Amazon Rain Forest Not Helped by "Light" Logging

Scott Norris
for National Geographic News
August 1, 2006
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 suspected—that 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.

"Pandora's Box"

For the most part, logging and forest clearing in the Amazon are carried out by different groups for different purposes.

Selective tree harvesters have an interest in maintaining the forests. But ranchers and farmers carry out most of the Amazon's deforestation in their efforts to clear new areas for agricultural use.

The new study highlights how the two practices are linked by road building.

Within about three miles (five kilometers) of main roads, both logged and unlogged areas are highly vulnerable to deforestation, the research showed.

In a broader band, from 3.1 to 15.5 miles (5 to 25 kilometers) from main roads, logged areas are two to four times more likely than unlogged areas to be cleared within four years.

"Logging often opens up a Pandora's box of spontaneous forest colonization by slash-and-burn farmers, ranchers, hunters, miners, and land speculators," the Smithsonian's Laurance said.

Because of its destructive consequences, selective logging as it's currently practiced appears not to be effective in keeping rain forests intact, the scientists conclude.

"Selective logging has been heralded by the timber industry and conservation groups as a sustainable alternative to clear-cutting," Asner said.

"But if the recent past is any indication, logging has not been treated as a sustainable land use."

The researchers say sustainability depends on the type of logging being practiced.

One encouraging finding was that nearly one-fourth of logged areas showed only minimal damage.

Study co-author Michael Keller says these were likely regions harvested by small-scale operators specializing in particular tree species.

The report also backed other recent studies in showing that reserve areas appear to be highly effective in limiting both logging and deforestation.

(Read related news: "Indigenous Lands Help Protect Amazon Forests, Study Finds" (February 28, 2006).]

New Technology

The new study also showcases a powerful new method for measuring logging impacts and assessing the condition of tropical forests.

Scientists have long used satellite imagery to monitor deforestation, but damage caused by small-scale logging has been much harder to track from space.

Asner's group spent years developing the first remote monitoring system sensitive enough to detect small disturbances in the forest canopy—the overhead cover of leaves and branches—that signal selective logging.

The more refined system can not only identify where logging is occurring but also measure its impact on forest habitat.

In a written commentary that accompanies the study, Lisa Curran of the School of Forestry and Environmental Studies at Yale University calls the new remote sensing technique a "major breakthrough."

"The broad application [of the new remote sensing method] could potentially revolutionize monitoring of logging operations and improve land management," Curran writes.

The development comes at a critical time for Brazil, which recently enacted sweeping new legislation for Amazon forest management, including much tighter control of logging.

Brazil's National Space Research Institute is developing its own system for large-scale forest monitoring, using methods similar to those of Asner's group.

"I'm very hopeful," Asner said. "The new Brazilian logging regulations promise to radically change what we've observed in the recent past."

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