Amazon Logging Twice as Heavy as Thought, Images Show
for National Geographic News
|October 20, 2005|
Damage to the Amazon rain forest has been underestimated by half,
according to new high-resolution satellite images, which have revealed
long-hidden logging activities.
Scientists say a new satellite imaging system that can penetrate the rain forest canopy shows that "selective logging," the singling out and cutting of commercially prized trees, poses a far bigger threat to the Earth's largest tropical forest than previously thought.
Writing in tomorrow's issue of the journal Science, researchers warn that their study has far-reaching implications for rain forests worldwide.
Lead author Greg Asner, an ecologist at the Carnegie Institution's Department of Global Ecology in Palo Alto, California, says that for decades loggers have been targeting and extracting high-value trees one by one, with the rain forest canopy covering their tracks.
"We discovered that annually an area the size of Connecticut is disturbed this way," he said. "Timber harvests are much more widespread than previously thought."
Until now satellite-based forest monitoring was unable to penetrate the upper layers of forest leaves, only detecting swathes cleared either for farmland or by major logging operations.
The new technology, developed by Carnegie scientists, allowed researchers to pinpoint very small areas of deforestation using large-scale, high-resolution images.
The system was used to detect selective logging in the top five timber-producing states of the Brazilian Amazon between 1999 and 2002.
Affected areas ranged from 4,660 to 7,650 square miles (12,070 to 19,820 square kilometers) each year, where between 953 million and 1.8 billion cubic feet (27 and 50 million cubic meters) of timber was removed annually.
The authors say this represents a 60 to 123 percent increase on previously reported damage to the Amazon forest during the four-year study period.
"We expected to see large areas of logging. But the extent to which logging penetrates deep into the frontier is much more dramatic than we anticipated," said co-author Michael Keller of the U.S. Forest Service.
The authors say that little is known about the extent of selective logging in tropical forests in the Amazon or elsewhere. They note that it causes widespread damage to surrounding trees and other vegetation.
It can also lead to soil erosion, increased risk of forest fires, and higher impacts on threatened animal species.
"A tree crown can be 25 meters [82 feet wide]," Asner said. "When you knock down a tree it causes a lot of damage to the understory. It's a debris field down there."
Other scientists and conservation groups say the new satellite images confirm the potential threat of selective logging to rain forest ecosystems.
"This excellent study puts to rest a longstanding debate about how extensive selective logging is in the Amazon," said Daniel Nepstad, an ecologist at the Woods Hole Research Center in Massachusetts.
"The results are of great concern, since logging punches big holes in the dense forest canopy, increasing the likelihood of devastating forest fire."
Selective logging can benefit forest diversity if it is managed properly and sustainably, according to Beatrix Richards, senior forests officer for WWF, the global conservation organization.
But, she added, "if it's not managed properly it can dry out the rain forest by changing the physical condition of the forest completely."
The study team reports that it identified areas of illegal logging, including activity in several protected national reserves, parks, and indigenous lands.
"Much of the logging [in Brazil] is illegal but difficult to enforce, because it is usually clandestine," Asner said.
The researchers say the potentially harmful effects of such deforestation may be felt far beyond the Amazon region.
They calculate that the total volume of harvested trees during the study period amounts to 10 million to 15 million metric tons (11 to 17 million tons) of carbon, representing a 25 percent increase in the overall flow of carbon from the Amazon forest to the atmosphere in the form of CO2.
Carbon dioxide is a major greenhouse gas and a driver of global warming.
Tree stumps, dead foliage, and roots left behind to rot also return to the atmosphere as CO2, the researchers add.
The team hopes its new monitoring techniques can be expanded to other tropical forest regions, such as Central Africa and Southeast Asia.
WWF's Richards says such a system would provide "a better picture of what is happening in these areas."
"It is also a much safer alternative," she added. "There have been a number of people who have been injured, even killed, when trying to monitor logging on the ground."
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