The Amazon Rainforest Is Burning: Drought-Related Fire Sharply Increases Tree Deaths
The Amazon rainforest has no natural defense to fire because for thousands of years it never needed one. The canopy kept things cool and dark, and lightning almost always comes during a downpour.
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But by 1992, use of slash-and-burn agriculture tactics was begining to accelerate, turning pristine forest to smoldering ash. That was bad enough for the local environment. But then last year, NASA satellite images revealed evidence of a devastating side effect of slash-and-burn. Uncontrolled fires were creeping into the underbrush around deforested areas, killing trees for thousands of square miles. Nearly 3 percent of the Amazon rainforest had been destroyed this way.
Now a team of scientists from Woods Hole Research Center is building on the NASA data by testing how longer dry seasons caused by climate change will affect tree mortality. Fire, they found, will test rainforest endurance far more than previously thought. "None of the models used to evaluate future Amazon forest health include fire," said co-author Michael Coe in a statement announcing the findings, which appear Monday in Proceedings of the National Academy of Sciences. "Most predictions grossly underestimate the amount of tree death and overestimate overall forest health."
NASA's Earth Observatory has been monitoring rainforest fires for more than a decade. What they've discovered is that controlled forest fires designed to clear land for agriculture and add nutrients to the soil frequently get out of control. Small side fires sneak off into the surrounding understory and spread. "Agricultural development has created smaller forest fragments," said Marcia Macedo, of Woods Hole. "These fragmented forests are more likely to be invaded by flammable grasses, which further increase the likelihood and intensity of future fires."
That's the key difference between forest fires in the American West and fires in the Amazon. In the West, fires consume everything and raise the forests' natural fire resistance. In the Amazon, they don't rage; they smolder. It's enough to kill trees and poke holes in the canopy, letting sunlight in and raising the likelihood of more fires. Fire makes the Amazon more flammable.
Recently, the United Nations attributed prolonged drought in Northeastern Brazil to climate change. According to Woods Hole, climatologists are predicting shorter, more intense rainy seasons and longer dry seasons. And that's why the Woods Hole team has attempted to add drought to the picture.
Until this study, no one had experimented with the effect of climate-related fire on rainforest loss. To measure the effect of drought, they burned 124-acre plots of rainforest over eight years in the southeastern Amazon. "The forest didn't burn much in average years, but burned extensively in drought years," Coe said. "We tend to think only about average conditions but it is the non-average conditions we have to worry about." They believe their findings will add nuance to future studies predicting how much more rainforest we're going to lose.
Above photo courtesy of Shutterstock
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