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26 AUGUST 2005 VOL 309 SCIENCE www.sciencemag.org1314

Plant ecologist Christian Körner of the Uni-versity of Basel, Switzerland, goes to work bysoaring into the sky on a construction crane.He and his colleagues squeeze into a four-person cage and, in 30 seconds, are carried up 30 meters. The crane operator guides the gon-dola to the end of the 45-meter-long boom andslowly lowers it, leaving Körner and his col-leagues dangling just above the 30-meter-talltreetops of the Swiss forest they’re studying.

Körner’s first ride more than a decadeago was an eyeopener. “Thecanopy was not the green carpetwe thought, but highly structured,with peaks, gullies, canyons, and deep gorges among somecrowns,” he recalls.

Once a novelty, cranes havebecome essential for sorting outforest dynamics, say ecologists.Most of a tree’s photosynthesisoccurs in its canopy—the upperleaves, twigs, and branches—and40% of the world’s terrestrialspecies live there. From their loftyperches on cranes, researchers havebeen counting species and studyingleaf and tree physiology formore than a decade. More arenow turning their attention toglobal change. Körner, forexample, wants to know howforests capture greenhousegases. On page 1360, he andhis colleagues report findingsfrom the first phase of a long-term experiment looking atcarbon dioxide’s effects inestablished forests. “[Thisstudy] is our first real glimpseof how mature forests mightrespond to increasing concentration of atmos-pheric carbon dioxide,” says Kurt Pregitzer, anecologist at Michigan Technological Uni-versity in Houghton.

Körner is among several hundred ecolo-gists, plant physiologists, taxonomists, andconservationists who have moved their stud-ies off the forest floor to the more productive

upper layers. These researchers work atabout a dozen crane sites scattered aroundthe world (see map, p. 1315). But if they cancobble together a relatively modest amountof money, these researchers have even moreambitious plans. In an effort called theGlobal Canopy Program (GCP), Körner andhis colleagues are pushing to double thenumber of research cranes and train morestudents, scientists, community leaders, andeducators in their use.

From the top

Linking the earth and sky,canopies harvest energy

from the sun and create organic matter.They provide moist and dry spots, as well aswarm and cold pockets, making possible ahuge diversity of forest fauna. Canopiesalso play a role in global climate change,although researchers have yet to pin downexactly how. For example, trees suck in car-bon dioxide for use during photosynthesis,

whereas microbes release it by degradingfallen canopy leaves.

Although forest researchers are oftenwilling to don climbing equipment to scaletree trunks or build walkways that swayamong the branches, these strategies affordonly a partial view of the canopy. The tops oftrees either can’t be reached from below orcan’t support the weight of people. In con-trast, cranes offer a top-down perspectivethat forest researchers have wanted. In the

past 15 years, “cranes havebecome the symbol of canopyresearch,” says Kamal Bawa,head of the Ashoka Trust forResearch in Ecology and theEnvironment in Bangalore, India.

In 1992, Alan Smith of theSmithsonian Tropical ResearchInstitute (STRI) in Panama wasthe first to get this bird’s-eye viewof a canopy, using a 40-meter-high crane set up among the treesin a Panama City park. The vistawas breathtaking and the view ofthe greenery below, stupendous.By swinging the crane’s boomaround in a circle and shuttlingthe gondola along its length andlowering the cage to differentheights, researchers could finallyget the big picture of a canopy.

A second crane was set up in1997 in a different spot in Panama,a site where some 85 ecologists andtaxonomists are now using a rangeof techniques designed to pin downthe number and identities of arthro-

pod species in the canopy. Established in 2003,the arthropod project now has 400,000 speci-mens and 1080 species in its archives. As itcontinues, researchers expect to find manythousands more specimens and large numbersof new species. Only with this many samples“can the many patterns of diversity, commu-nity organization, and functional roles of indi-vidual taxa [in the canopy] be understood,”says forest ecologist Andreas Floren of theUniversity of Würzburg, Germany.

Using construction cranes to reach above towering treetops, scientists are achieving a better overview of forestecology and how trees contribute to global climate change

Sky-High Experiments

News Focus

Lift off. Körner (inset) and his team do theirwork dangling 30 meters above the ground.

Published by AAAS

Once Panama’s cranes began provingtheir worth—typically the investmentrequires several hundred thousand dollarsper site—other groups began procuringcranes for temperate sites. In 1999, Körnerused a helicopter to deposit a crane in a century-old Swiss woodland, whose treestower 30 or more meters above the ground.Despite the importance of biodiversity stud-ies, Körner took another tack with his crane.“A logical next step [was] getting involved inthe larger process studies,” including experi-ments related to greenhouse effects, he says.

Until Körner’s project, those studying theforest effects of increased carbon dioxidehad limited their attention to young trees—no taller than 16 meters and primarily in single-species plantations of sweet gum orloblolly pine. In these younger forests, ecolo-gists pumped carbon dioxide fromtowers to blanket the young trees.However, they could not applythis technique to taller, moremature trees.

Körner overcame this draw-back by placing 10 kilometers ofdrip irrigation tubing among theupper branches of a 500-square-meter plot. His team pumped car-bon dioxide through the tubing,delivering 50% more than ambi-ent concentrations to each tree.“My prime intention was to breakthe technological barrier that sofar limited research to young, vigorously growing trees,”Körner explains.

The carbon dioxide pumpedthrough the tubing incorporatedmore than the usual amount of anunusual carbon isotope, distin-guishing it from the gas absorbed normallyfrom the atmosphere. In this way, Rolf Sieg-wolf and Sonja Keel of the Paul ScherrerInstitute in Villigen, Switzerland, were ableto track the fate of the extra carbon as itcycled through the forest ecosystem. At thesame time, Körner’s graduate studentRoman Asshoff monitored tree growth.“This is certainly a much more realisticapproach than studying potted plants oryoung trees in plantations,” says Yves Basset, an STRI entomologist.

By focusing on mature trees and extend-ing measurements to the ground, Körner wasable to assess tree-soil interactions. Whereasyoung trees use extra carbon to speed upgrowth, mature ones don’t, he and his col-leagues report in this week’s issue of Science.Instead, much of this carbon winds up in theroots, ultimately moving into the soil, wheremicroscopic fungi take up much of it. Thanksto microbial activity, “this carbon is rapidlyrecycled to the atmosphere through the rootzone,” says Körner.

Different species of trees processed theextra carbon differently, but some trendswere clear. Overall, carbon in the soilincreased by 44%. Fur thermore, themakeup of decomposing leaves changed.Lignin, a polymer that combines with cellulose to stiffen trees, dropped by 11%, whereas the amount of starches andsugars increased by 14%. As a result,decomposition sped up. The results high-light the critical connection between thecanopy and the ground, says Pregitzer.

More labs with a view

Körner now wants to help carry out larger-scale experiments with several cranes and toreplicate the carbon dioxide work around theworld in different forest types. About adecade ago, fellow forest ecologists created

the International Canopy Network, whichnow includes more than 750 researchersfrom 62 countries. In the mid-1990s, the U.S.National Science Foundation (NSF) funded acanopy-research database that has fosteredbetter collection, storage, analytical, andvisualization techniques, including three-dimensional representations of the data.

The 4-year-old GCP, which is comple-mentary to the International Canopy Net-work, is building on this momentum. Ithopes to develop a more global view of bio-diversity and climate change effects by dou-bling the number of existing cranes. Most ofthe new cranes proposed by GCP would beerected in tropical forests. Brazil, Ghana,Madagascar, India, and Malaysia havealready signed on to host these so-calledwhole forest observatories.

The key, of course, is finding the money.Over the past decade, only about $4.5 mil-lion a year has been spent on canopy workworldwide. Coming up with $17 millionover the next 5 years would pay for five of

the 10 new observatories called for by GCP.The goal is to have the whole program upand running by 2020. In March, the UnitedNations Environment Program endorsedGCP’s proposal, although to date it has onlygiven GCP $30,000.

To qualify for the next level of UnitedNations support—about $500,000 fordesigning the sites—GCP must come upwith $1 million. The five countries tabbedfor whole-forest observatories have prom-ised to help fund infrastructure and some ofthe research. The rest of the money mustcome from funding agencies of other gov-ernments or private foundations, says GCPhead Andrew Mitchell.

The only U.S.-based crane canopy site, inWind River, Washington, is supported by theNational Forest Service (NSF). NSF also pro-

vides grants to individual canopy scientists,who pay a “bucket fee” of $185 a day. And theU.S. Department of Energy has a big projecton climate change at the Wind River site.

The uncertain financial picture for GCP’splan isn’t preventing some hosts of the newwhole-forest observatories from forgingahead. The Indian government has providedthe Ashoka Trust with seed money to start acanopy program in western India, and lastweek, researchers held a planning meeting.Canopy researchers elsewhere are tweakingtheir activities to conform with the whole-forest observatories protocols.

Thanks to these efforts, “the focus oncanopy research will change from the more-or-less isolated investigations to globallycoordinated projects with comparable meth-ods,” says Martin Unterseher of the Univer-sity of Leipzig, Germany. This integration isessential, he adds, if scientists hope to everunderstand the relationship between forestbiodiversity and global change.

–ELIZABETH PENNISI

www.sciencemag.org SCIENCE VOL 309 26 AUGUST 2005 1315

Canopy cranes operating now

Planned whole forest observatories

Global Canopy Research Network

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Lofty goal. Placing cranes in new places will fill out the network of existing crane research plots and lead to betterintegration of canopy studies.

Published by AAAS