Joseph Castro LiveScience.com Yahoo News 13 Jul 12;
When species lose their natural habitat to deforestation and other causes, they don't immediately disappear. Instead, they gradually die off over several generations, racking up an "extinction debt" that must eventually be paid in full. New research shows that the Brazilian Amazon has accrued a heavy vertebrate extinction debt, with more than 80 percent of extinctions expected from historical deforestation still impending.
While the results are alarming, this deathly time lag provides a conservation opportunity to save some of the disappearing species, scientists said, stressing that actions taken in the next few years are critical.
"Now that we know where the extinction debt is likely to be, we can go to the ground to restore habitat and take remedial actions to try to regenerate new habitats," said study lead author Robert Ewers, an ecologist at Imperial College London in the U.K. "We can try to put off ever having to pay that debt."
Extinction debt
The Brazilian Amazonis home to about 40 percent of the planet's tropical forests and a staggering amount of biodiversity. However, the Amazon's plant and animal species are under threat by deforestation, mostly due to agriculture and cattle ranging. [Stunning Photos of the Amazon]
Ewers and his colleagues set out to determine how many species would be lost from at least part of their historical habitats in the Amazon because of past and future deforestation. They began by looking at the "species-area relationship," a well-established ecological pattern describing how the number of species in a given habitat increases predictably as the habitat area increases. By turning this idea on its head, you can figure out how many species should go extinct as their habitat shrinks.
The researchers modeled the number of vertebrate species expected to go extinct within 31-mile by 31-mile blocks (50 by 50 kilometer blocks). They used a combination of deforestation data spanning back to 1970 and species-distribution maps of the Amazon. They compared their model's predictions with the actual number of extinctions seen thus far in the forest regions and found that 80 to 90 percent of the expected local extinctions have yet to happen, and many of them will occur in the southern and eastern regions of the Amazon.
Next, Ewers and his team used their model to estimate the magnitude of the local extinctions and extinction debts expected to occur in four scenarios, which mainly differ in their projections of future deforestation rates. Under the most likely scenario, every forest block will lose an average of about nine vertebrate speciesand be in debt for another 16 species by 2050.
And in all scenarios, species will continue to go extinct more than three decades after deforestation in the Amazon has stopped, if key forest areas are not restored, the researchers found.
"What we've seen in the last four decades is nothing like what we are going to see in the next four decades," Ewers told LiveScience.
Defaulting on the debt
Thiago Rangel, an ecologist at the Federal University of Goiás in Brazil who wasn't involved in the research, was surprised to see the Amazon's huge extinction debt. "Of course, that gives Brazil a very good opportunity for conservation measures," Rangel said. [10 Species You Can Kiss Goodbye]
Rangel, who wrote a perspective article accompanying the study published July 13 in the journal Science, pointed out that Brazil has made a lot of progress in reducing deforestation in the last decade. Moreover, the county has been expanding its network of protected areas — more than 50 percent of the Amazon is now under some form of environmental protection.
"But we are in the middle of a strong transition in Brazil from a very good and modern environmental legislation to something else," Rangel told LiveScience. Agricultural businesses, for example, have been lobbying for weaker forest protection codes — this past May, Brazilian President Dilma Rousseff vetoed portions of such a bill, though this isn't likely the end of the debate, Rangel said.
Rangel stresses that Brazil must "default on its extinction debt," possibly by creating more conservation areas, particularly in places that have been abandoned by agriculturalists. Whatever the case, something needs to be done soon, he said.
Ewers agreed. "This problem has been building, and it will soon roll over and crash like a wave," he said.
Amazon's doomed species set to pay deforestation's 'extinction debt'
Ending forest clearance would not save some species from the effects of decades of destruction, scientists find
Ian Sample guardian.co.uk 12 Jul 12;
The destruction of great swaths of the Brazilian Amazon has turned scores of rare species into the walking dead, doomed to disappear even if deforestation were halted in the region overnight, according to a new study.
Forest clearing in Brazil has already claimed casualties, but the animals lost to date in the rainforest region are just one-fifth of those that will slowly die out as the full impact of the loss of habitat takes its toll. In parts of the eastern and southern Amazon, 30 years of concerted deforestation have shrunk viable living and breeding territories enough to condemn 38 species to regional extinction in coming years, including 10 mammal, 20 bird and eight amphibian species, scientists found.
The systematic clearance of trees from the Amazon forces wildlife into ever-smaller patches of ground.
Though few species are killed off directly in forest clearances, many face a slower death sentence as their breeding rates fall and competition for food becomes more intense.
Scientists at Imperial College, London, reached the bleak conclusion after creating a statistical model to calculate the Brazilian Amazon's "extinction debt", or the number of species headed for extinction as a result of past deforestation. The model draws on historical deforestation rates and animal populations in 50 by 50 kilometre squares of land.
It stops short of naming the species most at risk, but field workers in the region have drawn attention to scores of creatures struggling to cope with habitat destruction and other environmental threats.
White-cheeked spider monkeys, which feed on fruits high in the forest canopy, are endangered largely because of the expansion of farmland and road building. The population of Brazilian bare-faced tamarins has halved in 18 years, or three generations, as cities, agriculture and cattle ranching has pushed into the rainforest. The endangered giant otter, found in the slow-moving rivers and swamps of the Amazon, faces water pollution from agricultural runoff and mining operations in the area.
Writing in the journal Science, Robert Ewers and his co-authors reconstructed extinction rates from 1970 to 2008, and then forecast future extinction debts under four different scenarios, ranging from "business as usual" to a "strong reduction" in forest clearance, which required deforestation to slow down 80% by 2020.
"For now, the problem is along the arc of deforestation in the south and east where there is a long history of forest loss. But that is going to move in the future. We expect most of the species there to go extinct, and we'll pick up more extinction debt along the big, paved highways which are now cutting into the heart of the Amazon," Ewers told the Guardian from Belém, northern Brazil.
Under the "business as usual" scenario, where around 62 sq miles (160 sqkm) of forest are cleared each year, at least 15 mammal, 30 bird and 10 amphibian species were expected to die out locally by 2050, from around half of the Amazon. Under the most optimistic scenario, which requires cattle ranchers and soy farmers to comply with Brazilian environmental laws, the extinction debt could be held close to 38 species.
Ewers said the model reveals hotspots in the Brazilian Amazon where conservation efforts should be focused on the most vulnerable wildlife. "This shows us where we are likely to have high concentrations of species which are all in trouble, and that becomes a way for directing our conservation efforts. We are talking about an extinction debt. Those species are still alive, so we have an opportunity to get in there and restore the habitat to avoid paying that debt," Ewers said.
The Brazilian Amazon is home to 40% of the world's tropical forest and one of the most biodiverse regions on the planet. About 54% of the area is under environmental protection, and in the past five years, stricter controls and better compliance have driven deforestation rates down to a historical low.
The trend towards less deforestation might not last though. Under pressure from the financial crisis, the Brazilian government has proposed a rapid development programme in the Amazon to fuel the economy. The move foresees the construction of more than 20 hydroelectric power plants in the Amazon basin and an extensive push into the rainforest.
Environmentalists are further concerned about an overhaul to Brazil's Forest Code, which is widely expected to weaken the protection of the rainforest, and potentially speed up deforestation once more, according to an accompanying article in Science by Thiago Rangel, an ecologist at the Federal University of Goiás in Brazil. "Extinction debts in the Brazilian Amazon are one debt that should be defaulted on," he writes.
Reducing the rate that extinction debts build up is not enough to preserve the Amazon's biodiversity, Rangel argues. "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.
