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Environmental ReviewA Monthly Newsletter of Environmental Science and Politics

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In the summer of 1988 a series offorest fires burned a million acres inand around Yellowstone NationalPark — about one half of the ecosys-tem — and the Park Service wascriticized for letting such a disasterhappen. Some critics argued that thepark "let it burn" policy whichallowed natural wildfires to burn ifthey didn’t threaten human settle-ments, led up to the massive fires of1988. They also argue that intentionalburning as it is practiced in othertypes of forests to reduce fuel loadswould have avoided the burnedforests, dead wildlife, massive soilerosion, property damage, and airpollution the fires caused. BillWattenburg, a radio personality, in aletter to Science referred toYellowstone as a “vast cemetery ofburned, rotting, and bug infested treestumps that is all that remains of880,000 acres of once beautifulYellowstone forests...”

However, scientists who havestudied the Yellowstone ecosystembefore and after the great fires saythat prescribed burning, although itmay reduce wildfires in other kinds offorest, is unworkable in Yellowstone.The historical fire regime inYellowstone was characterized byinfrequent but very intense fires.While the 1988 fires were unprec-edented in modern times, such fireshave occurred pretty regularly every

few hundred years, and theYellowstone ecosystem was notpermanently damaged by the fires.

We spoke with two scientistswho have worked on different aspectsof Yellowstone ecology about theirwork before and after the great fires,Linda Wallace, a grasslands ecolo-gist, and Grant Meyer a geologistwho has studied fire-related soilerosion. We asked them to give ustheir perspective on the 1988 fires.

ER: Professor Wallace, what is yourtraining?

LW: I received my Ph.D. in botanyfrom the University of Georgia, afterwhich I did a post-doc at SyracuseUniversity studying grasslandecology in the Serengeti. Then I got ajob here at the University of Okla-homa in 1981, which is the perfectplace to study grassland ecology. Mywork focuses on grassland ecologyand plant-animal interactions,particularly how grazers affectgrasses.

ER: I thought of the park as mostlyforest.

LW: It is. You can divide the parkinto two main categories, high andlow elevation. The majority of thepark, perhaps three-quarters of it ishigh elevation subalpine plateau. Thisis the southern part of the park and itis mostly forested. The lower eleva-tion part of the park — the northernpart — is where the grasslands are,and this is the winter range forgrazers like the elk, deer, bison. Thelow elevation area runs along theLamar Valley and YellowstoneRivers and follows the northerncourses of those rivers.

The largest expanses of grass-lands are in the northern part of thepark which has the richest soils. Thenorthern part of the park has rich soiland the southern part of the park hasextremely poor soil. In the southernpart of the park there are practicallyno nutrients in the soils in some areas,it’s like trying to grow plants onwashed sand. So as a consequence,

Volume Six Number Five May 1999

CONTENTS:

WHY DIDYELLOWSTONE

BURN?LINDA WALLACE &

GRANT MYER

GLOBAL WARMINGAND CHANGES IN

PLANT COMMUNITYSTRUCTURE:

RICHARD ALWARD

2

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you’ll see the trees, the lodgepolepine and the other cone bearing treesin these nutrient-poor habitats, whilethe grasslands are going to be foundin the richer soils. That is not to saythat the southern part of the park isone giant monotonous forest though,because there are pockets of deep soiland meadows, but those meadows aremuch smaller than those in thenorthern part of the park.

ER: The suggestion in Wattenberg’sletter is that controlled burning before1988 would have prevented the worstof the big fires. What is your opinionof that?

LW: Many people have stated that asa big concern, that the no burn policyallowed the fuel loads in the woods toget so high that a catastrophic fire like1988 was bound to happen. There area couple different arguments whythat’s probably not the case. One,there’s historical evidence that bigfires have happened naturally in thepast before humans ever got in thereand started fighting fires. The otherthing to think about is, How effectivehas fire fighting been? The southernpart of the park is rugged terrain, veryremote, and fire fighting effortsbefore the policy was adopted in 1972were not very effective. In thesouthern part of the park whateverfuel was there is pretty much naturalbecause the fires just weren’t put out.Fire fighting was probably moreeffective in the northern part of thepark, even though it has a higher firefrequency than the southern part ofthe park because it’s lower elevation

and it’s drier. Its natural fire fre-quency is about once every twenty-five years; while the frequency of bigfires for the southern part of the parkis on the order of hundreds of years.Bill Romme has looked at fire historyin the park in recent ecological timesand has found that large-scale firesseem to happen every few hundredyears or so. So this is nothing new,this is the ecosystem resetting theclock and starting anew.

ER: How did you get involved inYellowstone and the fires?

LW: In 1988 I was taking a sabbati-cal leave in Yellowstone where I wasstudying how the native grazersaffected the grasslands. The big firesoccurred that summer so I startedincorporating fire research into mygrazing research. But back in 1985 anumber of people were voicingconcern that the park was being overgrazed and there was a congressionalmandate that research be done in thepark to address that issue, by non-Park Service scientists. So the parkasked a number of people to come inand do research; I was one of thosepeople.

With four or five people doingresearch on the grasslands usingdifferent techniques, we all came upwith similar results: the grasslands inthe park were not being over grazed.The grasslands in the park evolved inthe presence of high levels of grazing,particularly in the summer range, andthey can tolerate the high levels ofgrazing that they are experiencingnow.

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ER: How do you explain that tovisitors who see unsightly, damagedmeadows in the park?

LW: In the winter range the plantsare not typically grazed during thesummer growing season; they aregrazed in the winter time when thegrasses are dormant. One of theproblems the park has faced is that

Volume Six Number FiveMay 1999

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the winter range is quite visible to thepublic. Many of the roads in the parkgo through the winter range, andwhen the snow melts off, people see abarren, devastated landscape becausethe animals have eaten away the deadvegetation before the new vegetationcomes up. So for a period of about amonth in the early spring the winterrange looks pretty bad, but in reality itis not that terrible.

The animals, the elk and deer,come down from the summerrange in the fall and then over thewinter they’re eating this driedvegetation. While they are on thewinter range they of coursedefecate and urinate, and in thatprocess they are transferring plantnutrients from the summer rangeinto the winter range. Severalresearchers have looked at thisand have found that in thesegrazed winter habitats there aremore nutrients and the nutrientsare cycling faster when theanimals are present.

ER: Why did the Park Servicehave to bring in outside scientists?

LW: There were a number ofvocal park opponents; for them,no matter what the park does it’swrong. So the only way to satisfythe worries of these people was tosay, OK, we’ll have people whoaren’t associated with the park do theresearch.

ER: Is this an academic controversy?

LW: Oh, no. It’s a big politicalcontroversy. Would that it wereacademic. Yellowstone is the world’sfirst national park, so everything thatYellowstone does is politically

interesting. Yellowstone has been in afish bowl ever since it was created.There’s a great deal of interest inYellowstone and anything thathappens in the park attracts publicattention.

ER: What caused the 1988 forestfires to be so big?

LW: When the fires of 1988 started,

that was a unique set of climatologi-cal circumstances. Preceding 1988there had been a number of years ofmild winters and wet summers. As aconsequence of that the elk mortalityhad been low and there was a largebuild-up of forage for them; and infire language forage — grasses andforbs — translates to fine fuels. Sothe stage for some big fires was set bythe unusual climatic circumstances

that preceded 1988: a large build-upof fine fuels.

Since 1972 the park had the let itburn policy which basically statesthat in the park, if there is a fire ofnatural origin and it is not threateninghuman habitation structures or life orany unique natural area, it will beallowed to burn, but it will bewatched carefully. Since 1972 mostof the fires were small, they might

burn one to ten acres, but nothingbig. That was the normal situa-tion. So in 1988 with the let it burnpolicy still in effect, the first bigfire started early in the summer upin the northwest corner of the park— it was called the Fan fire — itstarted burning towards privateland owned by the Church Univer-sal and Triumphant, so the parkput that fire out.

Then there were somelightening-caused fires and asthey grew in size, the park real-ized it was going to be a bad fireyear and they started fighting allof the fires, and they fought themwith everything they could throwat them. But the weather was suchthat there was nothing peoplecould do to stop those fires. Thiswas a different part of the contro-versy. Many critics of the parksaid they should have put the firesout. But there was no way they

could have.During the fires that summer, a

hurricane came inland on the Texasshore down by Corpus Christi, andpeople were talking tongue in cheekabout the let it blow policy; that is, weshould stop this hurricane fromharming the national seashore. Thepoint being, putting out these fireswas in the same category as stoppinga hurricane. There was no way it

In1988 fires burned over a millionIn1988 fires burned over a millionIn1988 fires burned over a millionIn1988 fires burned over a millionIn1988 fires burned over a millionacres of Yellowstone Park and theacres of Yellowstone Park and theacres of Yellowstone Park and theacres of Yellowstone Park and theacres of Yellowstone Park and thegreater ecosystem.greater ecosystem.greater ecosystem.greater ecosystem.greater ecosystem.


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could feasiblely be done. The ParkService and various other entitiesspent over 120 million dollars, andthere were at one point 10,000 firefighters in the park. Finally in Sep-tember a quarter of inch of snow putthose fires out.

ER: So it wasn’t for lack of trying.

LW: No, it certainly wasn’t for lackof trying, but that controversy stillexists. After the fires another contro-versy erupted saying that we neededto start replanting all of these burnedareas; we needed to go in and startseeding grasses to prevent soilerosion.

There have been a number ofstudies done on that and people havefound instudy afterstudy thatwhen you gointo a re-cently burnedforest areaand startplantinggrasses andflowers, youslow succes-sion. The trees are going to be theclimax stage of succession there andas seedlings they have a hard timecompeting with the herbaceousvegetation that is planted. So the ParkService decided not to do that; theForest Service did some seeding onsome areas, and you can go to thoseareas now and see that there are notthat many trees there even after tenyears.

On the deep soils is where you’llfind the grasses, and the shallowrocky soils are where you’ll find thetrees. Tree seedlings do not growrapidly, and they don’t compete well

with the faster growing grasses andforbs, so trees grow in more severehabitats where they can successfullycompete and get established. It makessense to just let things revegetatethemselves and let everybody sortthemselves out as to where they’regoing to live.

ER: Has Yellowstone been alteredmuch or is it more or less pristine?

LW: Despite the millions of peoplethat visit Yellowstone every year,Yellowstone is a pretty big place —2.2 million acres — most of thehuman effects are localized rightalong the roads. A large proportion ofvisitors will only drive in, get out ofthe car to go see some of the thermalareas, maybe stop and get out of the

car to take a picture of some elk andbison, and go on their way. The backcountry of Yellowstone is the vastmajority of Yellowstone, it is veryslightly affected by people and it’sclose to pristine habitat. Unfortu-nately, many exotic plant specieshave blown in, so we can’t say it’sabsolutely pristine, but it’s close tooperating on nature’s terms.

ER: Wasn't controlling soil erosionthe reason for reseeding burnedareas?

LW: One of the things that the writerof the letter to Science was concernedabout was erosion because manyslopes have less vegetation on themafter the fires, and this is highlyerodible soil. But erosion is also animportant mechanism for gettingnutrients into the aquatic system. It’sa way to form new gravel beds, whichare important for willows and cotton-woods and for fish spawning. Erosionis how these things get put into thesystem. We tend to think of erosion asbad because humans usually acceler-ate it and then things get out ofcontrol, but we have to differentiatebetween natural levels of erosion anddisturbed levels of erosion. [GrantMyer talks about fire-related soilerosion in more detail in the follow-ing interview. Ed]

ER: He calledYellowstone a vastcemetery of deadtrees.

LW: There is lots ofdead wood in the parkbut also there’s a lot oftree seedlings coming

up in the midst of that. In a cold, dryecosystem like Yellowstone, plantnutrients become available in thesoils slowly, so the plants are adaptedto scrounging up small amounts ofnutrients as they become available. Ifa lot of nutrients became available allat once, the plant community prob-ably couldn’t take up much of themand a lot of those nutrients would getflushed through the system.

Dead trees and logs and stumpsact like nutrient sponges in that theyrelease nutrients slowly over time. Sothe dead logs and the dead trees have

Bill Romme has looked at fire history in the park ingeological times and has found that large-scale firesseem to happen every few hundred years or so. This isnothing new, this is the ecosystem resetting the clockand starting anew.


5


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an important role to play in thissystem: they release nutrients at a rateat which the plant community cantake them up.

They are also important sites forother species. Wattenburg said thelogs and snags were bug infested.Well yes, there are bugs up there, anda lot of those are important bugs.They are a part of the ecosystem justlike everybody else. They are not thebig brown-eyed charismaticmegafauna, but they are importantspecies there nonetheless. They serveas food sources for other animalsincluding some of the charismaticmegafauna. The bears love to rip intologs and eat the bugs that live inthere.

Dead trees are also an importantcomponent of the ecosystem.People were saying they needed tocome in and salvage that timber. Thatwould have been a big mistakebecause the nutrients those logsrepresent would have been hauledoff, making an even harsher environ-ment for the next generation of treesto come up. And we would have beenlosing those bugs, which are impor-tant for other members of thatecosystem. We would have beenaltering the food chain a lot.Right after the fires had stopped therewas an effort by the Park Service todeal with what they thought werehazard trees. Some of these treeslooked like they were going to falldown if you just sneezed in theirimmediate vicinity, and they wereworried that these could fall onvisitors or their cars, which is alegitimate concern. Well, the com-pany that they hired to do this got alittle carried away working on theroad between North and Madison,and also on the road between Mam-

moth and North. Some of thosehazard trees would have had to jumpuphill quite a ways to hit somebody.

ER: Where do the elk and deer fitinto the recovery from the fires? Didthat make for some hard years forthem?

LW: Before the fires there had beenseveral mild winters and we hadmany animals in the park that wereolder than they would have normallybeen. The winter following the fireswas a normal winter up there; andwhat’s normal for Yellowstone is apretty rough winter, so many animalsdied the year after the fires. It wasn’tso much because of the fires as it wasthe severe winter. Many animals hadoutlived their normal life spansbecause of the previous mild winters,and so many animals died that winter.People were saying it was because ofthe fires, and they wantedYellowstone to feed the animals likethey do down in Jackson Hole. ThePark Service did not do that. Onereason being that when you put thesewild animals in feed yard situations,you get better conditions for thetransmission of diseases. It wasdecided it would be better to let theseanimals disperse across the landscapeand make it or not make it.

Dead animals are also an impor-tant component of the system. They

were important for coyote popula-tions and other carnivores. When thegrizzly bears came out of hibernationthat next spring, they had goodpickings. That winter, the elk left thepark in droves. That season was aboutthe highest tag success for the earlyand late elk hunt that they had everseen. So there were many animalsthat left the park and got killed in thehunt.

Some critics of the park werearguing there is a correlation betweenthe fire and ungulate survival. But,two different computer models builtby separate labs coming at theproblem in different ways, came upwith the same answer: ungulatemortality was more due to the sever-ity of the winter than the fires. Lastwinter, 1997-98, was a severe winter,it was not even normal, it was severe,and again we saw high levels ofungulate mortality. And there wereno big fires in Yellowstone lastsummer.

ER: Is there a role for controlledburning in Yellowstone?

LW: I don’t think prescribed burningwill preclude one of these big firesfrom ever happening again. Pre-scribed burning might be good toprotect human developments, but asfar as saying we’re going to managethe whole 2.2 million acres of the


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Effects of the 1988Effects of the 1988Effects of the 1988Effects of the 1988Effects of the 1988Yellowstone Fires on theYellowstone Fires on theYellowstone Fires on theYellowstone Fires on theYellowstone Fires on theLandLandLandLandLand

Introduction:

One of the more spectacularresults of the 1988 fires inYellowstone was soil erosion: thedumping of mud, gravel, boulders,and trees into mountain streams.Fires burned the vegetation whichholds the soils in place and the falland winter rains washed tons oftopsoil and debris into the streams.Fires of this magnitude occur in theYellowstone ecosystem every fewhundred years, more frequentlyduring warm climates such as theMedieval Warm Period about 1000A.D., and less freqently duringcolder climates, such as the Little IceAge around 1300 A.D. The geologi-

cal record, which ironically isexposed by soil erosion, reports anincrease in fire related soil erosionduring warmer climate periods.Although such a large scale burn inYellowstone is unprecedented in ourmemory, the last one occurring in the1700s, Yellowstone has burnedbefore, and it will burn again. Wespoke with Professor Grant Myerabout fire-related soil erosion inYellowstone.

ER: Professor Meyer, what is yourtraining?

GM: I received a bachelor’s degreein geology in 1978 from the Univer-sity of Idaho and worked with theU.S. Geological Survey in the RockyMountain States. Then I went tograduate school in 1983 at MontanaState University and started doinggeological research in Yellowstonerelating to current volcanic andtectonic activity, unrest you mightcall it, in the Yellowstone caldera. Ifinished my Master’s in 1986 andworked for the Park Service inYellowstone for a few years. When Istarted my Ph.D. program in 1988, Idid not yet have a plan to work onthe Yellowstone fires, but it wascertainly a once in a lifetime oppor-tunity to look at the effects of largeand intense fires on the physicallandscape. When the debris flows

and floods started happen-ing in 1989, that prettymuch decided it for me. Ihad to work on that.

The work that isreported on in the Science

news article is part of my Ph.D.research, which I finished in 1993.Since that time I’ve been continuingwith related research, teaching atMiddlebury College, and recentlyaccepted a job at the University ofOregon Department of Geography.

ER: How did you get started on thisline of work?

GM: I got started with my researchthat involves the long-term activityof debris flows and sedimentation

park with prescribed fire, first, itwould be inordinately expensive andsecond, I don’t think it would work. Ithink it’s arrogant to think that weknow the biology well enough and weknow the geology and the fire historywell enough to be able to mimicnatural conditions.

I think the fires were a naturaloccurrence. The system basicallyreset its clock, and burned out standsof older trees are now undergoingsuccession with the younger trees.The fires did increase the amount ofthe edge between one patch andanother in the park. A number ofanimals take advantage of edges, sothat’s going to be good for them.

The fires allowed for a flush ofnutrients to go through to the aquaticsystems and fertilize them. Thegrasslands have pretty much goneback to a pre-fire status. We’re goingto see the effects of the fires in theforested part of the park fora long time.

ER: How do you feel aboutthe controversy about thefires?

LW: The fires were a remarkablething, and rather than being upsetabout it, I feel privileged to be able tohave seen it. Such fires have hap-pened many times before but we’venever witnessed it.

Literature Cited:Bill Wattenburg's letter to Sciencewas in the November 6, 1998 issue onpage 1051.

We now understand that fire is an integralWe now understand that fire is an integralWe now understand that fire is an integralWe now understand that fire is an integralWe now understand that fire is an integralpart of many forest landscapes.part of many forest landscapes.part of many forest landscapes.part of many forest landscapes.part of many forest landscapes.


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related to forest fires in late June of1988. The alluvial fans are depositsof sediment, generally coarse andgravelly, that exist along the base ofthe steep slopes of glacial troughvalleys such as Soda Butte Creek andSough Creek. They are basicallystorage locations or repositories forslope-derived sediment, which isthen gradually worked downstreamover the long term. In the northeast-ern part of the park, there was a largethunderstorm that caused erosion ofstream channels on the alluvial fansup in that area.

With that gullying of the alluvialfan channels, we can get a look atwhat’s inside of them. And we saw,even before the fires had started in1988, that many of the deposits inthose alluvial fans were rich incharcoal, suggesting that they wererelated to forest fires.

The 1988 fires and the eventsafter that — debris flows and floodscaused by thunderstorms on theburned slopes — provided a modernanalog so that we could then moreconfidently identify a fire-relateddebris flow inolder deposits.That is, we nowknow what fire-related sedi-ments look likefrom looking atthe modern examples.

ER: Were the fires the catastrophecritics claim?

GM: I think we’re at least somewhatbeyond the Smoky Bear stage whereforest fire was simply evil. We nowunderstand that fire is an integralpart of many forest landscapes. Butmany people are less likely to accept

fires that are what you might callcatastrophic, that burn intensely overlarge areas. And two, it is hard toaccept that there would be seriousslope erosion and sedimentationrelated to those fires.

Even with many fire ecologists,there is an assumptionthat if a fire has burnedhot enough and exten-sively enough that itresults in serious slopeerosion and debris flows,then there must besomething unnaturalabout that fire. It isassumed that fire manage-ment or other changesthat humans have made inthe landscape are whatcaused the fire to becatastrophic. There is also theassumption that nature doesn’t causemassive erosion or debris flows, thatmust be humans’ fault.

So testing whether debris flowswere associated with fires in the past,or whether the post-1988 debrisflows are a result of some change

that humans have made in thelandscape was the major goal of mywork. And clearly that researchshows that debris flows related tofire were common in the past.

ER: Common meaning every fewhundred years?

GM: Yes. The data on fire-relatedsedimentation events are consistent

with the estimates that were made bypeople like Bill Romme using treering data prior to 1988, that majorfires had recurrence intervals of 300to over 400 years.

On the other hand, I think it’simportant to recognize that when we

look at the pattern offire-related debrisflows in the past, theydon’t occur on aconsistent 300 to 400-year cycle. There areperiods of time ofseveral hundred yearsin which there are fewfire-related debrisflows, and there areother periods of timein which you see manyfire-related debris

flows concentrated within a span of afew hundred years. Those kinds ofchanges track fairly well what weknow about climate changes over thesame period.

The clearest examples are inwhat are known as the Little Ice Ageand Medieval Warm Period. Exactly

when the Little IceAge occurreddepended on whereyou were in theworld, but there’sclear evidence thatin North America

there was marked cooling about1300 A.D. That’s also the time whenI see fire-related debris flows andsedimentation drop off to minimallevels. It doesn’t pick up again untilthe 1700s — which is when the lastsignificant fires occurred inYellowstone — but still, fire-relatedsedimentation was relatively minor.However, if you consider 1988 to bepart of the record, then we appear to

...debris flows related to fire were common in the past... and...debris flows related to fire were common in the past... and...debris flows related to fire were common in the past... and...debris flows related to fire were common in the past... and...debris flows related to fire were common in the past... andmajor fires had recurrence intervals of 300 to 400 years.major fires had recurrence intervals of 300 to 400 years.major fires had recurrence intervals of 300 to 400 years.major fires had recurrence intervals of 300 to 400 years.major fires had recurrence intervals of 300 to 400 years.


8


be moving toward a period wheremajor fires may be more common.This is consistent with the generalwarming of climate in the last onehundred years.

Prior to the Little Ice Age,before 1300 A.D. and in particularfrom about 1050 A.D. to 1200 A.D.,was the Medieval Warm Period.More broadly it would be from about900 A.D. to 1300 A.D. Again, whatwas going on and when it happeneddepended on where exactly you werein the world. There are a number ofclimate proxy records from aroundthe world that suggest a warmerclimate during that time. That’s notto say it was uniformly warm, but,for example, there were severedroughts in what is now California,especially around 1150 A.D. Thiswas the same generaltime when the Vikingscolonized Greenland;they also disappearedfrom Greenland when itgot colder around 1300A.D. During the Medi-eval Warm Period is thelast time there was a bigpulse of fire-related debris flowactivity in Yellowstone especially,right around 1150 A.D.

It’s pretty clear that the largefires that precede the debris flowscorrelate strongly with the generalclimate. It’s not to say that it needsto be uniformly warm and dry duringa long period for a big fire to occur,but when the climate is warmer thenit’s more likely that you’re going toget the kind of severe drought thatoccurred in 1988.

ER: Do you think fire managementcontributed to the severity of thefires?

GM: I would say that the meteoro-logic factors of 1988 were by far themost important thing. It’s not to saythat fire management had no impact.

And from what I understand ofthe tree ring records, which give usgood detail for the last few hundredyears, there is no real evidence ofany change in the fire regime from,say, frequent fires that clear out theunderstory to less frequent fires afterfire suppression in the subalpinelodgepole-dominated forests thatcover the great majority ofYellowstone.

On the other hand, there aresome places at lower elevations, theDouglas fir and sagebrush grasslandareas of the northern winter range,that the fire frequency did decline atabout the same time the park was

established and people startedfighting fires. But that’s the lowest,most accessible part of the park. It’shad a road through it since thebeginning of the park to access theCooke City mining area. It’s easy totravel in, so fires there are mucheasier to control. But that’s a rela-tively small part of the park and it’snot the area which experienced thewidespread canopy burns in 1988.

ER: Fire management wasn’t thateffective in the area that burned.

GM: That’s right. In the subalpinelodgepole forests prior to the use ofaircraft in firefighting — basicallyprior to World War II — it mighttake you three days to get down inthe southeast corner of the park tofight a fire. And by then if that firewas going to go anywhere it wouldbe beyond the size you could controlanyway.

Some of the 1988 fires startedand reached uncontrollable sizewithin a few hours. The 1988 fires ingeneral were well beyond thecapability of current techniques todeal with, much less back in horse-back days. Sometime in the 1940sfire suppression could become moreeffective, but then it’s only a fewdecades until 1972 when the naturalfire policy was instituted. So in terms

of a period for fire sup-pression to be effective inthe lodgepole forests, itdoesn’t amount to much.

There’s also nothingabout what we know aboutthe lodgepole forests ofYellowstone prior to anyEuropean impact that

suggests that they tended to burnwith frequent low-intensity fires theway the Ponderosa pine forest did inwarmer, drier environments in theWest. The trees in Yellowstone growclose together and they havebranches extending close to theground. When the first Europeanexplorers visited the park, theydescribed a great deal of dead wood,both from past fires and deadfall,that is fuel for large fires. So theforest hasn’t significantly changed inbasic structure due to anything thatwe’ve done over that time. Andlodgepole pine trees are adapted to

During the Medieval Warm Period is the lasttime there was a big pulse of fire-related

debris flows in Yellowstone especially, rightaround 1150 A.D.


9


... it doesn't take that long after the fire for soilsto stablilize. That's in contrast to a logged basinwhere more than anything it's the road systemthat will continue to generate excess sediment

over long periods of time.

regenerate after fire, as they’ve donequite dramatically since 1988.

ER: What were people most con-cerned about as the damage of thebig fires?

GM: I think that probably mostfundamentally the fires were adramatic, visible change to thelandscape. Even people who hadbeen in the park for a long timelamented the fact that the park wouldnever look the same again. Theplaces that they knew well will nolonger be forested, at least by maturetrees. There were also completelynonscientific claims that the soilwould be sterilized, preventingregeneration. This has been demon-strated not to be the case. Soil is anextremely good insulator, and theonly way that you’regoing to heat the soil tothe point of killingseeds and rhizomescompletely within it isif you’ve got a bigdowned log that’ssitting just above thesoil surface and itburns a long time, andthat’s a localizedeffect. Even in areaswhere the fires burned the hottest,the lodgepoles are popping up.

ER: What about the fire-caused soilerosion?

GM: With sedimentation after thefires, clearly there are negativeimpacts. For example, debris flowscarry everything from boulders tomud to logs down into streams. Insome cases the flow itself can

completely wipe out a fish populationin that particular stream, althoughwithin the park itself I’m not awareof any such cases that have beendocumented.

The impact is in part a functionof the landscape in Yellowstone.Typically in the northeastern part ofthe park, and in the Absaroka Rangein general, where many debris flowswere occurring, relatively small,steep tributaries draining the valleysides experienced debris flows. Ifthere were any fish in these tributar-ies they were wiped out, but most ofthese streams have small, if any, fishpopulations. Those debris flows didnot remain debris flows as they wentinto the main streams. They turnedthe stream muddy, but that mud andcharcoal that washed on down themain streams didn’t have the direct

effect of killing fish.If you look at the longer-term

effects, then you think about theeffects of the sediment on thestreams. We generally understandthat an excess of fine sediment is badfor both fish habitat and fish spawn-ing success because it clogs up thegravel. Animals that live in thespaces between the gravel are ex-cluded, and fish eggs within thegravel don’t get oxygen and so theydie.

On the other hand, the nature ofthe sediment delivery to streamsafter fires is transient. In otherwords, it doesn’t take that long for itto die out because the basins reveg-etate. It doesn’t require regrowth of aforest to cut down on the sediment.All it takes is a relatively sparsecover of herbaceous plants, which inmost places popped up even the firstyear after the fire. Of course, a lot ofthose are annuals, so you can still getsediment coming down from a heavystorm, say, in the spring before theplants are up. Of course, after a fewyears then you have the dead plantthatch covering the surface.

The main point is that, in general,it doesn’t take that long after the

fire for soils to stabilize. That’s inpretty direct contrast to a logged

basin, where more thananything it’s the roadsystem that will continueto generate sediment andcause excess sediment tobe delivered to streamsover long periods oftime. That doesn’t goaway for many decades.We’re still trying tounderstand how long itwould take for a land-

scape to stabilize that’s been heavilylogged and roaded.

ER: We’ve got that experimentgoing on here in the Northwest.

GM: Definitely. So looking at the1988 fires from an ecologicalstandpoint, you also have to considerthat if these debris flows were thatdevastating over the long term to fishpopulations, then why do we have


10


Warmer Nights andWarmer Nights andWarmer Nights andWarmer Nights andWarmer Nights andChanges in PlantChanges in PlantChanges in PlantChanges in PlantChanges in PlantCommunity StructureCommunity StructureCommunity StructureCommunity StructureCommunity Structure

Introduction:

Global minimum temperaturesare rising faster than the averagemaximums; that is, nights arewarming faster than the days. Theecological consequences of thistemperature shift to plant communi-ties are unknown. In his work on

grasslandplantcommuni-ties in thehigh plainsof Colo-rado,RichardAlwardfound thatthe domi-nant grassspecies,blue grama,

grows less when nighttime tempera-tures increase1. The potential conse-quences of decreased growth by thedominant plant could be increasedsusceptability to invasion by exoticspecies, and/or decreased toleranceto drought and grazing. We spokewith Richard about his work and itsrelation to global warming.

ER: Richard, what is your positionin the academic food chain?

RA: I’m a graduate student atColorado State University, but I’mdefending my Ph.D. dissertation thismonth and I’m looking forward toshifting trophic levels. I am a grass-

any fish? Because it’s pretty clearthat major fires and debris flowshave been going on in Yellowstoneever since the last glaciation.

There are also positive aspects tofires and debris flows for aquatichabitats. They add woody debris tostreams, big logs which help main-tain structure within the stream suchas pools and riffles. Probably moreimportantly, in Yellowstone they putboulders in streams, which does thesame thing, they add more pool anddrop structure to the channel ratherthan a fast, shallow riffle. They addsediment of all sizes. And especiallyin many the larger streams, thepebble and cobble gravel that makesfor good spawning habitat for troutcan get flushed out if it’s not replen-ished. Especially for a powerfulstream like the lower Lamar River orthe Yellowstone River itself, thatkind of gravel tends to disappeardownstream unless it’s being addedto, so it can help to maintain spawn-ing habitat as well.

Probably the most importantthing is that fires are not going to bea problem as long as the ecosystemis not so fragmented that we’reputting all our eggs in one basket. Ifyou restrict your wild areas to thoselittle vest pocket watersheds here andthere, it’s easy for a catastrophicevent like a debris flow or a land-slide to have a devastating impact onthat small area. But with a largerintact area then those kind of distur-bances are quickly patched byrecolonization from other areas, andin the long run, the disturbances areintegral processes that maintainecosystem functions.

ER: There’s a debate in the ecologi-cal community about how big is big

enough to protect things. Do youthink the greater Yellowstoneecosystem, including the park, islarge enough?

GM: That’s a tough question, but Iwould say no, it’s not big enough.Perhaps early on it was, in the earlypart of this century and before. Notthat there weren’t major impacts ofother kinds in that period, but stillthere were large areas in the greaterYellowstone region that were leftpretty much alone, even though theyhad no legal protection. But we’reclosing up thefence aroundYellowstonein manyways: a greatdeal moredevelopmentof all sorts,recreationaland residen-tial included.We’recountingmore andmore on Yellowstone to function asan island. And then we have theseunforeseen things occur like laketrout being illegally introduced intoYellowstone Lake. Exotic speciesare probably one of the biggestproblems in the park and we haven’teven talked about that.

Additional Reading:

Meyer GA, Wells SG, Balling RC Jr,Jull AJT 1992 Response of alluvialsystems to fire and climate change inYellowstone National Park: Nature357: 147-150

Richard Alward collecting vegetation data atRichard Alward collecting vegetation data atRichard Alward collecting vegetation data atRichard Alward collecting vegetation data atRichard Alward collecting vegetation data atone of the warmed plots at his study site.one of the warmed plots at his study site.one of the warmed plots at his study site.one of the warmed plots at his study site.one of the warmed plots at his study site.


11


land ecologist, so studying at CSUhas been good for getting an ecosys-tem perspective; furthermore, CSU isinternationally recognized for itsstrengths in grassland ecosystemecology. I completed a M.S. degree at theUniversity of Nebraska where Ireceived a more population-orientedfocus on grassland ecology. I’m backat Nebraska starting on a post-docposition and I’mexcited about askingquestions and doingresearch that is notrestricted to just onelevel of ecologicalorganization. Iwould like to domore work address-ing multi-levelquestions within thesame researchproject.

ER: What would bean example of that?

RA: Well, I partici-pated in a workshopin February in whicha good number of ecologists fromaround the world were working to tryto synthesize data from a largenumber of studies on ecosystemresponses to global warming. Mostof the discussions were aboutecosystem-level questions, forexample, about flows of energy andmatter, sizes of carbon pools, andrates of carbon flows, and nutrientlimits on flows. On the other hand,we recognized that we did not havemuch data on what was happeningoutside of the dominant plant spe-cies, or to changes in abundance inindividual species, not to mention

how warming affects competitiveinteractions or the interactionsbetween plants and their herbivores. Those latter are more populationand community sorts of questions.And so I’d be interested in setting upexperiments in which we would, forexample, measure the nitrogenactivity in the soil and changes inhow plants are storing or respiringcarbon, in addition to looking at

what’s going on with biodiversity, orparticular species, and trophicinteractions.

ER: Integrating ecosystems andpopulation biology?

RA: Right. I think there’s too muchof a dichotomy between the two. Weget trained to do one thing or theother.

ER: How did you get the idea towork on this problem?

RA: Originally my wife, whocompleted her PhD at CSU, pointed

out that average temperatures hadbeen warming at the Central PlainsExperimental Range (CPER) inColorado. And knowing there werealso some long-term data sets onvegetation, I put a rough analysistogether and turned this in for a classassignment. I then decided it mightmake a good introduction to mydissertation, explaining why I wasdoing the experiments and why I

think they are important, so Iput much more effort intorefining the analyses andidentifying trends. I think thefinal product is a real goodexample of what ecologistscan gain from taking advan-tage of the long-term datasets that are available atthese long-term ecologicalresearch (LTER) sites.

ER: Where is your researchsite?

RA: The CPER site is 60kilometers northeast of FortCollins, Colorado, and it’spart of the Shortgrass Steppe

LTER. The site is largely level, itdoes have some minor topographicrelief, some little slopes and depres-sions and hills here and there, butyou can see to infinity if you lookeast and you can see to the RockyMountains if you look west. The vegetation is mostly short,predominantly grasses. In additionthere are many species of forbs (wildflowers) and some dwarf shrubs,many of which are not much morethan a foot tall. Shrubs increase inheight and dominance in areas wheresoil water and soil texture aredifferent than in the areas thatsupport grasses. There are a number

The view west from the study site across the short grassThe view west from the study site across the short grassThe view west from the study site across the short grassThe view west from the study site across the short grassThe view west from the study site across the short grasssteppe to the Rocky Mountains.steppe to the Rocky Mountains.steppe to the Rocky Mountains.steppe to the Rocky Mountains.steppe to the Rocky Mountains.


12


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of stream beds that cut through thearea, few of them ever carry flowingwater except in very rainy years.This is a semi-arid ecosystem withinthe rain shadow of the Rocky Moun-tains.

ER: Is it more or less pristine?

RA: Well, yes and no, it dependswhat you call pristine, so let meexplain my answer. If you were tojust drive by, you’d see lots of grassand pronghorns, and in a wet year,you’d see lots of wildflowers in thespring. So, you could reasonablyconclude it was pristine (although ifyou were from Kansas, where youget two to three times as much rain,it might look pretty barren, evenovergrazed).

However, the reason the CPER ispublic land is because it was

once homesteaded land that wasabandoned and the governmentbought it back. It’s pretty tough tomake a living from dry land farmingin this region. Recently, researchersfrom CSU examined old aerialphotographs and identified manyareas that had been plowed fifty ormore years ago. It’s now verydifficult to distinguish some of thesepreviously plowed areas from virgingrassland.

On the other hand, someareas had been planted with exoticgrasses, and these are obviouslydifferent from native grassland eventoday. The primary use of this landnow is for cattle grazing, and this iscertainly a low impact use whencompared to something like row-cropping.

ER: What’s the situation withexotics there now?

RA: As I just mentioned, there arethose areas that have clearly beenplanted to other species. I don’tknow whether those planted exoticsare declining as the natives disperseinto those areas. But the nativegrassland species, especially thedominant species, are pretty adept atholding on tight; under normalconditions it’s hard for any otherplant to invade. Empty space forexotics to gain a foothold is actuallypretty scarce. To a casual observer,there might look to be a lot ofopportunity for invasive plants sincethere is a considerable amount ofspace between plants aboveground.However, in this ecosystem, most ofthe plant mass is in the roots, andthere is actually very little emptyspace below ground.

The exotics are here but in mostcases they are confined to

heavily disturbed areas, like alongthe edges of roads. They play a smallpart in the system right now, but theyare within fighting distance, waitingfor us or mother nature to open up anopportunity for them. If we greatlydisturbed an area, I would expect tosee them expanding from the roadcut disturbances and moving intothese new disturbed areas. Also, oneyear recently when the CPER had anexceptionally wet spring, we sawexotics in areas they had not beenseen before.

ER: Is this a fire-driven prairie likethe tall grass prairie back east?

RA: I’m certain fire plays some rolebut not the major role that it wouldfarther east. Part of that is there’s alot more spaces between the above-ground vegetation, and there isn’t

that much mass to burn, so firesdon’t move very far. You get alightning strike and it burns, butgenerally it burns out before you getthe big wildfires, especially if thearea is grazed. So it’s got to playsome sort of role, but more of asmall-scale disturbance than any-thing major.

ER: What about the global scalewarming versus your site?

RA: First, I’d like to be clear that wehaven’t done any analyses at theglobal level, but our studies at thissite were inspired by recent analysesof historical climate records done atthe global level2. These researchersreported that global minimumtemperatures have been increasingtwice as fast as the maximumtemperatures. Minimum tempera-tures are the nighttime lows, whereas


13


maximum temperatures are thedaytime highs. So, nights have beengetting warmer, not the days. We analyzed the historicalclimate data for our site to identifywhat, if any, warming trends weretaking place. There has been a recentperiod of warming, so we then askedthe question of what was driving theincrease in the average: was it thenight or the day temperatures? Wefound that the nighttime lows havebeen increasing pretty dramatically,whereas the daytime highs haven’tchanged much at all.

ER: How far back did you look?

RA: We went back to 1964 becausewe specifically wanted two things:one, we wanted to takea period in which wecould see averagetemperatures wereincreasing so that wecould address thequestion of whether itwas change in night orday temperatures thatdrove the warming atour site. We’re notimplying that our sitedata can be scaled up tosay we have evidenceof global change. Butwe are saying that wesee the same tempera-ture patterns at our siteas others have found atthe global level over the last fiftyyears or so.

There’s another a priori reasonto restrict our analysis to this recentperiod. Our main question waswhether vegetation in the shortgrasssteppe is sensitive to changing night

temperatures. The CPER has goodvegetation monitoring data, using astandardized method only since the1970s. So even if we had used earliertemperature data, we don’t have thevegetation data to compare to it.

So right away I was pretty excitedabout this study. Night tempera-

tures at the CPER were doing thesame thing that others had detectedat other spatial and temporal scales.And, I had access to good vegetationdata. In all honesty, it didn’t seemlikely that I would find any interest-ing correlations between nighttemperatures and vegetation. For onething, it’s been repeatedly shown thatshortgrass steppe vegetation is veryresponsive to changes in precipita-

tion – nobody had ever suggested tome that temperature could be morethan just a minor factor. Also, I hadthe same preconceived notions thatmost of us have when we think aboutconsequences of climate change. Ithought about the effects of the days

getting warmer, and thus assumedthat climate change would lead toless pleasant conditions, in thesummer at least, and maybe morepleasant conditions in the winter.

We began looking for correla-tions between vegetation data andtemperature data. For the tempera-ture data, we included maximum,minimum, and average temperaturesfor each year and for the seasons(winter, spring, summer, fall) foreach year. We also included annualand seasonal precipitation in theanalyses. For the vegetation, weincluded data at the species level andat various groupings of species(functional groups) for net primaryproduction, which is basically the

harvested mass at the endof the growing season;and for abundance, thenumbers of plants grow-ing in an area.

ER: You’re trying todifferentiate between anoverall averagetemparature rise, and avegetation change thatcorrelates only to thenighttime increase?

RA: Right. We tookthese multiple data setsand did some prettysimple statistical analy-ses, and we found some

very striking correlations. The moststriking one was that the dominantgrass, which is blue grama(Bouteloua gracilis) declined inproduction as spring minimumtemperatures increased. That’s apretty important result because thisgrass is a major dominant. In our

Blue grama is more than 90 percent of the plant cover in theBlue grama is more than 90 percent of the plant cover in theBlue grama is more than 90 percent of the plant cover in theBlue grama is more than 90 percent of the plant cover in theBlue grama is more than 90 percent of the plant cover in theshort grass steppe.short grass steppe.short grass steppe.short grass steppe.short grass steppe.


14


region of the shortgrass steppe, andin many others, it can be up to 90percent of the plant cover.

ER: That’s dominant.

RA: Yep. That’s in the area itcovers. Another way to look at it ison a mass basis, in which case, it’sabout two-thirds of the plant massout there.

ER: So as the temperature goes up,the grass’s productivity goes down.Does productivity go up when thenighttime temperature goes down?

RA: I don’t know, we don’t have acooling trend in our data sets to lookat the question this way. Of, course,if we’re lucky, andclimate doesn’t warmup, we might have achance to look at this.To summarize ourcurrent thinking aboutthis, we’ve got evi-dence that production by somespecies in this ecosystem is corre-lated with the minimum temperature.This is now our hypothesis tomotivate our experimental efforts tofind out if indeed temperature isdriving these trends or if there couldbe something else going on.

ER: Different rainfall pattern orsomething like that?

RA: Right. But we tried our best toget other climate factors to correlatewith productivity. We looked atannual and seasonal precipitation.We tried to look at all the differentprecipitation parameters. We lookedat average temperatures and we

looked at maximum temperatures.Annual precipitation was moststrongly correlated with total ecosys-tem production, but this is somethingthat others have found repeatedly.

What was surprising was thatthis minimum temperature

variable kept popping up with thestrongest correlations for importantspecies and plant functional groups.So we’re pretty confident that we’regoing to find that minimum tempera-tures is indeed what’s causing thischange in productivity. But based onthis one paper, we cannot say that itis certainly causing it.

ER: Were other plants changing outthere?

RA: The exotic forbs correlation isbased on pretty small numbers. Wecouldn’t see any patterns in any ofthe particular species of exotics. Theonly time we detected a pattern is ifwe lumped them all together. Ofcourse, the site where the plant datais collected may bias against findingmany exotics; it’s out in the middleof a pasture away from the roads.I’m sure the site was selected in partto avoid the sorts of edge effects thatmight be picked up if it was closer toa road. There aren’t that many exoticsout in the middle of the pastures

right now, and thus the numbersavailable for analysis was small.Despite these caveats, the numbersshow a significant increase, and it’sworth being concerned about it.These exotic forbs share similarfeatures with all the other plants thatwe found were increasing; a featurethat is strikingly different from thedominant grass.

ER: Do you have a scenario for howthe community might change?

RA: One way of separating plantsinto two functional groups is basedon the two different photosyntheticpathways these plants use. One iscalled the C

4 plants, which are

commonly called warm seasonplants. These are plantsthat grow best in the hotsummer, and this groupincludes blue grama.The other is called theC

3 plants, which are

commonly referred toas cool season plants. These are theplants that get growing best early inthe spring (like Kentucky bluegrassof many lawns), and by the time itgets hot in July and August they’vepretty much flowered and are donegrowing.

We’re seeing an increase inplants associated with cool seasongrowth and a decrease in plantsassociated with the warm seasongrowth. And with some strikingexceptions, most of our problemplants, our weeds, are cool seasonplants. They get started early in thegrowing season, they use up soilresources, whether water (the mostimportant thing in semi-arid sys-

... the nighttime lows have been increasing pretty... the nighttime lows have been increasing pretty... the nighttime lows have been increasing pretty... the nighttime lows have been increasing pretty... the nighttime lows have been increasing prettydramatically, whereas the daytime highs haven'tdramatically, whereas the daytime highs haven'tdramatically, whereas the daytime highs haven'tdramatically, whereas the daytime highs haven'tdramatically, whereas the daytime highs haven'tchanged much at all.changed much at all.changed much at all.changed much at all.changed much at all.


15


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Mismanagement of Fisheries:Mismanagement of Fisheries:Mismanagement of Fisheries:Mismanagement of Fisheries:Mismanagement of Fisheries: LouisBotsfordRestoration of Mono Lake:Restoration of Mono Lake:Restoration of Mono Lake:Restoration of Mono Lake:Restoration of Mono Lake: RichardRidenhourThe Forgotten Pollinators: The Forgotten Pollinators: The Forgotten Pollinators: The Forgotten Pollinators: The Forgotten Pollinators: StephenBuchmann

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What You Need to Know About Creation-What You Need to Know About Creation-What You Need to Know About Creation-What You Need to Know About Creation-What You Need to Know About Creation-ism:ism:ism:ism:ism: Robert PennockBrown Tree Snakes Cause an EcologicalBrown Tree Snakes Cause an EcologicalBrown Tree Snakes Cause an EcologicalBrown Tree Snakes Cause an EcologicalBrown Tree Snakes Cause an EcologicalDisaster in Guam:Disaster in Guam:Disaster in Guam:Disaster in Guam:Disaster in Guam: Thomas Fritts

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Coral Reefs: The Rainforests of theCoral Reefs: The Rainforests of theCoral Reefs: The Rainforests of theCoral Reefs: The Rainforests of theCoral Reefs: The Rainforests of theOceans:Oceans:Oceans:Oceans:Oceans: Don HinrichsenRed Cockaded Woodpeckers:Red Cockaded Woodpeckers:Red Cockaded Woodpeckers:Red Cockaded Woodpeckers:Red Cockaded Woodpeckers: ProtectedYet Declining: Jerome Jackson

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Tracking Radioactive Waste in theTracking Radioactive Waste in theTracking Radioactive Waste in theTracking Radioactive Waste in theTracking Radioactive Waste in theFormer Soviet Union:Former Soviet Union:Former Soviet Union:Former Soviet Union:Former Soviet Union: Don Bradley andMichael FoleyExotic Species and Restoration ofExotic Species and Restoration ofExotic Species and Restoration ofExotic Species and Restoration ofExotic Species and Restoration ofDegraded Ecosystems: Degraded Ecosystems: Degraded Ecosystems: Degraded Ecosystems: Degraded Ecosystems: Wayne Richter

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Rivers As Sentinels: Why We Are LosingRivers As Sentinels: Why We Are LosingRivers As Sentinels: Why We Are LosingRivers As Sentinels: Why We Are LosingRivers As Sentinels: Why We Are LosingWild Salmon in the West and What WeWild Salmon in the West and What WeWild Salmon in the West and What WeWild Salmon in the West and What WeWild Salmon in the West and What WeCan Do to Restore Them: Can Do to Restore Them: Can Do to Restore Them: Can Do to Restore Them: Can Do to Restore Them: James Karr

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Health Effects of Mercury in theHealth Effects of Mercury in theHealth Effects of Mercury in theHealth Effects of Mercury in theHealth Effects of Mercury in theEnvironment:Environment:Environment:Environment:Environment: Rita SchoenyIs American Agriculture Sustainable?Is American Agriculture Sustainable?Is American Agriculture Sustainable?Is American Agriculture Sustainable?Is American Agriculture Sustainable?Paul FaethWhat We Know About Climate Change:What We Know About Climate Change:What We Know About Climate Change:What We Know About Climate Change:What We Know About Climate Change:Jerry Mahlman

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Marine Conservation Biology:Marine Conservation Biology:Marine Conservation Biology:Marine Conservation Biology:Marine Conservation Biology: Elliot NorseUrban Population Growth in DevelopingUrban Population Growth in DevelopingUrban Population Growth in DevelopingUrban Population Growth in DevelopingUrban Population Growth in DevelopingCountries:Countries:Countries:Countries:Countries: Martin Brockerhoff

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A Judge Orders Wolves Removed fromA Judge Orders Wolves Removed fromA Judge Orders Wolves Removed fromA Judge Orders Wolves Removed fromA Judge Orders Wolves Removed fromYellowstone: Yellowstone: Yellowstone: Yellowstone: Yellowstone: Robert Pletscher and RobertKeiterSustainable Development in the Tropics:Sustainable Development in the Tropics:Sustainable Development in the Tropics:Sustainable Development in the Tropics:Sustainable Development in the Tropics:Richard Rice

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Sea Otters as Keystone Predators:Sea Otters as Keystone Predators:Sea Otters as Keystone Predators:Sea Otters as Keystone Predators:Sea Otters as Keystone Predators: JamesEstesTree Species Diversity in CommerciallyTree Species Diversity in CommerciallyTree Species Diversity in CommerciallyTree Species Diversity in CommerciallyTree Species Diversity in CommerciallyLogged Tropical Forests:Logged Tropical Forests:Logged Tropical Forests:Logged Tropical Forests:Logged Tropical Forests: Charles Cannon


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tems) or nitrogen, and sometimesgrow big enough to create shadows.Then when the native warm seasonplants start to get going, there’s lesswater and nutrients available, andthere may be shade on them.

Despite what we’ve foundfrom this study, I’d like to emphasizethat blue grama is a pretty incrediblelittle plant. It’s going to take a lot toknock it out of the system. However,a major concern is that if this speciesis reduced, the ability of the short-grass ecosystem to tolerate droughtand grazing may be reduced.

I mentioned that this paperreports “just” correlations, and theexperiments need to be done toidentify a cause and effect relation-ship. So here’s a little teaser: we’vebeen doing experiments out in theshortgrass steppe with warming upthe night temperatures during thegrowing season. And our preliminaryresults are showing the same patternsthat our Science paper described.We’re seeing the same patterns ofdecreases in the warm season plantsand increases in the cool season

plants. After two years the changesare small, but it’s a slow-changingsystem, so we’re not surprised thatwe’re just seeing small changes.

Literature Cited:

1 Alward, R.D., J.K. Detling, andD.G. Milchunas. 1999. Grasslandvegetation changes and nocturnalglobal warming. Science 283:229-231.2 Easterling et al. 1997. Science277:364

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