Scientists To Assess Effects Of Ozone, Carbon Dioxide On Trees

December 03, 1996

HOUGHTON, MI-A multidisciplinary team of 17 scientists from universities in Michigan, Wisconsin, Minnesota, and Mississippi, Brookhaven National Laboratory, and the U.S. Forest Service are building an experimental facility near Rhinelander, WI to test the effects of combined ozone and carbon dioxide on forest stands.

"The rise in atmospheric carbon dioxide concentrations is expected to have profound effects on forest vegetation, including changes in the responses of trees to environmental stresses," says Project Leader David Karnosky, a geneticist in the School of Forestry and Wood Products at Michigan Technological University. Karnosky, along with Jud Isebrands of the U.S. Forest Service, George Hendrey of the Brookhaven National Laboratory, and Kurt Pregitzer of Michigan Tech comprise a steering committee that is spearheading the project. Scientists from the University of Michigan, University of Wisconsin, and University of Minnesota-Duluth are also participating in the study.

Karnosky says that in the future many forests will be exposed to increased atmospheric carbon dioxide in conjunction with other pollutants. One of the most important of these is tropospheric ozone, which is increasing globally at a rate of 1 to 2 percent a year.

"While it is known that increasing carbon dioxide increases plant growth, elevated ozone levels have just the opposite effect, decreasing photosynthesis and thereby limiting plant growth," he says. "That's why it's so important for us to find out how trees will respond to increasing amounts of both of these elements in the natural environment."

Until now, the majority of experiments with carbon dioxide and/or ozone have been short-term studies conducted in controlled indoor chambers, greenhouses, or open-top chambers in the field, according to Karnosky. These conditions, he says, can lead to confusing results, since the test plots have been small and subtle responses that may be seen as insignificant in the short term may, in fact, compound over several years.

"There is a recognized urgent need for long-term, forest community level carbon dioxide and ozone exposure studies under more realistic conditions, and a more holistic approach that includes integrated studies of forest productivity and community dynamics," says Pregitzer. "The system we're constructing at Rhinelander, Wisconsin offers an opportunity to study such relationships."

The "system" under construction at Rhinelander will be the largest free air carbon dioxide exposure system in the world. It will include 12 ring-shaped test plots 30 meters in diameter. Each ring will be planted with aspen throughout, with one-third of each ring having maple mixed with the aspen and one third having birch mixed with the aspen. More information is needed on these species because aspen, birch, and maple make up about 70 percent of the pulpwood harvested in the Great Lakes states.

"In the past, this type of testing took place in open-top chambers that were only 3 to 4 meters in diameter," explains Karnosky. "The new plots will allow us to look at a much larger sample of the forest community and get a much more realistic understanding of community dynamics and ecosystem response to the combined effects of elevated carbon dioxide and ozone."

He says that when the system goes into full operation around July 1 of next year, carbon dioxide and ozone will be dispersed into the planted test plots through vertical vented pipes located on the upwind side of the plots. This arrangement will allow the gases to be blown into the plots in a way that will best simulate natural conditions. Scientists from the Brookhaven National Laboratory have designed a computer program to ensure that the amount of each gas released is accurate with respect to the experiment's requirements.

"This study will more closely approximate natural conditions that anything that's been done previously," says Karnosky. "It should provide the information scientists need to determine the ecological consequences of the exposure of forests to elevated carbon dioxide and ozone or its precursors."

The study is being funded by grants from the Department of Energy totaling more than $1 million and a $25,000 equipment grant from the National Science Foundation. The U.S. Forest Service Global Change Program has also contributed more than $400,000 to the project.

Note to editors: Photos of the project are available. Contact Jim Lutzke at 906-487-2343 or e-mail: For more information on the project itself, contact Dave Karnosky at 906-487-2898; e-mail:

Michigan Technological University

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