Carbon losses caused by forest fires of 2015 and 2016 could be up to four times greater than thought, according to a study of 6.5 million hectares of forest in Brazilian Amazonia.
The research, published in the journal Philosophical Transactions of the Royal Society B, has revealed that the aftermath of 2015 and 2016 forest fires in the Amazon resulted in carbon dioxide (CO2) emissions three to four times greater than comparable estimates from existing global fire emissions databases.
Researchers at the Lancaster University in the UK found that uncontrolled wildfires in the understorey - or ground level - of humid tropical forests during extreme droughts are a large and poorly quantified source of CO2 emissions.
The study looked at a 6.5 million hectare region, of which almost one million hectares of primary and secondary forests burned during the 2015-2016 El Nino, a climate cycle in the Pacific Ocean with a global impact on weather patterns.
Although the area analysed covers less than 0.2 per cent of Brazilian Amazonia, these wildfires resulted in expected immediate CO2 emissions of over 30 million tonnes, three to four times greater than comparable estimates from global fire emissions databases, researchers said.
"Uncontrolled understorey wildfires in humid tropical forests during extreme droughts are a large and poorly quantified source of CO2 emissions," said Kieran Withey of Lancaster University.
"These understory fires completely consumed leaf litter and fine woody debris, while partially burning coarse woody debris; resulting in high immediate CO2 emissions.
"This analysis covers an area of just 0.7 per cent of Brazil, but the amount of carbon lost corresponds to 6 per cent of the annual emissions of the whole of Brazil in 2014," Withey said.
At the end of 2015, Santarem in the Brazilian state of Para, was one of the epicentres of that year's El Nino, researchers said.
The region experienced a severe drought and extensive forest fires and the researchers were working right in the middle of it, they said.
The research team quickly realized they had the opportunity to document in detail how a forest responds to fire on this scale.
Erika Berenguer of Lancaster University and colleagues found that following the fires, the surviving trees grew significantly more than those located in unburned forests, regardless of their history of previous human disturbance.
On average trees in burned areas of forest grew 249 per cent more than trees in forests hit by drought but not fire. Although the growth rate is good news, this large increase in growth appears to be a relatively short-term response, researchers said.
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