Amazon fires: Humans make rainforest more flammable

Human disturbances are making the Amazon rainforest more flammable, according to researchers.

This is one of the conclusions of a two-year study of the Brazilian Amazon, which revealed that even protected forest is degraded by human activity.

This activity includes selective logging and forest fragmentation, which increase the likelihood of wildfires.

The findings are published in the journal Nature.

"Rainforests don't normally burn," said lead researcher Prof Jos Barlow, from the Lancaster Environment Centre. "But human activities are making them much more flammable."

Human disturbance is having more of an impact in the Amazon than had been thought

While the Brazilian Amazon is protected from large-scale deforestation, this new study suggests that more effort is needed to safeguard what the scientists called the "hyper-diversity of tropical forests".

This team set out to measure the effects that humans have on the rainforest - no easy feat in a dense landscape of 5.5 million sq km.

They selected 400 plots, on a gradient of forest cover - ranging from pristine to deforested areas.

It took two years to gather data from these sites across the Eastern Amazon - painstakingly measuring population densities of trees, birds and insects.

Crucially, this study examined areas of forest that are protected by the Forest Code - the central policy designed to control deforestation, and requiring landowners in the Amazon to maintain up to 80% forest cover.

"If you can imagine a landscape with 80% forest cover, I think most environmentalists would say that's a very good scenario and you've maintained most of your core habitat there," Prof Barlow told the BBC.

"But what we found was those landscapes only really have 50% of their potential value, because of disturbance in the remaining forest."

Disturbance, he explained, could include selective logging, hunting - "anything that humans do to the forests".

Selective logging, for example, can leave the forest fragmented or punch holes in the canopy, drying out the vegetation below. This, combined with the effects of climate change, is leaving the Amazon much more likely to catch fire.

Another member of the team, Dr Alexander Lees from Cornell University, said that many bird species unique to the Amazon were suffering the most from these effects. These endemic species, he said, "cannot survive in disturbed forests".

The Amazon Rainforest covers 5.5 million sq km and stores more than 100 billion tonnes of carbon

"We need to keep focusing on reducing deforestation," said Prof Barlow, "but we need to think about forest disturbance - how we can monitor it, how we can reduce it, and how we can maintain pristine forest in large blocks as well."

"Immediate action is required to combat forest disturbance in tropical nations," said Silvio Ferraz from the University of Sao Paulo, who was also involved in the study. "This is particularly important in Brazil, which holds up to 40% of the world's remaining tropical forests".

Prof Barlow added: "If we're interested in conserving the life that lives with us on this planet today, then we need to conserve these systems."

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