Human induced nitrogen deposition is indirectly "fertilizing" forests, increasing their growth and sequestering major amounts of carbon, a joint study by scientists from 10 universities in the US, Canada and Europe, has revealed. Researchers say the findings paint a more complex view of the carbon cycle in forests.
Earlier it was known that logging or other stand-replacement events, whether natural or human induced, 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.
But till now, scientists had never quantified the effect of continuous low levels of nitrogen deposition. As such, the new study could offer a viable solution to the increasing amount of greenhouse gases into the atmosphere, they said.
The study analyzed the carbon balance across a network of forest sites that represented nitrogen deposition in most of Western Europe and continental United States.
Till now, it had 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, and a co-author of the study.
"Through our forests, fertilization by nitrogen deposition is to some degree offsetting our carbon dioxide emissions - at least right now. The results demonstrate that mankind is ultimately controlling the carbon balance of temperate and boreal forests, either directly through forest management or indirectly through nitrogen deposition," she said. The findings appear in the journal Nature.