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Fears over Amazon 'extinction debt'

A large "extinction debt" is building up in the Brazilian Amazon that could see the loss of dozens of forest species by the year 2050, say scientists.

More than 80% of the local vertebrate extinctions expected from past and current deforestation have not yet occurred, according to the research. Animals set on the path of extinction by loss of habitat can take several generations to disappear.

In the Amazon rainforest, this process is still at an early stage. But a new prediction model suggests that the "extinction debt" is rapidly accumulating.

Dr Robert Ewers, from Imperial College London, and a team of British and US scientists reconstructed the extinction patterns of the Brazilian Amazon from 1970 to the present day. They then used a mathematical technique to predict how species will fare by 2050 under four different deforestation scenarios.

The model showed that habitat loss over the past 30 years in some eastern and southern areas had already committed eight species of amphibians, 10 of mammals, and 20 types of bird to future extinction.

In the worst case scenario, further deforestation could see at least 10 species of amphibians, 15 of mammals and 30 of birds lost from around half the Amazon.

"Realistic deforestation scenarios suggest that local regions will lose an average of nine vertebrate species and have a further 16 committed to extinction by 2050," the researchers wrote in the journal Science. "There is a window of opportunity to dilute the legacy of historical deforestation by concentrating conservation efforts in areas with greatest debt."

The Brazilian Amazon is the largest continuous forest on Earth, accounting for more than 40% of the Earth's existing tropical rainforest. Significant progress towards protecting the forest has been made in Brazil. Deforestation rates reached a peak of around 28,000 square kilometres per year in the past decade, but now stand at 6,500 square kilometres per year.

If protected areas are expanded and legislation complied with, deforestation rates could fall further and place a cap on the extinction debt, the scientists believe. But a local expert writing in Science warns against complacency, especially with the Brazilian government pushing rapid expansion of infrastructure in the Amazon.

Professor Thiago Rangel, from the Federal University of Goias in Brazil, wrote: "Extinction debts in the Brazilian Amazon are one debt that should be defaulted on. Actions to further decrease the rate of deforestation would help to slow the rate at which additional extinction debt is accumulated. However, reducing the rate at which extinction debts accumulate is not sufficient to preserve the Amazon's biodiversity heritage; the existing extinction debt may eventually lead to the loss of species."

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