Water efficiency in the forest

Peter Reuell in the Harvard Gazette: Spurred by increasing levels of atmospheric carbon dioxide, forests over the past two decades have become dramatically more efficient in how they use water, a Harvard study has found.

Studies had long predicted that plants would begin to use water more efficiently as atmospheric carbon dioxide levels rose. But a team led by research associate Trevor Keenan and Andrew Richardson, assistant professor of organismic and evolutionary biology, has found that forests around the world are becoming more efficient than expected.

Using data collected from forests in the northeastern United States and around the world, Keenan and Richardson found greater increases in efficiency than those predicted by even the most state-of-the-art computer models. The work, which was done in collaboration with researchers from Harvard’s Department of Earth and Planetary Sciences, the U.S. Forest Service, Ohio State University, Indiana University, and the Karlsruhe Institute of Technology in Germany, is described in a July 10 paper in Nature.


“This could be considered a beneficial effect of increased atmospheric carbon dioxide,” said Keenan, the first author of the paper. “What’s surprising is we didn’t expect the effect to be this big. A large proportion of the ecosystems in the world are limited by water. They don’t have enough water during the year to reach their maximum growth. If they become more efficient at using water, they should be able to take more carbon out of the atmosphere due to higher growth rates.”

While increased atmospheric carbon dioxide may benefit forests in the short term, Richardson emphasized that the overall climate picture would remain grim if levels continue to rise...

Public domain shot of a tree canopy by Steve Hillebrand, US Fish and Wildlife Service