Chain saws scream in a northern Michigan forest, but it's not the familiar sound of lumberjacks. This time the tree killers are environmental researchers. They hope that years from now the aspens they remove will be replaced with a healthy mix of maples, oaks, beeches and pines - which should soak up more carbon dioxide from an ever warmer world.
The scientists hope to take a 100-acre section of the University of Michigan Biological Station research forest closer to the state it was in before logging, when it was dominated by different species of trees instead of the present-day aspens.
They say the experiment is the first they're aware of that involves removing large numbers of trees to promote growth of other species that will boost carbon absorption. It comes as governments and businesses around the world look for economically feasible ways to limit climate change.
It seems simple--a diverse woodland of thriving trees makes for a more balanced effort to produce and maintain forests that can better absorb carbon dioxide:
Carbon dioxide makes up more than 80 percent of the human-produced U.S. greenhouse gas emissions that contribute to global warming, the Department of Energy says.
Scientists believe a diverse woodland will hold more carbon because it will be richer in nitrogen and use sunlight more efficiently. Both are key factors in photosynthesis, during which carbon is absorbed, said Christoph Vogel, a University of Michigan forest ecologist.
"We've been managing forests for lumber or pulp, or perhaps as habitat for deer or quail," said project leader Peter Curtis, an Ohio State University forest ecologist. "Many economists think that managing them for carbon will be a fact of life in the not-too-distant future."
The concern that I have is volume. It would take hundreds of thousands of acres of timber in virtually every region of the world where trees grow in order to make a dent in the problem. How much is enough to actually make an effort? How much forest land is available to be groomed in this way? Enough to make a difference?
Skeptics question forests' long-term reliability for sequestering carbon. They can be cut down, burned or destroyed by disease or insects. Also, it's hard to measure their storage capacity, said Jonathan Pershing, climate and energy program director for the World Resources Institute.
"Are you so sure you can tell us how much carbon is saved from your tree? That's the kind of question that makes people dubious about forest management" as a tool for limiting greenhouse gases, Pershing said.
Curtis and Vogel can't say yet how much carbon the new blend of trees will absorb, but they hope to find out.
The 10,000-acre research forest has two steel towers, both more than 100 feet high and roughly a mile apart, with devices that measure carbon dioxide flowing into and out of the trees. The towers transmit air samples to computers that track the data.
[Aerial photo of research area]
The researchers will compare carbon statistics from the woodlands where they've girded trees with data from the woodlands where they haven't. Aspens will remain in the latter area until they die naturally.
It should take seven to 10 years to determine whether the more diverse forest takes in more carbon, Curtis said. If so, the discovery could guide state and federal forest managers and even private landowners interested in using woodlands to fight climate change.