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Environment: Is the Amazon rainforest near a tipping point?

A NASA photo taken from the International Space Station shows sunlight glinting off the Amazon River.

A NASA photo taken from the International Space Station shows sunlight glinting off the Amazon River.

Drought the main driver of destructive fires

By Staff Report

FRISCO — Longer droughts, land-use changes and wildfires may  be pushing parts of the Amazon rainforest toward an ecological tipping point, a team of scientists said after analyzing the effects of fire in a series of study plots.

The changes may abruptly increase tree mortality and change vegetation over large areas, the researchers said, pointing out that current Amazon forest models don’t include the impacts of wildfires. As a result, projections of future forest health tend to underestimate the amount of tree death and overestimate overall forest health, said Dr. Michael Coe, of the Woods Hole Research Center.

Coe was part of a research team that burned 50-hectare plots of the Amazon during an eight-year experiment to learn how fire frequency and weather conditions affected tree deaths. Drought was the key driver of destructive fires, they found. The forest didn’t burn much in average years, but burned extensively in drought years … We tend to think only about average conditions but it is the non-average conditions we have to worry about,” Coe said.

Climate change is expected to cause shorter more intense rainy seasons and longer dry seasons, with more frequent droughts like those observed in this study. Future simulations of climate in the Amazon suggest a longer dry season leading to more drought and fires.

NASA satellite data provide a regional context for results from the experimental burns. In 2007, fires in southeast Amazonia burned 10 times more forest than in an average climate year, “an area equivalent to a million soccer fields” according to co-author Douglas Morton of NASA. Large portions of Amazonian forests are already experiencing droughts and are increasingly susceptible to fire.

“Agricultural development has created smaller forest fragments, which exposes forest edges to the hotter dryer conditions in the surrounding landscape and makes them vulnerable to escaped fires,” said Dr. Marcia Macedo. “These fragmented forests are more likely to be invaded by flammable grasses, which further increase the likelihood and intensity of future fires.”

“This study shows that fires are already degrading large areas of forests in Southern Amazonia and highlights the need to include interactions between extreme weather events and fire when attempting to predict the future of Amazonian forests under a changing climate,” Macedo concluded.

 

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