Fires are transforming the Amazon rainforest into savanna

Savanna is taking over parts of the Amazon rainforest as a result of recurring forest fires, according to a new study published in the journal Ecosystems. The researchers, led by Bernardo Monteiro Flores of UFSC, investigated the impacts of wildfires on vegetation and soil quality over the last four decades. 

The study revealed that the future of the rainforest is greatly threatened by fire activity, even in well-conserved areas that are unaffected by deforestation.

“The edges of the Amazon Rainforest have long been considered the most vulnerable parts owing to expansion of the agricultural frontier. This degradation of the forest along the so-called ‘deforestation arc’ (a curve that hugs the southeastern edge of the forest) continues to occur and is extremely troubling,” Flores told Agência FAPESP.

“However, our study detected the appearance of savannas in the heart of the Amazon a long way away from the agricultural frontier.” 

The research was focused on an area of floodplains surrounding the middle Negro River near Barcelos, where areas of white-sand savanna are expanding. The experts blame this expansion on the increasing frequency and severity of wildfires associated with climate change. 

“We mapped 40 years of forest fires using satellite images, and collected detailed information in the field to see whether the burned forest areas were changing,” said Flores. 

“When we analyzed tree species richness and soil properties at different times in the past, we found that forest fires had killed practically all trees so that the clayey topsoil could be eroded by annual flooding and become increasingly sandy.”

The researchers also determined that, as burned floodplain forest recovers, there is a major shift throughout the vegetation in which native herbaceous cover expands, forest trees disappear, and white-sand savanna tree species become dominant.

According to Flores, white-sand savannas are part of the Amazon ecosystem, covering about 11 percent of the biome. The seeds of savanna plants are distributed by water, fish, and birds, and are more likely to germinate when they reach a burned area with degraded soil than forest species.

“Our research shows native savanna cover is expanding and may continue expanding in the Amazon. Not along the ‘deforestation arc,’ where exotic grasses are spreading, but in remote areas throughout the basin where white-sand savannas already exist,” said Flores.

The researchers emphasized that the Amazon floodplain forest is far less resilient than upland terra firma forest – burning more easily and degrading more quickly.  

“Floodplain forest is the ‘Achilles heel’ of the Amazon,” said study co-author Professor Milena Holmgren. “We have field evidence that if the climate becomes drier in the Amazon and wildfires become more severe and frequent, floodplain forest will be the first to collapse.”

A drier climate and more frequent fires have already arrived in the Amazon. The researchers found that during the severe 2015-16 El Niño event, wildfires in the middle Negro area burned down an area seven times larger than the total area destroyed by fire in the preceding 40 years.

“The additional loss of floodplain forest could result in huge emissions of carbon stored in trees, soil and peatlands, as well as reducing supplies of resources used by local people, such as fish and forest products,” said Flores.

“The new discoveries reinforce the urgency of defending remote forest areas. For example, a fire management program should be implemented to reduce the spread of wildfires during the dry season.”

The study is published in the journal Ecosystems.

–—

By Chrissy Sexton, Earth.com Staff Writer