Amazon Logging Twice as Heavy as Thought, Images Show

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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."

Illegal Logging

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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