Ongoing deforestation and fragmentation of forests in the Amazon help create tinderbox conditions for wildfires in remnant forests, contributing to rapid and widespread forest loss during drought years, according to a team of researchers.
The findings show that forests in the Amazon could reach a "tipping point" when severe droughts coupled with forest fires lead to large-scale loss of trees, making recovery more difficult, said Jennifer Balch, assistant professor of geography, Penn State.
"We documented one of the highest tree mortality rates witnessed in Amazon forests," Balch said. "Over the course of our experiment, 60 percent of the trees died with combined drought and repeated fire. Our results suggest that a perfect firestorm, caused by drought conditions and previous fire disturbance, crossed a threshold in forest resistance."
Balch noted that climate change is expected to warm the air in the Amazon region by several degrees and substantially reduce regional precipitation, making understanding the interactions between droughts and fires even more important. "However, even before any prediction of Amazon climate warming occurs, our study demonstrates that drought and fire are already driving forest dieback," she said.
The eight-year study is the largest and longest-running fire experiment in tropical forests. The team of researchers burned 50-hectare forest plots in the southeastern Amazon, a region prone to the effects of climate change.
The plots were burned every year, every three years or not at all. The timeframe for the study included 2007, a year of severe drought. By comparing the tree deaths for the plots each year, the researchers could assess the effect of drought on fire intensity and tree deaths.
"Drought causes more intense and widespread fires," said lead author Paulo Brando, Instituto de Pesquisa Ambiental da Amaznia, Carnegie Institution for Science and Woods Hole Research Center. "Four times more adult t
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