Human activities are degrading the Amazonian forest at twice the rate previously estimated, suggests a new study that adds the effects of logging to those of clear-cutting. The research appears in the 21 October issue of the journal Science, published by AAAS, the nonprofit science society.

Until now, satellite-based methods for measuring deforestation across large areas have only been capable of detecting clear-cut swaths of land, where all the trees are removed to clear space for farming or grazing.

A new satellite imaging method, developed by Gregory Asner of the Carnegie Institution of Washington and colleagues, detects deforestation on a finer scale, allowing researchers to identify areas where trees have been thinned, due mostly to "selective logging." In this type of deforestation, only certain marketable tree species are cut and logs are transported offsite to saw-mills. Little has been known about the extent or impacts of selective logging in Amazonia until now, according to the authors.

To detect and quantify the amount of selective logging in the five major timber production states of the Brazilian Amazon, the researchers used the new Carnegie Landsat Analysis System. This technology allowed them to delve into each pixel of the image produced by a trio of satellites and determine the percentage of forested and deforested land within each pixel. (In contrast, the conventional interpretation of a satellite image would consider each pixel as entirely forested or deforested.)

"This method gives us an incredible map of the ubiquitous but very diffuse types of disturbances that exist in Brazil or in any tropical forest," Asner said.

The researchers found that, from 1999 to 2002, selective l
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Contact: Natasha Pinol
npinol@aaas.org
+1-202-326-7088
American Association for the Advancement of Science
20-Oct-2005