Hidden Threats Take Toll in Amazon.

Studies of deforestation in the Brazilian Amazon have overlooked more than half of the actual rainforest damage occurring each year, reports a team of U.S. and Brazilian researchers.

Past assessments of the Amazon have used satellite images to tally deforested areas, where farmers and ranchers have clear-cut and burned all trees. Such work has not addressed logging, which removes only selected trees, or surface fires that burn down individual trees but do not denude the forest.

The new analysis, published in the April 8 NATURE, indicates that logging and these fires degrade a larger area of forest than does strict deforestation--especially in dry years.

"This will really change quite fundamentally the way we think about deforestation," says study leader Daniel C. Nepstad of the Woods Hole (Mass.) Research Center and the Amazon Institute for Environmental Research in Belem, Brazil. "It shows that the effects of people on forests can be much greater than we thought."

Other researchers question the exact numbers in the study but agree with the conclusion. "Our surveys do not consider impoverishment of the forest by logging," says Diogenes S. Alves of Brazil's National Institute for Space Research in Sao Jose dos Campos. "This is a serious issue."

Satellite surveys have difficulty picking out effects of logging and fires because they remain obvious only for a year, then new growth obscures the damage, says Nepstad. To estimate the impact of logging, he and his colleagues interviewed 1,393 managers of sawmills and obtained records of wood harvests for 1996 and 1997.

The team tested the accuracy of the sawmill data by measuring wood harvesting at 22 square-kilometer patches of forest. "What the loggers were telling us was right on the money," says Nepstad.

To estimate the effects of recent fires, the researchers interviewed 202 landholders whose properties total 9,200 [km.sup.2]. They checked this information against satellite data, which showed that the owners correctly gauged the number of fires but underestimated the area of burning by 43 percent.

Nepstad and his coworkers calculate that logging damaged 10,000 to 15,000 [km.sup.2] of undisturbed forest each year in 1996 and 1997. This represents 50 to 90 percent as much land as that totally deforested during 1996. The fire estimates are less precise but suggest that fires harmed an area roughly equal to the area of deforestation.

Logging and fire injuries can have far-reaching effects. By taking down trees, logging and fires open up the canopy, dry the forest floor, and increase the risk of fire. On a global scale, such forest degradation releases large amounts of carbon dioxide that are not currently included in global computations.

The combined effect of logging and fires is "a potentially large and significant phenomenon," says David Skole, a geographer at Michigan State University in East Lansing who uses satellite data to track deforestation. The new study, however, "doesn't provide us with direct measurements of the magnitude of this effect," he adds.

"It's very important to identify the size of the problem," says Eduardo Martins, president of the Brazilian Environment Institute in Brasilia. Logging is often the first step toward total deforestation, he says.