w11

)omething like the seven biblical plagues hasbeen visited upon the Coweeta HydrologicLaboratory study area in western North Carolina.

In recent decades drought, insect outbreaks,plant disease and even a hurricane have afflicted;the Coweeta watershed just three miles north ofthe Georgia border. But UGA and otherresearchers have discovered that these relativelyrare, seemingly damaging events actually replenishthe ecosystem with important nutrients. f

lake, for example, the fall cankerworm ouf- •break of the early 1970s. f I

"It's called the fall cankerworm because th| fadults fly in the fall, but the larvae attack in eajly 1spring," said D.A. Crossley, a UGA professor || I;emeritus of ecology. Crossley has conducted ; j: C |researchtat Coweefci sirvce^ the late 1 60s. He^y

in the

B Y S T E V E N N. K O P P E S

P H O T O G R A P H S B Y J A M E S S l R A W S E R

Y

•i When it comes to understanding•i southern. Appalachian* &Eb.loe^ the]. forest flporjs wherfe the "action is.1 'interceptecTjeaf litter, collected -byiTLe.es-McRae> Chandra H u s e n m . b e weighed

'5 to help mea'silUlutrieptJI through a CoweetS'tei^st.

$?v

The southern

Uppalachians are

a hotspot for

IA graduate

lansen has found

more than 160

soil mite species

in a research plot

measuring

approximately

20 by 40 yards.

"The increased amount of nutrients that arereleased are mobilized again and spark thatgrowth. This puts insects in a whole differentlight. Do you really want to control insects if theyare actually going to produce increased growth inthe forest?" Crossley asked.

Such questions about the response of forestand stream to natural and human-induced ecologi-cal disturbances can only be answered followingyears, even decades, of research. And that is thepurpose of Coweeta's Long-Term EcologicalResearch (LTER) Program, a cooperative effortbetween UGA and the USDA Forest Service.The Forest Service, which manages Coweeta,began conducting a steady stream of researchthere in 1934.

Early on, the Forest Service documented theharmful effects of land-use practices such asmountain farming, grazing and unrestricted log-ging on water flow in the forest. When UGAjoined the effort in 1968 with support from theNational Science Foundation, a new tributary ofecosystem data joined the mainstream of researchat Coweeta. NSF's support has continued eversince, contributing to Coweeta's record as thelongest continuously monitored landscape inNorth America.

Nature's perfect laboratory"We're like an ecological observatory," said

David Coleman, a UGA research professor ofecology. "We look at changes in our ecosystemover decades of time."

Research at Coweeta today encompasses col-laborations among 55 graduate and undergraduatestudents and 29 senior researchers from UGA, theForest Service, Virginia Polytechnic Institute andState University, Duke University, University ofMinnesota, Mars Hill College, University ofWisconsin at Madison and Portland StateUniversity. Much of the work focuses on theCoweeta basin itself, but the regional study areaincludes parts of western North Carolina, north-ern Georgia, eastern Tennessee and southernVirginia.

The bowl-shaped Coweeta basin covers8.4 square miles of the Nantahala National Forest.The basin ranges in elevation from 2,250 feet atthe Forest Service headquarters to the 5,250-footpeak of Albert Mountain a few miles distant.Enough water flows through the basin to supply acity of 30,000 people. Coweeta's waters flow steady

and clear but will continue to do so, decades ofresearch indicate, only if the basin's ecology remainsin chemical balance.

Coweeta's geology and its rainfall, which variesfrom 71 to 94 inches annually across its elevations,make it a perfect natural laboratory for studying howthe forest uses water. Impervious bedrock underliesthe basin, so researchers could install weirs — waterflow measuring devices — to precisely record forestwater use. Would a pine forest use more water than ahardwood forest under similar circumstances? Anongoing study provides conclusive evidence that theanswer is yes.

But the area's extraordinary biodiversity makes itan equally ideal setting for undertaking broader eco-logical research projects.

"The southern Appalachians are what we call ahotspot for biodiversity," Coleman said. TheCoweeta basin especially abounds in soil mites,which feed on fungus, decaying leaf litter and nema-todes. UGA graduate student Randi Hansen has

I iriFrfflffre

found more than 160 soil mite species on a researchplot measuring approximately 20 by 40 yards.

"That's a higher number than has been recordedfrom most any tropical site," Coleman said. "Youalways hear of the high species richness in the trop-ics. It's gospel. But it's not that simple."

Coweeta's soil mite diversity astounds evenCrossley, who began studying mites five decades ago."As ecologists, we know that many species shouldn'tbe able to co-exist on the same resource," he said.

Before joining the UGA faculty in 1967,Crossley conducted ecological research in a radioac-tive drainage system at Oak Ridge NationalLaboratory in Tennessee. Radioactive materials hadbeen released into the environment at Oak Ridge."We had wondered, how do you tell when an ecosys-tem is sick?" he said. "If it's running a fever, where doyou stick the thermometer?"

Then came a landmark paper published in thejournal Science by Yale University's Herb Bormannand Gene Likens. Bormann, formerly of Duke

University, had visited Coweeta many times. "Hetold me once that Coweeta was the inspiration forhis work on the watersheds up at Hubbard Brook inNew Hampshire, where he and Likens did theiroutstanding work," Crossley said.

Bormann and Likens snowed how elementssuch as calcium cycled within the watershed. Treestake up calcium and other elements from the forestfloor. The calcium returns to the forest floor afterthe leaves drop and decompose.

"About 95 percent of the calcium involved inthat cycle continued to cycle," Crossley said. "About5 percent was lost each year. This was made up byerosion from bedrock and by atmospheric deposi-tion. When the forest is disturbed — by cutting, byacid precipitation, something like that — thesecycles are altered."

The Coweeta LTER(Long-Term Ecological

Research) siteencompasses parts of

Georgia, North Carolina,South Carolina,Tennesseeand Virginia. Researchersfrom 21 academic disci-

plines have amassed shelvesof data (below) during

the six-decade study.

*mat.

Photo by Brian Kloeppel

The forest floorof the southernAppalachiansteems with anabundance of lifeforms, includingmillipedes (like theone above), sala-manders, shrewsand soil mites.(Illustration byScott Alexander)

How ecosystems workThe Bormann-Likens study showed that ele-

mental balance was the key to understandingwatershed ecology. The information came inhandy after Coweeta became part of theInternational Biological Program in 1968. TheNSF funded Coweeta as the program's easterndeciduous forest study site. Other sites included agrassland site in Colorado, a tundra site in Alaskaand an open forest site in Oregon. Nutrientdynamics meshed with hydrology in Coweeta'sresearch, with Forest Service and UGAresearchers working as full partners.

Initially, project scientists set out to measureecological productivity — the amount of energyavailable through photosynthesis — and its con-trolling factors in a variety of environments world-wide. But as the program developed, scientistsbegan to address a broader question: How doecosystems work?

"The project was importantfor us because we

learned a lot abouthow to do scien-

tific research inthat magni-tude,"

Crossley said."Most of us

were familiarwith one- or

two-year studies__ of perhaps two peo-

-*^:'.••_>..'-- pie. These were teams ofecologists, which was not an entirely new idea, butat this level it was certainly new."

Research teams were necessary because of thewide range of expertise needed to fully examinethe workings of an ecosystem. The specialties ofthe scientists who have overseen Coweeta'sresearch over the years hint at the project's inter-disciplinary scope.

First, during the International BiologicalProgram years, came botanist Carl Monk, nowretired. When the IBP gave way to the Long-Term Ecological Research Program in 1980,Crossley, a soil mite specialist, headed the UGAcontingent. Crossley handed the reins to streamecologist Judy Meyer in 1990, and she to DavidColeman, a microbial and soil ecologist, in 1996.

Wayne Swank, a hydrologist and ecologist,served as the Forest Service research leader from1966 to 1996. James Vose, who specializes in for-est ecology, succeeded Swank.

Together they and their colleagues monitorresearch sites throughout the Coweeta watershed.Some sites are devoted to streamside habitats,which ecologists refer to as riparian zones. Othersites focus on terrestrial processes that occur at

low, intermediate and high elevations, respectively.Some sites are left undisturbed, while others areexperimentally manipulated in some way.

Natural and man-made disturbancesMother Nature has created a few disturbances of

her own for researchers to monitor. And now, underthe pressure of recent population trends, socioeco-nomic questions have gushed onto Coweeta'sresearch agenda.

Experimental treatments have ranged fromclearcuts and prescribed burning to excluding leaf lit-ter or woody debris from stream beds with netting torecord their effect on nutrient flow.

Researchers initiated a commercial clearcutexperiment in a mixed hardwood section of Coweetaforest in 1976. Most trees on the watershed, includ-ing oaks, hickories, maples, black locusts and pines,were cut to see how their removal would affect forestfloor nutrient dynamics.

The idea was to remove the trees without dis-turbing the forest floor. The Forest Service madethis possible by developing a technique to raise andremove the logs by cable. "Normally, they'd be skid-ded across the forest floor," Crossley said. "It was ourthesis that leaving the forest floor intact wouldreduce the loss of nutrient capital from clearcutting."

Mother Nature complicated the experiment by

The Landscape

Remembers

wo types of halfbacks live in west-ern North Carolina. One carriesthe ball on the football field. Theother carries the fate of theregion's ecology.

"Halfback" is the nickname forpeople who first moved from the cold, industrialNortheast to south Florida. Now, for whateverreasons — the four seasons, the quality of life —they're coming halfway back, into the mountains

"North Carolina in the last 10 years has had anet immigration to the tune of 600,000 people,"said David Coleman, a UGA research professor ofecology. "That's like adding two entire congres-sional districts."

Working in the wake of this population influx,UGA researchers at the Coweeta HydrologicLaboratory came to realize that humans hadbecome the region's dominant ecological species.

R E S E A R C H R E P O R T E R

throwing in a couple of unexpected experimental para-meters. First came unusually heavy rains, followed byan unusually severe drought. But the researchers' thesisproved to be largely correct.

Today, the clearcut watershed sports a lush standof trees 30 to 40 feet tall and a diverse collection ofplants on the forest floor. In fact, the young forest har-bors more abundant species than do undisturbed areas.A book-length manuscript, now in preparation, will"describe these results.

Unfortunately, Coleman said, the clearcut experi-ment could not be repeated today. The Forest Servicehas banned clearcutting. Crossley disagrees with thepolicy.

"Small clearcuts, not massive ones, are probablythe best way to harvest forests in the southernAppalachians because there is such rapid regrowthfrom stump sprouts and root sprouts," he said. "Thepublic does not want it, however, so we don't do it."

^—-.^.saije .„••" '-" _,^y — ,. — -

% * P Ci fJ. fS^-MiS^^ i-l

The Coweeta Hydrologic Laboratory is the longest continuouslymonitored natural environment in North America. In 1934, the U.S.Department of Agriculture Forest Service began studying its steepslopes to learn more about wise management practices and to gain abetter understanding of forest ecology. Today's research team of 29senior researchers and 55 graduate and undergraduate students rep-resents the Forest Service, the University of Georgia and six othercolleges and universities.(Photo courtesy of Coweeta Hydrologic Laboratory)

A LEGACY OF D I S T U R B A N C E S

Now, ecologists work in collaboration with social scientists,analyzing human land-use patterns and attempting to predictbuilding density in the upper Little Tennessee River drainagefor the year 2030.

During the past 50 years, the trend appears to be towardallowing agricultural land to revert to its natural state. Butecological recovery rates between forest and streamside habi-tats differ dramatically.

"The forests pop back quickly. They maintain a lot ofthe biomass and productivity that we saw in previousforests," said Brian Kloeppel, Coweeta Long-TermEcological Research site manager. "But even 50 years after amajor disturbance, many of the streams still show a lot of thesame species and populations that they did in an agriculturalsetting. They normally have a lower diversity of species,more open areas, more erosion problems, that sort of thing."

The University of Minnesota's Paul Bolstad, a Coweetacollaborator who has studied the phenomenon, says it anoth-er way: "The landscape has a long memory."

— SNK

harvest trees, graze animals and til! the soil, allcausing heavy soil erosion, seasonal flooding andloss of forest habitat." ' ; / - ' : "'; -':-": The chestnut blight virtually elimi-nates the forest's dominant tree species.

Elm spanworm defoliates tree species acrossthe Coweeta basin."••• 7 Six autumn days of intense rain dump

worm cause tree defoliation and substantialincrease in stream nitrogen export." 7" "' r / Locust stem-borer outbreak defoliates23 acres of trees.

table and cause tree mortality on ridge sites."• r- " Hurricane Opal causes isolated flooding;high winds uproot many acres of trees.

defoliation.

A bigger ecological threat to Coweeta blowsm from metropolitan Atlanta. The Coweetawatershed sits within the atmospheric umbrellaof Atlanta, which produces a huge volume ofnitrogen oxides, sulfur oxides and other air pol-lutants. "We're like a big sponge sitting hereabsorbing these oxides," Coleman said.

Coweeta's older forests appear to haveentered the initial stages of nitrogen saturationdue to forest maturation and increasing input ofatmospheric nitrogen. Coweeta researchers won-dered what effect that would have in futuredecades on the vital microbial processes takbeplace on the forest floor.

"One of our LTER collaborators in southernMinnesota has found some net losses in biodi-versity when you heavily fertilize some grasslandplots, Coleman said. "We have to understandnatural purification processes and what wouldhappen if we get our system saturated."

Nitrogen comprises four-fifths of Earth'satmosphere. Like oxygen, which makes up mostot the other 20 percent of the atmosphere nitro-gen is essential to life on Earth. Nitrogen servesboth as food and fertilizer, but too much of theelement, especially in the form of nitrates, canslow plant growth and make drinking waterunsafe for humans.

"Stream nitrate concentration is a very sensi-tive indicator of forest ecosystem disturbance It'sthe bottom line," Swank said.

And Coweeta's pure waters make nitrateleakage easier to detect there than at other loca-tions, Crossley said.

"In the Northeast today, with as much nitro-gen deposition as they have had, they couldn'tsee it. It would not be above the backgroundlevel," he said.

Both natural and unnatural disturbances canresu t in stream water export of nitrates. An out-break of locust stem-borers killed a stand ofCoweeta's locust trees in 1979. The dead treesreleased a store of nitrogen from their roots,leaves and stems, increasing stream nitrate con-centration by 300 parts per billion. "Other vege-te^FP°f UP much ofAe nitrogen," Crossleysaid. Atthe'same time, much of it reached'the— and1 w&detecteddt iri tie stream water."

" "*•§ ajfo nieasured nitrate exportHurricane Opa

which blew through North Carolina, includingCoweeta, in October 1995. The hurricane hitexposed sites at high elevations, where the treeswere poorly anchored in relatively thin soils.

Opal even damaged one of the Coweeta studysites, throwing a stand of oak and poplar treesdownhill. The downed trees opened a researchopportunity along with a large hole for rainwaterin the forest canopy. The disturbance produced anitrate leakage of 50 to 100 parts per billion —about the same concentration that Swank hasmeasured following a forest harvest. Only 3 partsper billion were recorded before the hurricane.

Coweeta researchers are still recording a con-siderable concentration of nitrates draining intothe groundwater through this gap. "This is a fasci-nating thing for people who like to think aboutinfrequent events," Coleman said. "The lastrecorded hurricane damage in that part of westernMacon County in North Carolina was in the1830s."

Humans complicate the futureSome forest ecologists say that forests, when

left undisturbed, will reach an ecological equilibri-um after two or three centuries. But forest ecologyresearch at Coweeta tells a more complicatedstory.

"I'm well-aware, now, of the importance ofgap formation in the forest," Crossley said. Treesare struck by lightning, killed by insects orknocked down by hurricanes, opening gaps in theforest. The gaps allow new successions of plants toemerge. The relative abundance of specieschanges continually over the years for all kinds ofreasons.

Half a century ago, the American chestnuttrees dominated the region's forests. Then camethe chestnut blight, a pathogenic fungus importedfrom Japan, which all but wiped them out. But thenear extinction of the American chestnut hasallowed many other species to flourish instead.

"We lost the chestnuts to disease," Crossleysaid. "We call these natural forests, but the majortree species is gone. What's undisturbed about theundisturbed part of our controls? I think it's^safe

to say there aren't any natural areas left atCoweeta," he said. "There are only someless-disturbed areas."

Increasingly, humans causethese disturbances, Coleman said.

"With all these [people]coming into the area, and thatincludes me coming into this area14 years ago, we're going to haveto try to somehow lessen ourimpact," he said. The alternativeis to continue participating in ahuge, uncontrolled ecologicalexperiment. What would hap-pen if, say, the human speciesburned enough fossil fuels todramatically increase the carbondioxide composition of the atmos-phere?

Earth is a life-support system,not a marketplace. Organisms don'tget to choose what gases to breathe ifthe supply of their favorite ones comesup short.

"Folks, we're talking oxygen and carbondioxide. We've got some basic physiologicalprocesses going on here," Coleman said. "We'renot going to substitute for them."

For more information, e-mail David Coleman atcoleman@sparc.ecology.uga.edu or accesshttp://coweeta.ecology.uga.edu orhttp://www.lternet.edu/network/sites/index.html.

Steven N. Koppes, an award-winning writer, is the former UGAassistant director of research communications and associate edi-tor of Research Reporter. He has a bachelor's degree in anthro-pology and a master's in journalism and is a science writer at theUniversity of Chicago.

Markers like thesehelp researcherstrack the fate ofindividual plantsafter a natural orhuman-causeddisturbance.