Saturday, March 1, 2008

AmeriFlux reveals how forests cycle carbon...

A new article published by OnEarth--the magazine of the National Resources Defense Council--reviews new research into carbon sequestration in older forests. The Giving Trees reports on the AmeriFlux Network, an international collaboration that tracks the exchange of carbon dioxide, water vapor, and energy in the Americas. This research has challenged conventional wisdom about how forests mitigate climate change.

Global warming has forced foresters to address the impact of logging on the flow of carbon between forests and the atmosphere, and many in the industry have insisted that stands of young, fast-growing trees capture carbon more efficiently than do older forests, writes Sharon Levy.

According to a recently developed technology called the eddy covariance method (or eddy flux measurement), it turns out that forests hundreds of years old can continue to actively absorb carbon. “All the ecological models said that temperate forests stop their net carbon uptake at about 50 years. Eddy flux data has clearly shown that this is not true,” states Harvard Forest researcher Steven Wofsy.

Resprouting clear-cuts, on the other hand, emit carbon despite the rapid growth rate of young trees because decomposer microbes in the forest soil--which release carbon dioxide as they break down dead branches and roots--work more quickly after a stand is logged. In this case, the microbes respiring in the soil--rather than photosynthesis by the trees aboveground--can dominate the carbon balance for up to 20 years.