Fragmented rainforests can keep losing biodiversity for a century, according to new research in the October issue of Conservation Biology. While the bad news is that many more species are likely to go extinct, the good news is that we can save them if we act now.
"There is no room for complacency," says Thomas Brooks of the University of Arkansas in Fayetteville, who did the study with Stuart Pimm of Columbia University in New York City and Joseph Oyugi of the National Museums of Kenya in Nairobi.
Brooks and his colleagues studied the extinction of bird species in five fragments of Kakamega Forest, Kenya's only rainforest. The researchers determined the rate of bird extinction based in part on how long the fragment has been isolated and on the number of bird extinctions during that time. To check their method, they showed that it accurately accounts for the number of species that have been lost in eastern North America, where deforestation peaked 150 years ago.
Brooks and his colleagues found that within 50 years of isolation, 2,500-acre fragments of Kakamega Forest lose half the bird species likely to go extinct. They concluded that it will take about a century for fragmented tropical rainforests to lose all the bird species that will ultimately die out.
"Our results provide both encouragement and warning," say Brooks and his colleagues.
The warning is that without action, half of the world's 360 threatened forest bird species will be extinct in about 50 years. The encouraging conclusion is that because the most-recently isolated fragments probably still have most of their species, conserving these fragments will mean saving the greatest number of species.