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Satellite images reveal Amazon forest shrinking faster

New methods detect twice as much logging as previously estimated

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Brazil's Amazon rain forest - one of the most biologically productive regions on the planet - is disappearing twice as fast as scientists previously estimated.

That is the stark conclusion ecologist Gregory Asner and his colleagues reached after developing a new way to analyze satellite images to track logging there.

The team traces the additional loss to selective logging, which some environmental groups say is ocurring illegally. The technique removes trees piecemeal from a forest, rather than carving large swaths. This has made it easier to hide. This project is the first time satellites have been used to track selective logging. [Editor's note: The original version identified selective logging as illegal. Not all groups agree that the practice always occurs illegally.]

For the region, this activity increases the forest's vulnerability to wildfires and undermines its biological productivity. Selective logging in the region releases nearly 100 million tons of additional carbon dioxide into the atmosphere each year.

Ecologists and Brazilian officials long have known that selective logging occurs, says Dr. Asner, a researcher at the Carnegie Institution's Department of Global Ecology, based at Stanford University in Palo Alto, Calif. But gauging its extent by looking at changes in forest cover has been difficult. Sawmill surveys can yield results that either are incomplete or unreliable. Previous methods for analyzing Landsat satellite images couldn't render such tiny details.

Asner and his colleagues suspected their more tightly focused view would bring bad news. But the extent of the damage still surprised them. As the team huddled around a supercomputer terminal watching the first numbers emerge, "They were more than double what I expected," Asner recalls. "It's exciting science, but sobering."

For Daniel Nepstad, an ecologist at the Woods Hole Research Center an environmental policy and research organization in Woods Hole, Mass., the study "puts to rest a long-standing debate about how extensive selective logging is in the Amazon."

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