July 13, 2012

Deforestation Extracting ‘Extinction Debt’ From Amazon Species

Brett Smith for - Your Universe Online

The clearing of the Brazilian rainforest is racking up a debt than won´t be paid by any government, but instead will be paid by the species that become extinct as a result of the destruction of their habitat.

If deforestation and development in the Brazilian Amazon occur at their current rates over the next 40 years, 25 vertebrate species will become locally extinct, according to new research published this week in Science.

Scientists use the term “extinction debt” to describe the future loss of species that could occur as a result of past deforestation of land development. The extinction debt model draws on historical deforestation rates and animal populations in 31-square mile (50 km) plots of land.

“Species do not go extinct immediately when their habitat shrinks, climate changes beyond their tolerance limit, or an invasive species spreads,” explained Thiago Rangel, who was not involved in the research, but wrote an accompanying article in a Science.

“It may take several generations after an initial impact before the last individual of a species is gone.”

Previous studies have not attempted to calculate an exact extinction debt figure and have also assumed that deforestation occurs at a constant rate. In the latest study, the research team accounted for deforestation that tends to occur in fits and spurts.

To calculate how many species may become extinct as a result of deforestation, Robert Ewers, from Imperial College London, along with a team of British and U.S. scientists created a model based on the rates of deforestation throughout the Brazilian Amazon from the 1970s through 2008.

Using previous studies that related habitat loss with the loss of vertebrates, they were able to use the deforestation data to project future extinction rates through 2050. In the worst case of the team´s four modeled scenarios, further deforestation could mean at least 10 species of amphibians, 15 of mammals and 30 of birds would be lost from around half the Amazon.

In the face of the study´s more dire assessments, researchers noted in the study that there is “a window of opportunity to dilute the legacy of historical deforestation by concentrating conservation efforts in areas with greatest debt."

On a more positive note, significant progress towards protecting the forest has been made in Brazil. Deforestation rates reached their peak in the past decade at over 17,000 square miles per year, but now officials calculate the rate at just over 4,000 square miles per year.

Conservationists say if protected areas are expanded and enforced, deforestation rates could fall further and place a lid on the extinction debt. Rangel advises that in addition to protecting the existing Amazon, Brazil should pursue an aggressive reforestation policy.

"The existing debt may eventually lead to the loss of species. To prevent species extinctions, it is necessary to take advantage of the window of opportunity for forest regeneration. Restored or regenerated forests initially show lower native species richness than the original forests they replaced, but they gradually recover species richness, composition and vital ecosystems functions, reducing extinction debt and mitigating local species loss," he writes.