oughton, Mich.-A multi-disciplinary
team of 17 scientists from universities in Michigan, Wisconsin, Minnesota
and Mississippi, as well as the Brookhaven National Laboratory and the U.S.
Forest Service, are building an experimental facility near Rhinelander,
Wis., 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," said project
leader David Karnosky, a geneticist at the Michigan Technological University
School of Forestry and Wood Products.
Karnosky, along with Jud Isebrands of the U.S. Forest
Service, George Hendrey of Brookhaven National Laboratory and Kurt Pregitzer
of Michigan Tech comprise a steering committee that is spear-heading the
project. Scientists from the University of Michigan, University of Wisconsin
and the University of MinnesotaDuluth are also participating in the
study.
Karnosky said 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 as rate of 1 percent to 2 percent annually.
"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 said.
"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 know, 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 can lead to confusing results, since the test plots have
been small. The subtle responses seen as insignificant in the short-term
may compound over several years, he said.
"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," Pregitzer said.
"The system we're constructing at Rhinelander, Wis., 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 measuring 30 meters in diameter. Each ring will
be planted with Aspen throughout, with one-third of each ring having Maple
mixed with Aspen and one-third having Birch mixed with Aspen. More information
is needed on these species because Aspen, Birch and Maple make up 70 percent
of pulpwood harvested in the Great Lakes states.
"In the past, this type of testing took place in
open-top chambers that were only three to four meters in diameter,"
Karnosky said. "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 eco-system response to the combined effects of
elevated carbon dioxide and ozone."
He said that when the system goes into full operation
around July 1, 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 at 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 than anything that's been done previously," Karnosky said.
"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 U.S. Department
of Energy totaling more than $1 million and a $251,000 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.
A worker tests the dispersal system. |
This arrangement of posts and pipes is one of the experimental test rings at the test site near Rhinelander, Wis. |