Magazine article Science News

Amazon Forests Caught in Fiery Feedback

Magazine article Science News

Amazon Forests Caught in Fiery Feedback

Article excerpt

One little fire inching through a tropical forest may not kill much. Yet it triggers a vicious cycle--fires preparing the way for bigger fires--that could ultimately turn Amazon jungles into savannas, according to new research.

During a typical 16-day dry spell, only some 5 percent of an intact rain forest dries out enough to catch fire, says Mark A. Cochrane of the Woods Hole (Mass.) Research Center. But even a small fire can sufficiently tatter the shade canopy --and leave behind enough extra debris for fuel--to render some 50 percent of that forest vulnerable to a second, more destructive blaze during a subsequent dry spell. As fires recur, virtually all the forest becomes susceptible, report Cochrane and Mark D. Schulze of Pennsylvania State University in State College.

Brazil's Tailandia region in Para has already slipped into this fiery feedback loop, observe Cochrane and Schulze in the October Conservation Biology.

A decade ago, Tailandia was the new Amazonian frontier. Settlers moved in, and accidental fires became common. Now, forests there that have previously caught fire reburn about every 3 years, too quickly to allow regeneration. Historically, the time between forest fires was at least 400 years.

"Fire is burning everything and everyone," Cochrane says. On a data-gathering trip last December, he found that fire had destroyed even the Brazilian forest service's sustainable management plot.

The first fire that attacks an intact Amazon forest looks "unimpressive," admits Cochrane. Most of the time, the flames spread as a thin ribbon barely ankle-high, creeping perhaps 100 meters a day. These fires take the night off, winking out around 5 p.m. and reigniting from smoldering sparks when the next day heats up around 10 a.m. They kill thin-skinned young trees but typically leave 90 percent of the forest's biomass alive. …

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