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Peering into the future with scientific arson

Scientists are setting fires in the Amazon to figure out how encroaching agriculture and climate change will affect forests.

At the forest’s edge, the first 200 yards have been invaded by a mat of grasses, introduced species that migrated in from abandoned pastures.

One of the questions the researchers hope to answer this year is how the behavior of the fire will change now that part of the forest floor is covered with highly flammable grass. The supposition is that the controlled blazes have started a cycle that will continue to feed itself. “Grass promotes fire, and fire promotes grass,” Balch said.

The Woods Hole research is also relevant in the context of a much more critical cycle: between the planets’ forests and the changing of its climate. Tropical forests such as the Amazon are important reservoirs of carbon, and their felling, whether by chain saw or by fire, are among the largest contributors to global greenhouse gas emissions. When deforestation is taken into account, the world’s third and fourth largest emitters are Indonesia and Brazil.

It doesn’t take much to release the forest’s carbon into the atmosphere. During the first blaze in 2004, Balch and her colleagues estimated that each hectare (about 2.5 acres) of burning leaves and saplings produced 22 tons of carbon, or about four times what the average American produces in a year. This year’s fire, which will likely burn many of the fallen logs, is expected to produce more. Yet deforestation is not just a cause of climate change, it’s also a likely result. Computer models of the earth’s climate predict that rising global temperatures will cause the Amazon Basin to become hotter and dryer. In a process known as savannization, lush tropical forest will give way to savannah.

The transformation is predicted to be caused simply by the changing climate, but the research plots show that the process could easily be accelerated when global warming works in conjunction with forest blazes.

“Huge areas can burn when it is dry,” Balch said. “The change can happen much faster if fire is in the mix.”

During the El Nino years of 1997 and 1998, when the Amazon area experienced conditions that would be consistent with climate change, fires swept through large swaths of the forest. Twice as much of the Amazon was degraded that year by forest fires as is cut down during an ordinary year.

Taking account of emissions from deforestation promises to be one of the biggest challenges in the ongoing international climate change negotiations. Balch and her colleagues hope that if the world decides to put a halt to the degradation of the forests, their work will show how and when trees can be vulnerable to fire and what can be done about it.

By burning one patch of forest, they’re hoping to help save the rest.