Wesely Award Winner Sees the Forest for its Trees

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Colleen Iversen

Forests have typically been seen as critical to the absorption of excess carbon dioxide or CO2 emissions, but one University of Tennessee graduate student has found that the trees role in taking up excess carbon might be more complicated than once thought.

Colleen Iversen is working on her doctorate in plant ecology at UT. She is also a fellow with the U.S. Department of Energy’s Global Change Education Program, which is managed by the Oak Ridge Institute for Science and Education in Oak Ridge, Tennessee.

Iversen’s research takes place in an experimental sweetgum plantation on property run by Oak Ridge National Laboratory.

Here in the forest, the air has been fumigated with highly concentrated levels of carbon dioxide – in fact, what scientists estimate atmospheric levels to be in the year 2050. This is so that scientists like Iversen can study how the trees and plants respond. With levels of carbon dioxide in the atmosphere increasing at a rapid pace due to fossil fuel burning, Iversen’s research asks important questions about how the excess carbon affects the forest.

“I study forest growth in response to rising concentrations of atmospheric carbon dioxide. And in particular, I look at the way that forests allocate their production in response to the stimulus of carbon dioxide, and this forest in particular has increased root production in lieu of increasing stem root production.”

After extracting cores of soil, Iversen examines the rate of growth of the roots. She also runs experiments to find out how quickly the roots decompose in the soil.

What Iversen has found is that a significant amount of the excess carbon dioxide taken up by the trees is actually increasing the growth of tiny roots.

“In our forest plantation, the trees that are exposed to elevated atmospheric carbon dioxide instead of allocating the extra carbon that they take up to wood, they allocate it below ground to fine roots, and those are roots less than a millimeter in diameter.”

Iversen explains that this response is interesting given what has been the prevailing thought among scientists who study climate change.

“The party line has always been that carbon, or that forests can store carbon, and what we’ve been finding is that in this forest, carbon dioxide has increased forest production but the forest has allocated that new organic matter towards roots.”

These tiny roots grow and decay on a seasonal basis. And so the carbon storage is not long term as it would be if it was stored in the woodier parts of the tree. Long term storage of excess CO2 from fossil fuel burning is essential to helping reduce its contribution to global warming.

In recognition of her research, Iversen won the 2007 Marvin L. Wesely Distinguished Graduate Research Environmental Fellowship, which brings more recognition and visibility to her research. Iversen is on track to finish her doctorate at UT in August 2008.