In the drought-stricken El Nino years of 1997 and 1998, small fires associated with farming and logging triggered raging fires in the rain forests of Southeast Asia and the Amazon. Their unprecedented severity shocked residents and researchers alike. Now, Mark A. Cochrane and his colleagues at the Woods Hole Research Center in Massachusetts have identified the mechanism that caused those fires to blaze out of control.
In a tropical rain forest, says Cochrane, a low-intensity fire creates more fuel than it consumes, because it kills shrubs and trees without burning them, leaving fuel for later fires. As a result, the next fire may be more than 10 times hotter and can kill even the largest trees. The opposite happens in temperate forests, where periodic fires are an ecological necessity, consuming dry brush that could otherwise fuel larger blazes. To help prevent future conflagrations in tropical forests, Cochrane recommends establishing firebreaks before intentional burns and prohibiting logging near agricultural areas.