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[pattrice jones]

"If you change the tree communities then other species - especially the 
animals that feed on and pollinate the trees - will undoubtedly change 
as well."

Greenhouse gases threaten tree species in remote parts of the Amazon
By Steve Connor Science Editor
The Independent (UK)
11 March 2004

Pristine parts of the Amazon rainforest that were thought to have 
escaped the effects of human encroachment have changed dramatically 
over the past 20 years, scientists have determined.

The delicate balance of tree species growing in some of the most remote 
regions of the Amazon has been altered significantly and the scientists 
believe it is a direct result of increases in carbon dioxide emissions 
caused by humans. Small, slower-growing trees that thrived beneath the 
forest canopy are losing out to faster-growing varieties because the 
Amazon is in effect being artificially "fertilised" with increased 
levels of carbon dioxide in the atmosphere.

The result is a change in the composition of the major groups of trees, 
which could have a long-term impact in the vital role played by the 
Amazon in soaking up excess carbon dioxide, the scientists said. 
Amazonian rainforests are renowned for their rich diversity of trees. 
But some areas appear to be doing better at the expense of others, as 
atmospheric levels of carbon dioxide continue to rise, said William 
Laurance of the Smithsonian Tropical Research Institute. For the past 
two decades, the scientists, whose study is published in the journal 
Nature, tracked the growth of nearly 14,000 trees in 18 plots of land 
which were scattered throughout 120 square miles.

Dr Laurance said the researchers deliberately chose the plots because 
they were remote and well away from any human activity, such as logging 
and deforestation, but the changes they saw were nevertheless dramatic. 
He added: "The changes in Amazonian forests really jump out at you. 
It's a little scary to realise that seemingly pristine forests can 
change so quickly and dramatically.

"Sadly, this could be a signal that the forest's ecology is changing in 
fundamental ways. Tropical rainforests are renowned for having lots of 
high specialised species. If you change the tree communities then other 
species - especially the animals that feed on and pollinate the trees - 
will undoubtedly change as well."

Alexandre Oliveira, of the University of Sao Paulo in Brazil, said that 
during the period of the study most trees grew faster, but at different 
rates, leading to a scenario of winners and losers.

Dr Oliveira said: "In general, large, fast-growing trees are winning at 
the expense of smaller trees that live in the forest understorey."

The scientists found that out of a total of 115 tree genera in the 
Amazon, 27 had changed significantly either by increasing or decreasing 
in growing density, a rate of change that is 14 times greater than 
expected if it was due to chance.

Henrique Nascimento, a Brazilian scientist with the Smithsonian 
Tropical Research Institute, said that the decline of smaller, 
shade-tolerant trees could have important implications for the overall 
health of the Amazon.

Dr Nascimento said: "The decline of many small trees is intriguing 
because they tend to be so specialised. They live in the dark interior 
of the forest and are the only trees that can flower and reproduce in 
the shade." One possible reason for the change is that rising levels of 
carbon dioxide - which have increased by 30 per cent in the past 200 
years - could be fertilising the trees and causing them to grow faster, 
especially the larger species with wood that is not as dense as the 
shade-loving varieties.

If this proves to be the case then the changes could have an important 
effect on the ability of the Amazon to act as a "sink" for atmospheric 
carbon, an impact that could exacerbate global warming.

Thomas Lovejoy of the Heinz Centre for Science, Economics and 
Environment in Washington, which helped to fund the study, said: "This 
appears to be another signal of effects on nature from increasing 
greenhouse gas concentrations and climate change. We need more research 
to see if these remarkable changes are also happening in other tropical 
forests."

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