Scientists at the University of Michigan say that forests in North American appear to have a greater capacity to absorb carbon dioxide than previously believed, and they now think the forests may be able to slow the pace of global warming.
During a 12-year study at an experimental site in northeastern Wisconsin, microbial ecologist Donald Zak and other colleagues pumped extra carbon into the canopies of trembling aspen, paper birch and sugar maples. Some of the trees also received additional levels of ground-level ozone to simulate the effects of increasing pollution in the future.
The researchers found that trees with higher levels of carbon dioxide grew at an accelerated rate, and their fallen leaves and branches released more nitrogen back into the soil. Zak noted, however, that growth attributed to higher CO2 levels will eventually "hit the wall" and come to halt, although it has not been determined how long that will take.
The trees exposed to higher ozone levels did not grow as fast as other trees, but at the end of the 12-year study, the increased ozone levels had no effect on productivity in the forest. Zak said that ozone tolerant species took up slack of trees that were negatively affected. The same thing happened with trees exposed to higher levels of CO2. The important thing, the scientists said, is that genetic diversity and the composition of plant species in the forests are both important to the ecosystem's response to climate change. As Zak noted, "Biodiversity matters."
(photo: David Karnosky, Michigan Technological University)
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