"Studies by the blue-chip Woods Hole Research Centre, carried out in
Amazonia, have concluded that the forest cannot withstand more than two
consecutive years of drought without breaking down.
Scientists say that this would spread drought into the northern
hemisphere and could massively accelerate global warming with
incalculable consequences.
The research - carried out by the Massachusetts-based centre in Santarem
on the Amazon River - has taken even the scientists conducting it by
surprise.
When Dr Dan Nepstead started the experiment in 2002 - by covering a
chunk of rainforest the size of a football pitch with plastic panels to
see how it would cope without rain - he surrounded it with sophisticated
sensors, expecting to record only minor changes.
The trees managed the first year of drought without difficulty. In the
second year, they sunk their roots deeper to find moisture, but
survived. But in year three, they started dying. Beginning with the
tallest the trees started to come crashing down, exposing the forest
floor to the drying sun.
By the end of the year the trees had released more than two-thirds of
the carbon dioxide they have stored during their lives, helping to act
as a break on global warming. Instead they began accelerating the
climate change.
The Amazon now appears to be entering its second successive year of
drought, raising the possibility it could start dying next year. The
immense forest contains 90 billion tons of carbon, enough in itself to
increase the rate of global warming by 50 per cent.
Nepstead expects "mega-fires" rapidly to sweep across the drying jungle.
With the trees gone, the soil will bake in the sun and the rainforest
could become desert.
Deborah Clark from the University of Missouri, one of the world's top
forest ecologists, says research shows "the lock has broken" on the
Amazon ecosystem and the Amazon is "headed in a terrible direction".