The study also is providing insights into the role forests may play in global climate change.

The scientists are finding that carbon dioxide and ozone dramatically alter tree growth, says Eric Kruger, a University of Wisconsin-Madison forest ecologist participating in the project. The gases also may change forest ecology and diversity in the long term.

Carbon dioxide is increasing around the world. It is the gas primarily responsible for the "greenhouse" effect and global warming. Ozone levels also are rising. Elevated ozone levels are now common across much of the eastern United States. Increases in both gases can be traced to our reliance on fossil fuels.

Experts predict that concentrations of these gases will double in the next 100 years, with high ozone levels spreading over much of Wisconsin. The forest scientists are studying how quaking aspen, paper birch and sugar maple -- major components of the forests that blanket almost half of Wisconsin -- will respond to the levels of carbon dioxide and ozone expected in the north by 2050.

Scientists already know that carbon dioxide acts like a fertilizer, stimulating plant growth, while ozone harms plants. But they didn't know what would happen with both gases in a realistic, long-term study.

"Our results have been remarkably consistent," says Kruger. "They show that high carbon dioxide increases the growth of young aspen and birch, high ozone decreases their growth, and the gas's effects on growth cancel each other out when both are elevated."

"Before this study, our understanding of how carbon dioxide and ozone affected trees was based largely on exposing small plants to one or another of the gases for a short time in a greenhouse or growth chambe
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Contact: Richard Lindroth
lindroth@entomology.wisc.edu
608-263-6277
University of Wisconsin-Madison
12-Jun-2002