE/CSAEAnnualInternationalMeeting;2004August1-4;Ottawa,Ontario,Canada:ASAEpapernumber045018.

Laflen,J.M.;Elliot,W.J.;Flanagan,D.C.;Meyer,C.R.;Nearing,M.A.1997.WEPP–Predictingwatererosionusingaprocess-basedmodel. JournalofSoil andWaterConservation.52(2):96-102.

McDonald,G.I.;Harvey,A.E.;Tonn,J.R.2000.Fire,competitionandforestpests:Landscapetreatmenttosustainecosystemfunction.In:Neuenschwander,L.F.;Ryan,K.C.,eds.Proceed-ingsfromtheJointFireScienceConferenceandWorkshop;1999June15-17;Boise,ID.Onlineat<http://jfsp.nifc.gov/conferenceproc/T-11McDonaldetal.pdf>.AccessedJune,2004:17p.

Spigel, K. M. 2002. First year postfire erosion rates in Bitterroot National Forest, Montana.Madison,WI:UniversityofWisconsin.147p.MSThesis.



William Elliot is Project Leader, Ina Sue Miller is Hydrologist, and Brandon Glaza is Civil Engineer, Soil and Water Engineering Research Work Unit, Rocky Mountain Research Station, Moscow, ID.

Erosion Risks in Selected Watersheds for the 2005 School Fire Located Near Pomeroy,

Washington on Predominately Ash-Cap Soils

William Elliot, Ina Sue Miller, and Brandon Glaza

Geo-WEPP Spatial Analysis

Alimitederosionpotentialanalysiswascarriedoutonthe50,000acreSchoolFire.ThreeWEPPinterfaceswereusedfor theanalysis,aGISwizard,anonline interfaceandawin-dowsinterface.TenwatershedswithinthefireareaweremodeledwiththeGeoWEPPtool(ageo-spatialinterfaceforWEPP,WaterErosionPredicationProject).Thewatershedscovered18,823acres,orabout38percentofthetotalburnedarea.Hillslopeswerespecifiedhigh,moderateorlowburnseveritybyexaminingtheBAER(BurnedAreaEmergencyResponse)severitymap. ByconsultingwiththeBAERspecialists,watershedsofgreatestinterestwereidentified.OnesetincludedfourwatershedsdischargingintotheTucannonRiverfromthewesternside,in-cludingSchoolCreek,whichflowedintotheTucannonRiverattheTucannonGuardStation.AsecondsetincludedthreewatershedsflowingintotheTucannonRiverfromtheeastside,southoftheTucannonGuardStation.ThethirdsetofwatershedswerelargerandincorporatedDryCreek(atributarytoCummingsCreek),CummingsCreekandPatahaCreek.


Elliot, Miller, and Glaza Erosion Risks in Selected Watersheds for the 200� School Fire Located Near Pomeroy, Washington…

ERMiT Hillslope Analysis – Online Interface ________________________TheERMiT(ErosionRehabilitationManagementTool;August,2005version)

resultsforasinglestormerosionpredictionaregivenintable1below.Table2providesanoverallaverageofallERMiT runs.Hillslopeswerespecifiedhigh,moderateorlowseverityfromtheBAERseveritymap.Anaverageofabout12randomlyselectedhillslopesor5percentofthehillslopesonlargerwatersheds,wererunwithERMiTforeachwatershed,withtheexceptionofupperPataha.IntheupperPatahawatershed,only10hillslopeswereidentifiedasmoderateorseverelyburned.Themulchingtreatmentassumedanapplicationroleof0.9tons/acrefollowingthefire.Onaverage,thereisa20percentchancethattheerosionrateinthewatershedwillbegreaterthan7tonsperacreifleftuntreated,andonlya10percentprobabilitythaterosionwillexceed10tons/acifleftuntreated.

Table 1—ERMiT single storm erosion predictions – August-200� version.

Untreated Seeded Mulched Year Year Year Drainage Exceedance 1 2 1 2 1 2

- - - - - - - - - - - - - - - - - (tons/ac) - - - - - - - - - - - - - - - - - -

Tucannon West � 10% Mean 12.9� 9.00 12.9� 4.9� 1.�4 �.11 Std Dev �.00 �.97 �.00 �.�2 0.�� 2.1�

20% Mean �.�7 �.7� �.�7 2.27 0.00 0.92 Std Dev �.�� .9� �.�� 1.7� 0.00 0.79

Tucannon West 2 10% Mean 10.0� 7.24 10.0� �.9� 0.99 2.4� Std Dev �.40 �.�0 �.4 4.0� 1.02 2.�0

20% Mean �.�� 4.�7 �.�� 1.7� 0.00 0.70 Std Dev �.22 4.71 �.22 2.09 0.00 0.��

Tucannon West 1 10% Mean 14.14 9.�1 14.14 �.27 1.�� .1� Std Dev �.11 �.9� �.11 �.79 1.�� 2.�1

20% Mean 9.2� �.2� 9.2� 2.21 0.00 0.90 Std Dev �.79 4.44 �.79 1.99 0.00 0.�7

School Canyon 10% Mean �.00 4.1� �.00 2.21 0.�� 1.�4 Std Dev 7.00 �.24 7.00 �.�� 0.74 2.04

20% Mean �.77 2.�1 �.77 0.92 0.00 0.�7 Std Dev �.1� �.�4 �.1� 1.�4 0.00 0.�7

Grub Creek 10% Mean 10.71 7.70 10.71 4.�� 1.10 2.�7 Std Dev �.�1 �.2� �.�1 �.�7 0.9� 2.�7

20% Mean 7.�1 �.1� 7.�1 1.9� 0.00 0.7� Std Dev �.02 4.�� .02 1.9� 0.00 0.�4

Hixon Creek 10% Mean �.71 4.49 �.71 2.0� 0.�� 1.�9 Std Dev �.�1 �.7� �.�1 �.41 1.�4 2.41

20% Mean 4.10 2.4� 4.10 0.9� 0.00 0.�7 Std Dev �.7� 4.0� �.7� 2.00 0.00 0.7�

(continued)


Erosion Risks in Selected Watersheds for the 200� School Fire Located Near Pomeroy, Washington… Elliot, Miller, and Glaza

Table 2—Average of ERMiT runs.


- - - - - - - - - - - - - - - - - (tons/ac) - - - - - - - - - - - - - - - - - -

Means of ten sets of 10% Mean 10.�2 7.�� 10.�2 4.�� 1.�1 2.9�ERMiT runs Std Dev 2.�0 1.�� 2.�0 1.24 1.0� 1.24

20% Mean 7.0� 4.�0 7.10 1.99 0.1� 0.�� Std Dev 1.�� 1.11 1.�� 0.72 0.�1 0.40

Tucannon East 10% Mean �.22 �.72 �.22 2.90 0.72 1.�2unnamed Std Dev �.44 �.24 �.44 �.9� 0.�9 2.��

20% Mean �.2� �.44 �.2� 1.22 0.00 0.�1 Std Dev �.94 4.49 �.94 1.97 0.00 0.��

Upper Cummings 10% Mean 10.2� �.94 10.2� �.99 1.04 2.�4Creek Std Dev �.0� 4.42 �.0� 2.�2 1.0� 1.71

20% Mean �.70 4.7� �.70 1.�� 0.00 0.�1 Std Dev 4.1� �.07 4.1� 1.2� 0.00 0.��

Dry Creek 10% Mean 11.�2 7.77 11.�� .2� �.0� 4.�� Std Dev �.�9 �.0� �.�� 4.2� 2.7� �.�9

20% Mean �.�7 4.�1 7.�0 2.70 0.7� 1.�1 Std Dev �.7� 4.07 �.77 2.71 1.0� 1.�7

Upper Pataha 10% Mean 1�.�� 9.4� 1�.�� .�4 �.�9 �.�9 Std Dev �.17 4.1� �.17 �.10 1.9� 2.7�

20% Mean 9.02 �.�0 9.02 �.40 0.7� 1.�� Std Dev �.90 2.�� .90 1.70 0.�4 0.�1

Table 1 (Continued).


- - - - - - - - - - - - - - - - - (tons/ac) - - - - - - - - - - - - - - - - - -

WEPP Windows Analysis ________________________________________TheWEPPwindowsinterfacewasrunforeachwatershedtoestimatereturn

periodsforpeakrunoffrates.Theseresultswerecombinedwithothermethodstomakefinalrunoffpredictions.

Conclusions _____________________________________________________TheGeoWEPPtoolallowstheuser toquicklyestimatehillslopeparameters

foruseintheERMiTprogram.TheresultsfromtheERMiTprogramshowthatmulchingwillhavemajorbenefits in reducingerosion,especiallyon thehighseverityareas.Ontheotherhand,erosionrisksonlowseverityburnedslopeswereprojectedasbeingminimal.


Elliot, Miller, and Glaza Erosion Risks in Selected Watersheds for the 200� School Fire Located Near Pomeroy, Washington…

References ______________________________________________________Elliot,W.J.;Cuhaciyan,C.O.;Robichaud,P.R.;Pierson,F.B.;Wohlgemuth,P.M.2001.Modeling

ErosionVariabilityafterFire.Presentationatthe2001ASAEInternationalMeeting;2001July30-August1;Sacramento,CA.

Foltz,R.B.;Elliot,W.J.1999.ForesterosionprobabilityanalysiswiththeWEPPModel.Presentedatthe1999ASAE/CSAEAnnualInternationalMeeting,PaperNo.995047.St.Joseph,MI:ASAE.

Laflen,J.M.;Elliot,W.J.;Flanagan,D.C.;Meyer,C.R.;Nearing,M.A.1997.WEPP–Predictingwatererosionusingaprocess-basedmodel.JournalofSoilandWaterConservation.52(2):96-102.

Renschler,C.S.2004.TheGeo-spatialinterfacefortheWaterErosionPredictionProject(GeoWEPP).Onlineat<http://www.geog.buffalo.edu/~rensch/geowepp/>.AccessedJune,2004.

Robichaud,P.R.;Elliot,W.J.;Pierson,F.B.;Hall,D.E.;Moffet,C.A.2006.ErosionRiskManagementTool(ERMiT)Ver.2006.01.18.Onlineat<http://forest.moscowfsl.wsu.edu/fswepp/>.Moscow,ID:U.S.DepartmentofAgriculture,ForestService,RockyMountainResearchStation.

USDAARSNationalSoilErosionResearchLaboratory.2004.WEPPSoftware.Onlineat<http://topsoil.nserl.purdue.edu/nserlweb/weppmain/wepp.html>.AccessedJune,2004.



Richard E. Miller, USDA Forest Service, PNW Research Station (retired), Olympia, WA.

Conference Wrap-upRichard E. Miller

Mypurposeistwofold:toreviewkeymessagesfrompreviousspeakersandtooffersomeconceptsthatmayhelpyoulinkrecentlyacquiredinformation. WhenMt.Mazamaeruptedabout7,000yearsago,itsairborneashandpumicefellonawidevarietyofexistingsoils.ThisMazamatephrawasanewparentmaterialforsoildevelop-ment(fig.1).Atsomelocations,theoriginaldepositionwasredistributedby:gravity,wind,water,plants,oranimalactivities,includingthoseofhumans.SoilatanyspecificlocationintheInlandWestisaresultofthesesoil-formingfactorsandtheirmanypossibleinteractions.

Figure 1—Soil-forming factors (Jenny 1941).


Miller Conference Wrap-up

Major Take-Home Messages _____________________________________ 1.Ash-derivedsoilsareextensive,variable,anddifferentfromsoilsderived

fromotherparentmaterials. 2.Activities(equipment,fire)canchangesoilpropertiesandfunctions. 3.Consequences of soil changes for vegetative growth or soil erosion are

uncertain,becausetheyareseldomquantified. 4.Hence, optimum allocation of preventative or restorative efforts is

uncertain.

What is a Forester to do? ________________________________________Assumingyourintentistoprotectandmanagesoilatspecificlocations,how

willyouuseinformationgainedatthisconference?Canyoustatefactsandex-plainrelationshipsamongthesefacts?Willthisnewinformationchangeoraffectyourfuturedecisionsaboutprescribingorcontrollingactivitiesonash-derivedorash-influencedsoils?

Mostforestersandlandmanagersareconcernedaboutyield…ofwood,forageandprotectivevegetation.Mostrecognizethatyieldataspecificlocationdependsonnumerousfactorsandtheirinteractions(fig.2).Severalspeakersreviewedtheeffectsonsoilpropertiesofeitherheavyequipmentusedinharvestingorofwildandprescribedfire.Youshouldrecognizethatachangeinsoilpropertiesisachangeinoneofseveralfactorsthatcontributestoyield.Despitevisuallyapparentormeasuredchangesinsoilcharacteristics(forexample,bulkdensity,resistance,organicmatter)orfunctions,however,yieldmaynotchange.Otherfactorsthatalsoaffectyieldatagivenlocationcanbeenhancedbyorcompensateforthe

Figure 2—Factors that set productivity or yield (Jenny 1941).


Conference Wrap-up Miller

potentiallynegativeeffectsofsoilchangesonyield.Factorscontrollingyieldalsointeract.Forexample,soildisturbancemayreducevegetativecompetitionfortrees.Consequently, this indirecteffectof soildisturbanceoncompetingvegetationcanenhancetreegrowthorcompensatefordirect,potentiallynegativeeffectsofdisturbanceontreegrowth.

Whenyoupropose toharvest treesorprescribe fire,canyoupredict likelyconsequencesonsoilpropertiesandsubsequentplantyield?Thecomponentsof thispracticaland importantquestionaredisplayed in figure3.You,as theagent,proposetousegroundbasedequipmentatlocationY.Doyourecognizethateachlocationhasauniquecombinationofsoils,climate,andotherfactorsthatdeterminetheseverityofsoildisturbanceandthepracticalconsequencesfortreeorvegetativegrowth?Therefore,donotanticipatethesameeffectsonsoilorgrowthatalllocations.Refertocurrentresearchresultsandexplanations,forexample,Gomezandothers(2002);Powersandothers(2005)forjustificationofyourdecisionsandrememberyourA,B,C’s(fig.4).

Theconceptofecologicalstabilityalsoappliestosoilstability(fig.5).Soilsdifferintheirinitialresistancetoheavyequipmenttraffic.Forexample,comparevisualeffectsoftrafficonasandysoilcontaining70-to90-percentgravelandcobblesbyvolume in the top3 feetwith thatonadeepsilt loamsoil that isstone-free.Thesetwosoilsdifferintheirweight-bearingcapacityandinshearstrength,especiallywhenmoistorwet.Soilsalsodifferintheirresilienceorrateofrecoveryafterdisturbance.Rateofrecoveryofsoilpropertiesandfunctionsdependslargelyoninteractionsamongclimate,above-and-belowgroundorgan-isms,andsoilproperties.Forexample,recoveryishastenedinclimatesthatcausesoiltohavecyclesofthawingandfreezing,wettinganddrying,orclimatesthatpromoterapidgrowthofplantsandotherorganisms.

Figure 3—A general concept of actions and consequences.



Figure 4—Locations (sites) differ: Remember your A, B, C’s.

Figure 5—Ecological stability: response depends on resistance; recovery depends on resilience.


Conference Wrap-up Miller

Figure 6—Soils and site differ in resistance and resilience.

Amongthemanycombinationsofsoilsandmicro-andmacro-climatesintheInlandWest,weneedtoidentifyourA-,B-,C-locations.Recallasimilarurgingbyourafter-dinnerspeaker,LarryRoss:“goforthandstratifyforestland;”thenfitthepracticetothesoil.

Soilsandclimatesdiffer.Soilsandclimatesinteracttocreatevaryingconsequencesofsoildisturbanceorfireforyield(fig.6).Yourconsideringdifferencesinsoildepthlikedifferencesinbankaccountswillbehelpful:Equateshallowsoilstoa$100accountanddeepsoilstoa$1,000account.Thus,yourprescribingground-basedequipmentorfiretoreducefuelswillmostlikelyresultinreducedgrowthandsubsequentyieldonshallowsoilsorsoilswithshallowashcaps.Moreover,presenceofcoarse,non-weatheredrockfragmentsfurtherreduceeffectivesoildepthorthe“bankaccount.”Finally,rememberinteractions:whereequipmentorfiredegradesoilforplantgrowth,anticipatestrongerreductionsinplantgrowthwhereclimateisharshandlessfavorableforplantgrowth.

Final Take-Home Messages ______________________________________ 1.Donotassumenegative“consequences”forvegetationyieldonallsoils

andlocations(soilsdiffer…climatesdiffer…hence,treeresponsediffers). 2.HelpotherstoidentifyCaseA,B,Clocationsbymeasuringtreeresponse

todisturbance. 3.KnowyourA-,B-,C-soils/sites. 4.AllocatetimeanddollarsatCaseAlocations(whereactivitiesreducegrowth). 5.SavetimeanddollarsatCaseBandClocations(whereactivitieshaveno

effectorimprovegrowth). 6.Inshort,allocateyourprotectiveandrestorativeefforts…toachievefavor-

ablebenefit/costratios.



Literature Cited __________________________________________________Gomez,A.;Powers,R.F.;Singer,M.J.;Horwath,W.R.2002.Soilcompactioneffectsongrowth

ofyoungponderosapinefollowinglitterremovalinCalifornia’sSierraNevada.SoilSci.Am.J.66:1334-1343.

Jenny,H.1941.FactorsofSoilFormation.ASystemofQuantitativePedology.NewYork,NY:McGraw-Hill.

Powers,R.F.;Scott,D.A.;Sanchez,F.G.;Voldseth,R.A.;Page-Dumroese,D.;Elioff,J.D.;Stone,D.M.2005.TheNorthAmericanlong-termsoilproductivityexperiment:Findingsfromthefirstdecadeofresearch.ForestEcologyandManagement.20:31-50.

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The Rocky Mountain Research Station develops scientific information and technology to improve management, protection, and use of the forests and rangelands. Research is designed to meet the needs of National Forest managers, Federal and State agencies, public and private organizations, academic institutions, industry, and individuals.

Studies accelerate solutions to problems involving ecosystems, range, forests, water, recreation, fire, resource inventory, land reclamation, community sustainability, forest engineering technology, multiple use economics, wildlife and fish habitat, and forest insects and diseases. Studies are conducted cooperatively, and applications may be found worldwide.

Research LocationsFlagstaff, Arizona Reno, NevadaFort Collins, Colorado* Albuquerque, New MexicoBoise, Idaho Rapid City, South DakotaMoscow, Idaho Logan, UtahBozeman, Montana Ogden, UtahMissoula, Montana Provo, Utah

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volcanic-ash-derived forest soils of the inland northwest

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