Peering into the future with scientific arson

ROME — Scientists will set fire later this month to a small patch of the Amazon forest. A line of flames will crawl across the leaf-covered ground, rip through patches of dry grass and linger over fallen logs — the victims of blazes from previous years.

Following in the fire’s wake will be a phalanx of researchers, measuring temperature and humidity, trying to understand how the forest burns. “The flames are about knee-high,” said Jennifer Balch, who is  the scientist coordinating the blaze for Massachusetts’ Woods Hole Research Center and the Amazon Institute for Environmental Research. “We can actually move around and jump over them. So far, nobody has gotten singed, but by the end of it we’re definitely done with smoke and barbecues.”

The act of scientific arson is an attempt to peer into the future of the Amazon as the encroachment of agriculture and the changing of the climate subject the forest to a new array of stresses.

Charcoal layers in sedimentary deposits in lake beds show that the Amazon has burned in the past, but flames swept through only once every century or two. Recently however, fire has come under increasing use as an agricultural tool. It’s commonly used to clear forests or maintain cattle pastures. Since few measures are put in place to contain the blazes, the forest near ranches and farms can be set aflame every few years. The Woods Hole project is located on the southern stretch of the Amazon Basin in what is known as Brazil’s arc of deforestation, where the agricultural frontier meets the forest. Balch and her fellow scientists have been subjecting research plots there to annual fires since 2004. “The idea is to simulate the extreme fire frequency that is happening in the region,” Balch said.

Unlike forest fires in the United States, where flames rage into the treetops, a fire in the Amazon tends to stay confined to the undergrowth. The larger trees survive. Mid-sized ones can be damaged. Smaller trees, such as saplings, succumb to the flames.

Since the project began, the group has noticed that the number of species present in the undergrowth has dropped by half. Most of the survivors are plants that can resprout from underground roots. Some of the damaged trees have died and fallen. The canopy has begun to open.

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.