for National Geographic News
Even limited logging in the Amazon rain forest often leads to entire swaths of forest being completely cleared, according to the first-ever broad-scale study of logging in the region.
No previous study has shown such a close relationship between selective logging, in which only a limited number of trees per acre are harvested, and deforestation that follows.
Gregory Asner of the Carnegie Institution's Department of Global Ecology in Stanford, California, led the research.
The team used new remote sensing techniques to monitor the effects of logging over 784,000 square miles (2 million square kilometers) of rain forest in northern Brazil.
(See Brazil map.)
The team monitored the region from 1999 to 2004. The results showed that nearly one-third of the areas that were logged selectively were completely deforested for grazing and other uses within four years.
Sixteen percent of selectively logged forests were cleared within just one year.
The scientists say the rain forests are made vulnerable to clear-cutting by the networks of access roads left behind by logging operations.
"When small roads are cut into the forest for logging, others follow and open up the forest even more," Asner said.
Commenting on the study, William Laurance of the Smithsonian Tropical Research Institute in Manaus, Brazil, said it "confirms what many of us have long suspectedthat logging is a key, if indirect, driver of Amazonian forest destruction."
The report appears in today's edition of the Proceedings of the National Academy of Sciences.
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