The study, to be posted the week of Aug. 4 on PNAS Online, is based on a two-year field experiment conducted in the grassy foothills above Stanford's main campus. Instead of causing the soil to dry up, the experiment revealed that higher temperatures actually increased soil moisture by as much as 10 percent.
"Warming accelerates evaporation, so we expected warmer to mean drier," said lead author Erika S. Zavaleta, a former Stanford doctoral student now on the faculty of the University of California-Santa Cruz. "We were surprised to find that warming actually increased moisture in our grassland plots during those critical weeks in late spring at the end of the growing season, when moisture shapes which plant species prevail. We traced this unexpected moisture increase to the plants themselves."
The study adds to a growing body of knowledge about the major role that plants can play in global warming, added co-author Christopher B. Field, a professor by courtesy of biological sciences at Stanford and director of the Carnegie Institution's Stanford-based Department of Global Ecology.
"We found that, once the plants shut down, the moisture is effectively trapped in the soil," he noted.
Global Change Experiment
The PNAS study is the third in a trilogy of papers published in the last eight months by the Jasper Ridge Global Change Project. This multiyear experiment is designed to demonstrate how grassland ecosystems will respond to global changes that could occur in the next 100 years if increased fossil fuel consumption
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Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
4-Aug-2003