Amazon forest 'could vanish fast'

The giant Amazon otter is one species that depends on the forest

By BBC News Online's environment correspondent Alex Kirby

The destruction of the Amazon rainforest could be irreversible within a decade, according to a US scientist.

James Alcock, of Pennsylvania State University, says the forest could virtually disappear within half a century.

His estimate of the possible rate of destruction is faster than most others and Mr Alcock, professor of environmental sciences at Penn State's Abington College, says the danger lies in a complex feedback process.

Research published in the journal Science earlier this year suggesting that deforestation rates in the Amazon could reach 42% by 2020 were based on unreliable facts and "ecological futurology", Brazil's science and technology ministry said.

Point of no return

But Professor Alcock's forecast, based on a mathematical model of human-driven deforestation, is starker still.

Without immediate and forceful action to change current agricultural, mining and logging practices, he says, the forest could pass the point of no return in 10 to 15 years.

Human pressures on the forest are growing

And the model indicates that the forest, far from having 75 or 100 years to reach total collapse as other researchers predict, could essentially disappear within 40 or 50 years.

Professor Alcock is presenting his findings at a conference in Scotland being held jointly by the Geology Societies of America and London.

He hopes to develop his research with fieldwork in the Amazon, although he argues that his model is also a useful predictor of what could happen in the other great tropical forest systems, in south east Asia and the Congo river basin in Africa.

Professor Alcock, who says the size of the Amazon river basin has already been reduced by about 25%, believes the threat lies in a process known as evapotranspiration, in which the rain that falls on a forest is retained and then returned to the atmosphere.

But without a healthy vegetation base, he says, there is little to stop the water running off, and this creates the potential for a highly unstable forest system.

Risks are close

"Because of the way tropical rainforests work, they are dependent on trees to return water to the air", he said.

"This interdependence of climate and forest means risks to the forests are much closer at hand than we might expect.

"It's a very difficult problem because of several pressures. For example, you can't say: 'Leave the rainforests alone' when people are living in poverty."

Forest loss leaves little in its wake

Professor Alcock says plans to preserve small areas of forest would probably not work, because damage to the overall system would limit the rain necessary for their survival.

Less rain falling on the forest could also increase the likelihood of fires.

Another consequence he foresees is the extinction of many creatures that depend on the forest for survival.

Professor Alcock said: "There are already a large number of species that are endangered, because the forest itself is endangered.

Estimates 'exaggerated'

"We might be able to keep a few animals at the zoos, but we'd surely lose a lot of amphibians, reptiles and insects."

However, Philip Stott, professor of biogeography at the University of London, UK, told BBC News Online: "This model sounds to me to be highly simplistic in political, economic and ecological terms.

"Many scientists believe that deforestation estimates are greatly exaggerated, and that in the Amazon 87% may still be intact - perhaps more.

"There's always a lot of secondary regeneration, and you'd have to take that into account in any modelling."