Tropical Trees 'Fix' Themselves After Being Logged or Cleared: Capturing Nitrogen

Tropical forests may be making a comeback, and it could be their own doing. Scientists have discovered that trees "turn up" their ability to capture nitrogen from the air and release it into the soil as the forest makes a comeback after being logged or cleared for agriculture. The findings have huge implications for forest restoration projects and the ability to mitigate global warming.

In order to examine how trees and forests recover in the face of clearing activities, the researchers examined a square mile of the Panama Canal watershed. There, the scientists compared land-use options as they measured carbon storage, runoff and biodiversity. This allowed them to discover how mature tropical forests, native trees in forest restoration plots and abandoned pastureland compared.

"This is the first solid case showing how nitrogen fixation by tropical trees directly affects the rate of carbon recovery after agricultural fields are abandoned," said Jefferson Hall, one of the researchers, in a news release. "Trees turn nitrogen fixation on and off according to the need for nitrogen in the system."

After examining the trees and the different areas, the scientists discovered something interesting. It turned out that tree species that fixed nitrogen from the atmosphere put on carbon weight up to nine times faster than their non-fixing neighbors during early stages of forest recovery. In fact, nitrogen-fixers provided enough nitrogen fertilizer in the soil to help with storage of about 50,000 kilograms of carbon per hectare during the first 12 years of growth.

"Diversity really matters," said Sarah Batterman, the first author of the study, in a news release. "Each tree species fixes nitrogen and carbon differently so species important at 12 years drop out or become less common at 30 years. You can really see how different players contribute to the development of a mature tropical forest and the ecosystem services in provides."

The findings are huge when it comes to carbon storage. If trees could grow and store carbon, they could essentially turn into a carbon sink, which could have major implications for halting the tide of climate change.

The findings are published in the journal Nature.