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Peter Wyckoff, professor of biology, and Rachel Bowers '03 identify a changing relationship between tree growth, drought, and carbon dioxide

Posted by Judy Korn on Monday, Jan. 4, 2010


By studying bur oak trees in three different west central Minnesota locations, Peter Wyckoff, University of Minnesota, Morris associate professor of biology, and Rachel Bowers ’03 identified a changing relationship between tree growth, drought, and carbon dioxide (CO2). The Journal of Ecology recently published the results of their research, “Response of the prairie–forest border to climate change: impacts of increasing drought may be mitigated by increasing CO2.”

Wyckoff, Bowers, and several other UMM students collected data from trees in Maplewood State Park, Glacial Lakes State Park, and Sibley State Park between 2002 and 2007. Typically, growth rings are larger when trees receive good light, adequate nutrients, and are free from disease. Tree rings are smaller when growing conditions are poor, especially in drought years. Through their study of growth rings, Bowers and Wyckoff found that west central Minnesota oak trees have became less sensitive to drought during the 20th century.

“Scientists have spent many years developing the techniques needed to reconstruct climate via tree rings,” says Wyckoff. “The problem is that in the past few decades, the tree ring-climate relationships seem to have become ‘decoupled’ in many areas. The main cause seems to be increasing atmospheric carbon dioxide, which directly impacts plants. Carbon dioxide fuels photosynthesis, and increased carbon dioxide in the air can both speed-up plant growth and make plants less sensitive to drought.”

Wyckoff notes that stomata, small holes located on the underside of leaves, play a key role in a plant’s ability to withstand drought. Plants open and close stomata to take in carbon dioxide needed for photosynthesis. Plants growing in high levels of carbon dioxide reduce the amount of time their stomata are open, which reduces water loss and susceptibility to drought.

“The concept of ‘water-use efficiency’ is of crucial interest to farmers and foresters alike,” states Wyckoff. “Carbon dioxide causes warming that will likely make west central Minnesota a drier place in the future. At the same time, increased carbon dioxide in the air makes plants growing in our region less susceptible to drought. The balance between these two forces will be crucial.”