Careful analysis of satellite images indicates that the Amazon rain forest is being deforested at a considerably lower rate than recently estimated, but the impact on biological diversity may be greater than feared, University of New Hampshire and NASA scientists report.
That apparent paradox is because of the pattern of forest loss, the scientists report today in the journal Science. Forests in the Amazon region of Brazil are felled in irregular patches that create islands of trees too small to support plants and animals normally found there.
Besides stripping trees from 5,800 square miles of forest annually, an area the size of Los Angeles and Ventura counties combined, logging often fragments habitats and upsets the balance of predator and prey. It also exposes the edges of these forest islands to climate changes, foraging livestock, people and other influences that can harm sensitive plant and animal species.
This so-called edge effect, which the scientists blame for most of the damage in the Amazon, also has been seen near clear-cut logging operations in the Pacific Northwest. But the potential for damage in Amazonia is far higher because those rain forests pack half or more of all plant and animal species onto about 7% of the Earth's landmass.
"Implications for biological diversity are not encouraging and provide added impetus for the minimization of tropical deforestation," wrote the researchers, David Skole of the University of New Hampshire and Compton Tucker of the National Aeronautic and Space Administration's Goddard Space Flight Center in Maryland.
Tucker said he arrived at the glum assessment by combining this new deforestation map with earlier studies about how disturbed habitats affect the diversity of plant and animal species.
"I want to stress that we've only estimated what it is," he said. Field research is required to get a better sense of the problem, he added.
The news may be better when it comes to global warming, Skole said in a telephone interview from Paris, where he is conducting research. Rain forests often are burned or left to rot once they are felled, releasing carbon dioxide. Carbon dioxide and other gases are believed to trap heat close to Earth's surface in a hypothetical thermal buildup called the greenhouse effect.
"There is almost a straight-line relationship between deforestation and carbon dioxide," Skole said. "If deforestation declines, that much less carbon dioxide is released."
