"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," Doug Morton, a researcher at NASA's Goddard Space Flight Center in Greenbelt, Md., and the study's lead author, said in the statement. The study, published in Philosophical Transactions of the Royal Society B, demonstrates that, in years with the most understory fire activity, such as 2005, 2007 and 2010, the area of forest affected was several times greater than the area affected by deforestation for expansion of agriculture. Despite this seemingly low-key presence, however, understory fires can damage large areas because Amazon trees are not adapted to fire and the long, slow burn can claim anywhere from 10 to 50 percent of the burn area's trees. But between 1999 and 2010, these forest fires burned more than 33,000 square miles (85,500 square kilometers), an area larger than the state of South Carolina, according to a NASA release. The fires usually occur near inhabited areas, however, and are likely ignited by cigarettes, campfires and other human sources, NASA said.
– Someone flying above the Amazon in a plane would see nothing amiss, but scores of small, slow-moving fires beneath the canopy of trees are destroying more land than deforestation, reports LiveScience. New satellite imaging from NASA has revealed these so-called "understory fires." Flames are only a few feet high, and the fires themselves move only a few feet per minute, but they can last several weeks, reports Nature World News. The culprit? Careless humans, apparently. These fires generally occur near populated areas, and they're often set off by campfires or discarded cigarettes—aided and abetted by low humidity. NASA researchers say the discovery of the fires will affect climate models. "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," says one.