May 6, 2017, by Tim Radford
Brazilian researcher Bernardo Flores inspects fire-devastated Amazon forest on the Cuyuni river floodplain. Image: Milena Holmgren/Wageningen University
Increased risk of drought-related wildfires at the heart of the Amazon rainforest adds to vulnerability caused by deforestation at the periphery.
LONDON, 6 May, 2017 – The Amazon rainforest, the greatest and richest of the world’s tropical forests, is vulnerable both from without and within, according to two new studies.
The forested regions in the flood plains at the heart of the Amazon could be more than usually at risk of wildfire that could spread through the rest of the canopy to higher ground.
And although the loss of primary forest has slowed overall in the last 20 years, tree cover is still being lost at the forest’s periphery, as miners, ranchers, growers and loggers continue to degrade secondary forests and woodlands, according to a second study in Science Advances journal.
Everyone expected some attrition at the periphery of the primary forest. But the big surprise is the potential weakness at its heart.
An international team of researchers reports in the Proceedings of the National Academy of Sciences that they matched satellite and field data for the entire Amazon basin, compared forest resilience in those places that were often flooded and never flooded, and analysed the distribution of trees across the river basin.
They found that fire-related savanna dominated the flooded parts when rainfall dropped below 1,500 mm a year. In the upland regions, the forest survived even when rainfall dropped to 1,000 mm a year.
“Our findings suggest that if the Amazonian climate becomes drier, forests will probably collapse first in the seasonally inundated areas,” says Bernardo Flores, a Brazilian scientist now based at Wageningen University in the Netherlands, who led the study.
The great rainforest is subject to cycles of drought, and during severe episodes the region is less likely to absorb carbon from the atmosphere and more likely to release it − a process that could only accelerate global warming. And this in turn could only bring further hazard to the rainforest.
“If the Amazonian climate becomes drier,
forests will probably collapse first in
the seasonally inundated areas”
It was ravaged by fire after the droughts of 1997 and 2005, and the impact on tree cover and soil fertility was, unexpectedly, more persistent in the floodplains.
These cover about 14% of the basin, but the researchers conclude that “their fires can have substantial cascading effects because forests and peatlands may release large amounts of carbon, and wildfires can spread to adjacent uplands. Floodplains are thus the Achilles heel of the Amazon system.”
Researchers concerned with the rainforest’s importance in the carbon budget still have to factor in the human dimension. Humans have played a role in managing the vegetation for millennia, and economic pressure means that tracts of the forest remain at risk.
Scientists from the University of Maryland in the US looked at data from 2000 to 2013 for the whole vast area of the Legal Amazon Region, an administrative entity that embraces 5 million square kilometres of nine states in Brazil, and is home to 24 million people.
They found that although humans were still invading and clearing primary forest, they were disturbing an even greater area of secondary forest, plantation and woodland.
Altogether, this clearing of regenerated forest and plantation accounted for 53% of gross tree cover loss, the researchers say, and up to 35% of the above-ground carbon released to the atmosphere.
Fire cleared about 9% of the primary forest, with the damage peaking during the droughts of 2005, 2007 and 2010. – Climate News Network
Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.