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Logging Doubles Threat to Amazon
Satellite image of South America, with red areas showing selective logging in the Brazilian Amazon. The newly detected logging was achieved using the Carnegie Landsat Analysis System. Image courtesy of the Carnegie Institution of Washington/NASA.
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Human activities are degrading the Amazonian forest at twice the rate previously estimated, suggests a new study, published in the 21 October 2005 issue of the journal Science, that adds the effects of logging to those of clear-cutting.
Until now, satellite-based methods for measuring deforestation across wide areas have only been capable of detecting clear-cut swaths of land, where all the trees are removed to clear the land for farming or grazing. A new satellite imaging method, developed by Gregory Asner and colleagues, detects deforestation on a finer scale, allowing researchers to identify areas where trees have been thinned due to "selective logging." In this type of deforestation, only certain marketable tree species are cut and logs are transported off-site to saw-mills.
Little has been known about the extent or impacts of selective logging in Amazonia until now, according to the authors. Using a method that allowed them to determine the percentage of degradation within each pixel of a satellite image, the authors found that, from 1999 to 2002, selective logging added 60 to 128 percent more damaged forest area than was reported for deforestation alone in the same study period.
The total volume of harvested trees represents roughly 10 to 15 million metric tons of carbon removed from the ecosystem, according to the authors. They estimate that this amount represents 25 percent increase in the overall flow of carbon from the Amazonian forest to the atmosphere.
Kathy Wren
21 October 2005
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