CORVALLIS, Ore. Human-caused nitrogen deposition has been indirectly fertilizing forests, increasing their growth and sequestering major amounts of carbon, a new study in the journal Nature suggests.
The findings create a more complex view of the carbon cycle in forests, where it was already known that logging or other stand-replacement events whether natural or not create periods of 5-20 years when there is a net release of carbon dioxide from forests to the atmosphere, instead of sequestration as they do later on.
The end result is a highly variable forest carbon cycle that appears to be heavily influenced by the footprint of humans, one way or another. Its a complicated process with powerful driving forces that were poorly understood, said scientists from 10 institutions in the U.S., Canada and Europe.
Until this report, researchers had never quantified the effect of continuous low levels of nitrogen deposition about 5-10 percent of the amount used by a farmer each year - to spur net carbon uptake by forests and actually offset a significant amount of greenhouse gases into the atmosphere.
This broad study analyzed the carbon balance across a network of forest sites that represent nitrogen deposition in most of Western Europe and the continental United States. Until now, it has been difficult to separate the effects of nitrogen deposition on forests from the many other variables that affect their carbon release or sequestration things like forest age, logging, wildfires, disease or insect epidemics, or other causes. This study attempted to do that, and found that the net carbon sequestration by temperate and boreal forests was overwhelmingly determined by nitrogen inputs.
What is surprising is that the net sequestration is quite large for a relatively low level of nitrogen addition, said Beverly Law, a professor of forest science at Oregon State University, co-author of the study and director of the AmeriFl
Contact: Beverly Law
Oregon State University