"That's the story that we all learned for decades in ecology classes," Law said. "But it was just based on observations in a single study of one type of forest, and it simply doesn't apply in all cases. The current data now makes it clear that carbon accumulation can continue in forests that are centuries old."
When an old growth forest is harvested, Law said, studies show that there's a new input of carbon to the atmosphere for about 5-20 years, before the growing young trees begin to absorb and sequester more carbon than they give off. The creation of new forests, whether naturally or by humans, is often associated with disturbance to soil and the previous vegetation, resulting in decomposition that exceeds for some period the net primary productivity of re-growth.
Old growth forests, the study said, continue to sequester carbon for many centuries. And when individual trees die due to lightning, insects, fungal attack or other causes, there is generally a second canopy layer waiting in the shade to take over and maintain productivity.
One implication of the study, Law said, is that nations with significant amounts of old forests may find it somewhat easier to offset greenhouse gas emissions if those forests are left intact. It will also be necessary, she said, for land surface models that attempt to define carbon balance to better characterize function of old forests.
Many of the conclusions from the study were based on data acquired from the AmeriFlux and CarboEurope programs, researchers said. Multiple funding sources included the U.S. Department of Energy, CarboEurope, the European Union, and others. Authors were fr
|Contact: Beverly Law|
Oregon State University