Environment@Harvard

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Volume 3, Issue 1

Environment @Harvard H a r v a rd U n i ve r s i t y C e n t e r f o r t h e E nv i r o n m e n t www.environment.harvard.edu

The Rainmaker In the Amazon, Gauging the Resilience of a Rainforest By Alvin Powell he tower lay on the forest floor, a twisted mess of metal, wires, leaves and branches. Moments earlier, it had stood more than 200 feet high, a thin staff of crisscrossed metal loaded with scientific instruments, poking its nose above even the 160-foot tall trees of Brazil’s Tapajos National Forest, a vast tract of rainforest in the eastern Amazon more than 2,000 square miles in extent. For nearly five years, from 2001 until its collapse in 2006, the tower’s instruments had sampled Amazonian air, measuring the forest’s inhalations and exhalations as it absorbed carbon dioxide during the day, when sunshine drives photosynthesis, and released the gas at night, when photosynthesis shuts down and respiration becomes dominant. For Rotch professor of atmospheric and environmental science Steven Wofsy, the tower had been a scientist’s dream come true. Since the mid-1980s, when he first began tower-based data collection in the regenerating forests of Massachusetts, he had wanted to run similar experiments in the Amazon. An Amazonian tower, he had realized, could collect data in the world’s largest remaining tropical forests, and test hypotheses about the Amazon’s regional functioning and role in global climate. Such hypotheses filled scientific journals, magazines, and later, the weighty reports

of the thousandplus scientist Intergovernmental Panel on Climate Change. Even in its ruin, though, the tower illuminated a key truth about the forest. The Amazon jungle is not a static biological feature, but rather a dynamic, shifting place, responding to inputs from the atmosphere and the soil, reacting to human chainsaws that convert vast tracts to field and pasture and growing new trees and vines in the suddenly sunny spots created by the regular fall of giant trees. “This forest turns over really fast,” says Wofsy. “You have these large trees that… are growing fast, but they couldn’t have been doing so for very long because they’d be even bigger than they are. Then you realize they turn over quickly and they start falling on you and knocking your tower down.” Though the Amazon is always in motion, concerns about a warming globe have raised scientific interest in just how it is changing. The forest covers 2.2 million square miles and contains a large porPhoto courtesy Harvard Magazine

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A research tower in the Amazon rainforest. This one, near Manaus, Brazil, is still standing.

tion of the world’s biodiversity, harboring perhaps one fifth of the Earth’s species of plants and animals. This ecosystem exerts an enormous influence on the land, sea, and atmosphere. The Amazon river alone accounts for 18 percent of all the freshwater that flows into the world’s oceans. The Amazon basin, which receives more than twice the rainfall of the Northeastern United States, is a regional rainmaker: an estimated 30 percent of the rain that falls on the forest comes not from the ocean, but from evaporation from the trees themselves. In addition, a major atmospheric upwelling zone is anchored over the Amazon, pumping energy and water vapor into the

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