Deforestation in the Amazon rainforest may capture most of the headlines, but NASA scientists have found a previously-undiscovered killer lurking under the tree tops: understory fires. The extent of damage caused by these fires is so great that it has destroyed more of the Amazon in recent years than deforestation.
These understory fires have escaped NASA's satellites throughout the years because they are hidden from view and all that escapes through the thick tree canopies are wisps of smoke. The team of researchers had to utilize new techniques when analyzing satellite data.
"Amazon forests are quite vulnerable to fire, given the frequency of ignitions for deforestation and land management at the forest frontier, but we've never known the regional extent or frequency of these understory fires," said Doug Morton of NASA's Goddard Space Flight Center in Greenbelt, Md.
According to the study, understory fires between 1999 and 2010 ravaged 2.8 percent of the Amazon, or 33,000 square miles of forest. While grasses and shrubs in the Amazon savannah can handle fires that can spread up to 330 feet per minute, the trees and plants underneath the thick forest canopy cannot. Understory fires burn at a slow rate of only a few feet per minute, but destroy 10-50 percent of the burn area's trees. A slow but efficient killer of the forest.
The study also found no correlation between deforestation for farmland done through burning and understory fires. The highest rates of destruction done by the understory fires were in 2005, 2007, and 2010, while the most prolific years for manmade deforestation were 2003 and 2004.
"You would think that deforestation activity would significantly increase the risk of fires in the adjacent forested area because deforestation fires are massive, towering infernos," Morton said. "You make a bonfire that is a square kilometer in size, throwing ash and live cinders and preheating the adjacent forest. Why didn't we have more understory fires in 2003 and 2004, when deforestation rates were so high?"
The scientists are hoping the study will help drive further research into the way climate change is contributing to understory fires. The existence of these understory fires changes the way carbon emissions from rainforests should be looked at.
"We don't yet have a robust estimate of what the net carbon emissions are from understory fires, but widespread damages suggest that they are important source of emissions that we need to consider," Morton said.
You can read the full published study in the journal Philosophical Transactions of the Royal Society B.