An international research team has discovered that forest fragmentation poses an even greater threat to Amazonian biodiversity than previously thought.

Their findings, to be published next week (27 November 1 December) in the journal Proceedings of the National Academy of Sciences USA, summarizes key findings from the worlds largest and longest-running experimental study of habitat fragmentation.

The Amazon contains the planets most biologically diverse tree communities, with up to three hundred species occurring in an area the size of just two football fields. These forests are being rapidly felled and fragmented for timber operations, cattle ranches and industrial soy farms.

The team, led by William Laurance of the Smithsonian Tropical Research Institute in Panama, has been studying the fates of nearly 32,000 Amazonian trees since 1980. The most striking finding, say the authors, is the remarkable speed at which tree communities are changing in forest fragments.

Rainforest trees can live for centuries, even millennia, said Laurance, so none of us expected things to change too fast. But in just two decadesa wink of time for a thousand year-old treethe ecosystem has been seriously degraded.

The main driver of these changes, say the authors, is ecological changes near the margins of forest fragments. When you fragment the rainforest, hot winds from the surrounding pastures blow into the forest and kill many trees, which just cant handle the stress, said Henrique Nascimento, a team member from Brazils National Institute for Amazonian Research in Manaus. Also, winds build up around the fragment and knock down a lot of trees.

The trees that regenerate in their place are very different from the trees that died. When you fragment a forest, the winners are common pioneer and generalist species that like forest disturbance, said Laurance. The losers are rare, slow-growing tree species that provi
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Contact: William Laurance
laurancew@si.edu
Smithsonian Tropical Research Institute
27-Nov-2006