ian pulsford, graeme l. worboys and dave darlington · 2020-05-04 · dave darlington, ba dip ed...

Revisiting Observations of Pest Horse Impacts in the Australian Alps, March 2020

Ian Pulsford, Graeme L. Worboys

and Dave Darlington

ThisreporthasbeenpreparedbyIanPulsford,GraemeL.WorboysandDaveDarlingtonandisavailableat:https://theaustralianalps.files.wordpress.com/2020/05/revisiting-pest-horse-impacts-to-australian-alps-catchments-2020.pdfImportantnoticeThissupplementary“Observations”reportisprovidedasanupdatetoareportbyWorboysandPulsfordin2013(Worboys,G.L.andPulsford,I.2013).ThisreportisproducedforgeneralinformationandisarecordofpersonalobservationsmadebytheauthorsfortheMtPilotareaofKosciuszkoNationalParkin2013thatwererevisitedinMarch2020.Ithasbeenpreparedwithinthecontextoftheauthorsparticipatingininspectionsofthisareaoveraperiodof47yearsfrom1973to2020andshouldbereadinconjunctionwiththe2013report.Responsibilityforthereportcontentsrestswiththeauthors.TheauthorswereaccompaniedontheirinspectionbyformerNSWEnvironmentMinisterandBoardChairdesignateoftheColongFoundationforWilderness,BobDebusAM.©Thereportisavailableforgeneraluse.Citation:Pulsford,I.,Worboys,G.L.andD.Darlington(2020).RevisitingObservationsofPestHorseImpactsintheAustralianAlps,March2020,Canberra.Availableat:Coverphoto:PhotoofaCowombatFlatferalhorseexclusionplotestablishedin1999,AlpineNationalParkVictoriashowinga21yearnongrazedareawithintheexclusionarea(photo-left)withallotherareasaccessibletoferalhorsegrazing,pugging,compressionanderosionofsoilanddestructionofnativevegetation,3Mar2020(Source:IanPulsford).

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Revisiting2013ObservationsofPestHorseImpactsintheAustralianAlpsinMarch2020Ian Pulsford, MSc.ProtectedAreaandLinkingLandscapesSpecialistandformerSenior Conservation Manager. Graeme L. Worboys, AM PhD Honorary Associate Professor, Fenner School, Australian National University Protected Area Management Specialist and former Senior Protected Area Manager. Dave Darlington, BA Dip Ed Environmental Science, former Senior Protected Area Manager. 28April2020INTRODUCTIONWemadeobservationsarisingfromaninspectionon22and23March2013oftheupperThredboRiverBigBoggy,CascadeCreek,IngegoodbeeRiver,TinMineCreekandMurrayRiverheadwatercatchments,KosciuszkoNationalPark(WorboysandPulsford2013).Weidentifiedunprecedented,pervasiveanddestructiveferalhorseimpactsforover43kilometresoftreelessdrainagelinesespeciallyinCommonwealth-listedAlpineSphagnumBogsandAssociatedFensEndangeredEcologicalCommunitieswhichoccurinthehighheadwatercatchmentsoftheAustralianAlps.Wereportedthat“theseimpactsweretheworsteverobservedin40yearsofpersonalinspectionsoftheDeadHorseGaptoTinMinessectionofthePilotWildernessofKosciuszkoNationalParkinNewSouthWalesandatCowombatFlatareaoftheVictorianAlpineNationalPark.BothoftheseparksformpartoftheAustralianAlpsnationalparks”.On3and4March2020werepeatedourobservationsofmanyofthesamesitestoevaluateifanychangesinimpactshadoccurredsinceourlastvisit7yearsago.Ourconclusionisthattheconditionofwetlandbogsoncreekflatsandcreekbanksintreelessdrainagelineshascontinuedtodeteriorateduetothecontinuedpresenceoflargeferalhorsepopulations.Sinceourlastobservationsin2013feralhorsepopulationmanagementceasedin2015inthePilotareaand99horseswereremovedfromBlueWaterHolesinthespringof2019inthenorthernendofthePark(DPIE2019).Inaddition,therehasbeenarecentrapidincreaseinpopulationsofdeeraswellassomepigsthatwererecordedbytheNPWSduringaerialsurveys(Cairns2019,NPWS2019).WehadintendedtoalsorevisitsitesalongandneartheIngeegoodbeeTrail,howeverthiswasnotpossibleduetointroductionofCOVID-19travelrestrictions.Wesawnoevidenceofrecoveryatthesiteswerevisitedandinmanyareasdamagetowetlandsandbogsalongriverflatsweremoreextensive.Conditionsweremuchdrierthanduringour2013inspectionduetotheprolongedseveredrought.Theareaswerevisitedwerenotdirectlyaffectedbythemega-firesthatburntlargeareasofeasternAustraliainJanuaryandFebruary2020.However,partsofthenearbywesternfalloftheupperMurrayandGeehiRiversandslopesofthewesternfalloftheKosciuszkoMainRangeuptoDeadHorseGapontheAlpineWaywereseverelyburnt.

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HORSEPOPULATIONESTIMATESSinceourfirstobservationsoverthelast40yearsandour2013reportofferalhorsesimpactsinthePilotWildernessAreasouthofThredbo(WorboysandPulsford2013),horsepopulationshavecontinuedtoincreasesubstantiallyinmanyareasoftheAustralianAlps.In1990researcherJennyDyringmadepopulationestimatesofseveralhundredhorsesintheBigBoggy,CascadesCreek,IngeegoodbeeRiverandCowombatFlatareasouthofThredbo(Dyring1990).MichelleDawsonneeWalterconductedanaerialsurveyin2001(Walter2002)thatestimatedpopulationsof2horsespersquarekilometreintheBigBoggyand6.4horsespersquarekilometreintheCowombatpopulationof(Dawson2005).

AerialsurveysintheAustralianAlpsnationalparksestimatedapopulationof5,200in2001;2,369in2003;and7,679horsesin2009,a21.65%perannumincreasesincethepreviousestimatein2003(Dawson2009).InApril-May2014andApril-May2019theNSWNationalParksandWildlifeService(NPWS)conductedrepeatsystematicaerialsurveysacrossthreeblockscoveringtheentiredistributionofferalhorsesintheAustralianAlps(KosciuszkoNationalParkandadjacentstateforestareasinNewSouthWalesandtheAlpineandSnowyRiverNationalParksinVictoria).ThesesurveysweredesignedandanalyzedbyStuartCairns.Thehorsepopulationsincreasedintheseblocksfrom9,187in2014to25,318in2019,anaverageincreaseof23%perannum(Cairns2019),(Figure1).ThepopulationintheByadbo-Victoria(SnowyRiverandAlpineNationalPark)surveyblock,whichincludedthePilotWildernessarea,increasedby15%from4,316to8,518(Cairns2019).Otherlargeintroducedherbivoresincludingdeer,cattle,goatsandpigswerealsoobservedduringtheseaerialsurveys.Themostnumerousoftheseotherspeciessightedwereintroduceddeer.In2014theestimatedpopulationofdeerwas2,280whichincreasedto7,630in2019.Thisequatedtoanannualrateofpopulationincreaseinthedeerpopulationof27%.ThisrateofincreasewasmuchhigherthantherateofincreaseforthehorsepopulationinByadbo-Victorianblock.Populationestimateresultsfromtheseaerialsurveysindicatethathorsepopulationsstillexceedferaldeerpopulationswithinthesurveyblock.Thesurveysalsorecordedgoatsandpigsbuttheywerefarlessnumerousandwerenotobservedinnumbersthatallowedanalysistoprovidestatisticallyrobustpopulationestimates(Cairns2019).

Atthetimeofourlastvisittotheareain2013theNPWSconductedongoinglimitedcaptureandremovalofwildhorsesfromthearea.RemovalofhorsesfromthePilotWildernessareain2015ceasedpriortocommencementofcommunityconsultationandexhibitionofthedraftKosciuszkoWildHorseManagementPlanin2016(OEH2016).In201999horseswereremovedfromtheBlueWaterHolesareainthenorthernsectionoftheParkafterthecommencementoftheKosciuszkoWildHorseHeritageAct2018(R.Gibbspers.comm.).TheNPWSalsoconductedaseparateseriesof9aerialsurveysbetween2006and2019toestimatethenumberofhorsesin3,500haofsubalpineecosystemsintheBigBoggyareaofthePilotWildernesssouthofThredbo(Figure2).TheMay2019surveyrecorded202horsesNinerepeatsurveyscarriedoutatthesametimeofyearfrom2006to2019indicatedthatthepopulationdensityhasincreasedfrom2.7to6.28horses/km2respectively(NPWS2019).TheMtPilot–CascadesCreekandTinMinesareathatweinvestigatediscontiguouswiththeupperThredboRiver“BigBoggy”andconsistsofsubalpinewoodland,treelessdrainagelinesandmontaneforestsonthewatershedoftheGreatDividingRange.

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Figure1HorsepopulationestimatesintheAustralianAlps,2001-2009(afterDawson2009)and2014-2019(afterCairns2019).SeeDawson2009andCairns2019forsurveydesignandrespectiveareassampled.

Figure2.Comparisonofhorsestrappedandremovedfromsurveyareaandpopulationestimatesfromannualaerialsurveysinthe3,500haupperThredboRiver“BigBoggy”studyareasouthofThredbo(afterNPWS2019).

Horsesremoved Horsepopulationestimatebasedonaerialsurveys

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VEGETATIONDESTRUCTIONIn2013wereportedthatexcessivenumbersofpesthorseswereobservedtobedirectlydestroyingsubalpinenativevegetationandthiswasbestillustratedin2013atexclosureplotsestablishedatCowombatFlatAlpineNationalParkin1999.Thesefourexclosuresare21yearsoldandarelocatedintheupperheadwaterstreamofAustralia’slongestandmosteconomicallyimportantriver,theMurray,justafewkilometresfromitssource.Theimpactswerevisuallyveryclearin2013andtheimagesbelowdemonstratethattheconditionofthevegetationhascontinuedtodeclineasaresultofgrazingbylargenumbersofhorsesanddeeranddrought.Weobservedrelativelylittledisturbancebypigs.Astudyofimpactsofherbivoregrazinginnearbylowerelevationwhitecypresspine–whiteboxcommunitiesalongthelowerSnowyRiverValleywithinthePilotWildernesswasinvestigatedbyJessicaWard-Jonesandcolleaguesin2018.In2013and2017/2018fencedexclosureandpairedgrazedplotswhichhadbeenconstructed1984weresurveyedtoassesstheseverityofimpactsonvegetation,soilandinvertebratesusingarangeoftechniquesincludingLandscapeFunctionAnalysis.Dungcountsconductedin1987and2018wereusedtoassesstherelativepresenceofherbivores.Therewasfourtimesmoredungrecordedin2018thanin1987(totaldryweight).Horseanddeerdungwasabsentin1987,butdominatedin2018.Dungtransectdatacollectedinthegrazedplotsandadjacentgrazedlandscapeshowedthat84%ofdungwasfromhorses,13%fromdeer,2%frommacropodsand1%fromrabbits.Theherbivoreexclusionplots,fencedfor34years,exhibitedsignificantlyhighersoilandvegetationconditionthanthegrazedplots,aswellasinvertebrateabundance.Vegetation structureandcomposition,andsoilstabilityandfunctionwithintheplotswasimproving, whereassoilsoutsidetheplotswerebareanderodinginbroadsheetsacrossslopesandingullies.Densenetworksoftracksandtrampingbyhorsesweremostevidentwithdamagetosteepcreekbankscausedbydeer(Ward-Jonesetal.2019).

In2015themostextensivestudytoassesstheimpactsofhorsesthroughoutpubliclandintheAustralianAlpswasundertakenbyRobertsonetal.(2015).Theirstudydemonstratedthatferalhorsesarehavingasignificantimpactontheconditionofdrainagelinesacrossthisrange.Almostallsitesassessedwithinthebroadhorsedistributionshowedevidenceofhorsepresence,andallofthesitesinpoorestconditionwereoccupiedbyhorses.Theyfoundthatonaverage,about28metresofthestreambedineach50msitetheymeasuredhadamoderatetohighsedimentloadinhorsepresentsites,comparedtohorsefreesiteswherebankswerestableduetothepresenceofundisturbedfringingvegetation.Theyconcludedthelossofstability,modificationofstreambanksandvegetationstructurehavesignificantimpactsontheconservationoffaunaincludingarangeoflistedthreatenedandotherspeciesincludingAlpineBogSkinkPseudemoiacryodroma,AlpineShe-oakSkinkCyclodomorphuspraealtusandAlpineTreeFrogLitoriaverreauxiialpina.Asaconsequencethishasledtothelistingof“DegradationandlossofhabitatscausedbyferalHorses(Equuscaballus)”asapotentiallythreateningprocessundertheVictorianFloraandFaunaGuaranteeAct1988.On30Nov2018theNSWThreatenedSpeciesScientificCommitteelisted“habitatdegradationandlossbyFeralHorses(brumbies,wildhorses)”asakeythreateningprocessundertheNSWBiodiversityConservationAct,2016.

ConsistentwithourownobservationsintheMtPilotarea,Robertsonetal.(2015)concludedthatthemostcriticalimpactofferalhorsesintheAlpsisthedamagetheycausetoAlpine

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SphagnumBogsandAssociatedFensalongtreelessdrainagelines.ThisisanendangeredecologicalcommunitylistedundertheCommonwealthEnvironmentProtectionandBiodiversityConservationAct1999.Wefoundthatthatthesehabitatshavecontinuedtodeclinetoanalarmingdegree.Thishighlyendangeredcommunityprovideshabitatcriticalforthepreservationofendangeredspeciesandaswellasimportantlyfilteringlargequantitiesofcleanwaterwhichisreleasedslowlyintostreamsenhancingcatchmentvalueandpreventingsoilerosion.Seephotosbelow.ThephotographsbelowclearlyillustratetheextentofthedamagetonativevegetationalongtreelessdrainagelinesoftheupperThredboRiverBigBoggy,CascadeCreek,IngegoodbeeRiver,TinMineCreekandMurrayRiverheadwatercatchments,KosciuszkoNationalParkfromferalhorses.

Figure3.LocationofobservationsintheMtPilotareaofKosciuszkoNationalParkandAlpineNationalParkintheAustralianAlps22and23March2020.(Source:GoogleMaps:TerraMetrics2020Imagery).

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Horseimpactedvegetationsurroundinga1999exclosureplotwithitsprotectedswardofsedgesandgrasses,CowombatFlat,VictorianAlpineNationalPark,neartheNSWborder,23March2013(Source:GraemeL.Worboys).

Horseimpactedvegetationsurroundingexposingbaretrampledandcompactedsoilatthesameexclosurethatwasconstructedin1999withitsprotectedswardofsedgesandgrasses,CowombatFlat,VictorianAlpineNationalPark,VictorianAlpineNationalPark,3March2020(Source:IanPulsford).

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Exclosureplotfenceconstructedin1999withprotected(left)andunprotectedsedgeandgrassvegetation,CowombatFlat,VictorianAlpineNationalPark,23March2013.(Source:GraemeL.Worboys).

Exclosureplotfenceconstructedin1999withprotected(left)andunprotectedsedgeandgrasswetland,CowombatFlat,VictorianAlpineNationalPark,3March2020(Source:IanPulsford).

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MurrayRiverheadwaterstreamimpactedbyhorsesasitemergesfromdenseprotectedswardofsedgesandgrasseshabitatwithina1999exclusionplotatCowombatFlat,March232013.(Source:IanPulsford).

MurrayRiverheadwatersstreamimpactedbyhorsesasitemergesfromdenseprotectedswardofsedgesandgrasseswithinanexclusionplotconstructedin1999atCowombatFlatinAlpineNationalPark.Notecompaction,bankdisturbanceanderosionhaveincreased,vegetationcoverislowerandvegetationstructureislesscomplexthaninsidethesameexclosures,3March2020.GrazingimpactsattheseplotshavebeendescribedbyProberandThiele(2007)andWildandPoll(2012)(Source:IanPulsford).

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Horsetramplingimpactstostreambanksandstreambankcollapse,headwatersoftheIngeegoodbeeRivernearTinMinesHut,KosciuszkoNationalPark,22March2013(Source:GraemeL.Worboys).

Horsetramplingimpactstothesamestreambanks,headwatersoftheIngeegoodbeeRivernearTinMinesHut,KosciuszkoNationalPark,3March2020(Source:IanPulsford).

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Horsetramplingincisionofstreambanksandbankcollapse,headwatersoftheIngeegoodbeeRivernearTinMines(Carters)Hut,KosciuszkoNationalPark,23March2013(Source:GraemeL.Worboys).

Horsetramplingandincisionofstreambankscausingbankcollapse,headwatersoftheIngeegoodbeeRivernearTinMines(Carters)Hut,KosciuszkoNationalPark,3March2020(Source:IanPulsford).

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FormersubalpineriparianbogtrampledandtransformedintoalargemudpanbyhorsesintheupperheadwatersoftheIngeegoodbeeRiver,23March2013(Source:IanPulsford).Wewereunabletorevisitthissiteduetoheavyrain.

TramplingimpactstoasubalpinebognearTinMinesHut,KosciuszkoNationalPark,23March2013(Source:GraemeL.Worboys).

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TramplingimpactstoaformerwetheathandsubalpinebogbetweenCascadesHutandTinMinesHut,KosciuszkoNationalPark,22March2013(Source:GraemeL.Worboys).

TramplingimpactstothesamesiteofsubalpineboganwetheathandbetweenCascadesHutandTinMines(Carters)Hut,KosciuszkoNationalPark,3March2020(Source:IanPulsford).

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TramplingimpactstoawetlandbogatTinMinesHut,KosciuszkoNationalPark,23March2013withremnantsoilpedestal(Source:IanPulsford).

TramplingandpuggingimpactsbyhorsestoawetlandbognearTinMines(Carters)Hutsurroundedbycompactedcloselycroppedgrasses,KosciuszkoNationalPark,4March2020withremnantgrassycoveredsoilpedestal,centre.(Source:IanPulsford).

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Horsedustbath,CowombatFlat,Victoria,100metressouthandeastoftheNSWborder.Notehardcompactedgroundandveryshort-croppedgrassesduetograzingbyhorses,23March2013.(Source:GraemeL.Worboys).

ThepuggedandbrokenedgesofthebanksoftheupperMurrayRiverheadwaterstreamformamuddyerodingpooltrampledbyhorsesnearitsheadwaters.Thisisthesamepoolseenintheabovephoto.CowombatFlat,Victoria30metressouthandeastoftheNSWborder,3March2020.(Source:IanPulsford).

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Horsestrampling,trackingandgrazingthroughshrubbywetheathandsphagnumbogneartheCascadeFireTrail1.5kmsouthwestoftheupperThredboRiver.Notethehorsetracksthroughoutthedissectedvegetation,3March2020(Source:IanPulsford).

SmallSphagnumandCarexbogdestroyedbyhorsestrampingandgrazingexposingandpuggingpeatandsoil,CascadeCreekflatsnearCascadeFiretrail,3March2020(Source:IanPulsford)

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SmallSphagnumandCarexbogdestroyedbyhorsestrampingandgrazingexposingandpuggingpeatandsoil,CascadeCreekflatsnearCascadeFiretrail,3March2020.(Source:IanPulsford).

SubalpinebogSpreadingRopeRushEmpodismaminusandSphagnumMossSphagnumcristatumhummock(foregroundright)andsurroundinghabitatdestroyedbyhorsestrampingandgrazinginadrainagelinenearTinMines(CartersHut),3March2020.(Source:IanPulsford).

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LargeareaofcompactedhardpansoilsurfacewhichwasonceasphagnummossbogthathasbeendestroyedbytrampingandgrazingsouthwestofTinMines(Carters)HutonthecrestoftheGreatDivide.WetlandsheredrainintoeithertheMurrayRiverorSnowyRiver.Therearemanylargebarepatcheslikethisalongheadwatersandcreekflatsinthisarea,4March2020(Source:IanPulsford).

Horsedungpileson“mowed”snowgrassesandboggyvegetation(background)destroyedbyhorsegrazingandtramplingsouthwestofTinMines(Carters)Hut,4March2020(Source:IanPulsford).

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Hardcompactedvegetation(left)comparedtoBogSnow-grassPoacostinianathatwasprotectedfromgrazingbyhorsesbyanexclosurefenceconstructedbytheNPWSinNov2011(R.Gibbspers.comm.)southwestofTinMines(Carters)Hut.Notethestripwithintheexclosuregrazedbyhorsesreachingintotheplot,4March2020(Source:IanPulsford).

A1.8mtallhummockofSpreadingRope-rushEmpodismaminus,MountainCord-rushBaloskionaustraleandSphagnumMoss(Sphagnumcristatum)protectedfromgrazinginsideanothersectionofthesameexclosuresouthwestofTinMines(Carters)Hut.TheexclosurefencewasconstructedinNov2011providesimportantevidenceofthealmostcompletelossofsubalpinesphagnumbogvegetationoutsidetheplotandwhichhasoccurredalongsubalpinecreeklinesintheareaduetograzingandtramplingmostlybyhorsesandthemorerecentlyreportedincreaseindeerpopulations,4March2020(Source:IanPulsford).

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CONCLUSIONSWildhorsesanddeerspeciespopulationsonsurveyedareasofpubliclandsintheAustralianAlpshavegrownrapidlysince2013(Cairns2019)duetoacombinationoffactorsincluding:(1)naturalpopulationincrease(2)lackofnaturalpredatorsordiseases,(3)cessationofhorsecontroloperationsin2015andonlylimitedcontrolofrapidlyincreasingdeerpopulationsinmanysurveyedareassince2015.Thisisinspiteofthreeyearsofrecorddrought.HoweverdroughtwasclearlywaslesssevereintheMtPilotareathanelsewhereineasternAustraliaduetoitsrelativelyhighelevation,ruggedness,coolerandmoisterconditions.Uncontrolledandincreasingnumbersofwildhorsesanddeerhavereachedrecordlevels.Asaconsequencetheconditionsoftreelessdrainagelineareasthatweobservedin2013havecontinuedtodecline.Weobservedthatthegrowthinhorsepopulationandthemorerecentlyobservedrapidincreaseindeerpopulationsanddroughthaveallcontributedtothefurthercontinuingdeclineincatchmentcondition.Wesawnowetlandhabitatsintreelessdrainagelinesthatexhibitedsignsofrecoverysinceourlastobservationin2013.Anyrecoveryofcatchmentconditionisnotpossibleuntileffectivelong-termmeasuresareimplementedtoremoveorverysignificantlyreducethenumbersofpestspeciesespeciallyhorsesanddeer.Thedamagingimpactsofstockgrazing,whichwasendedbythethreevisionarypolicydecisionsbygovernmentandgreatleaderswhichbannedgrazingin1944,1957and1969(Costin2018)hasbeenreplacedbytheuncontrolledgrowthofwildhorse(Driscolletal.2019)andrecentrapidexpansionofdeerpopulations.BasedontheresearchbyWimbushandCostin(1979)ontherecoveryofsubalpinevegetationfromimpactsofgrazing,evenifhorseanddeernumbersareverysignificantlyreduced,itwilltakealongtimeforthesecommunitiestorecoverandmanyoftheseplantcommunitiesmayremaininasub-climaxstateafterinitialrecovery.Rehabilitationworkisurgentlyneeded.Thiscannotcommenceuntilintroducedherbivorepopulationsareremovedorsignificantlyreduced.InthemeantimetheconditionoftheheadwatercatchmentsofAustralia’smosteconomicallyimportantriversthatprovidewatervitalforirrigationandelectricitywillcontinuetodegrade.________________EndNoteTheauthorshavethehighestregardforhorsesandappreciateandsupporttheirplaceinmostareasofAustraliasuchasfarms,townsandsportingtracks.Weunderstand,appreciateandsharethedelightandcompanionshiphorsesbringtomanypeople.Thisreportisnotanattackonhorsesperse.Rather,itisaboutraisingawarenessoftoomanyhorsesandtheunacceptableandexcessiveimpactsinoneofAustralia’smostimportantconservationareas,theAustralianAlpsnationalparks.Acknowledgements.WewishtoexpressourappreciationtothefollowingNPWSstaff:MickPettitandPamO’Brienforapprovaltoconductthefield-work;RobGibbsforadviceabouthorsepopulationsurveysandconstructionoftheplots;andGenevieveWrightforplantidentification.

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SubalpinebogonCascadeCreekgrazedandtrampledmostlyhorses,650mnorthofCascadeHut,3March2020.(SourceIanPulsford).