The Independent/UK, October 21, 2005
Title: “Revealed: the True Devastation of the Rainforest
Author: Steve Connor
Faculty Evaluator: Myrna Goodman
Student Researcher: Courtney Wilcox and Deanna Haddock
New developments in satellite imaging technology reveal that the Amazon rainforest is being destroyed twice as quickly as previously estimated due to the surreptitious practice of selective logging.
A survey published in the October 21 issue of the journal Science is based on images made possible by a new, ultra-high-resolution satellite-imaging technique developed by scientists affiliated with the Carnegie Institution and Stanford University.
“With this new technology, we are able to detect openings in the forest canopy down to just one or two individual trees,” says Carnegie scientist Gregory Asner, lead author of the Science study and assistant professor of Geological and Environmental Sciences at Stanford University. “People have been monitoring large-scale deforestation in the Amazon with satellites for more than two decades, but selective logging has been mostly invisible until now.” While clear-cuts and burn-offs are readily detectable by conventional satellite analysis, selective logging is masked by the Amazon’s extremely dense forest canopy.
Stanford University’s website reports that by late 2004, the Carnegie research team had refined its imaging technique into a sophisticated remote-sensing technology called the Carnegie Landsat Analysis System (CLAS), which processes data from three NASA satellites—Landsat 7, Terra and Earth Observing 1—through a powerful supercomputer equipped with new pattern-recognition approaches designed by Asner and his staff.1
“Each pixel of information obtained by the satellites contains detailed spectral data about the forest,” Asner explains. “For example, the signals tell us how much green vegetation is in the canopy, how much dead material is on the forest floor and how much bare soil there is.”
For the Science study, the researchers conducted their first basin-wide analysis of the Amazon from 1999 to 2002. The results of the four-year survey revealed a problem that is widespread and vastly underestimated, “We found much more selective logging than we or anyone else had expected—between 4,600 and 8,000 square miles every year of forest spread across five Brazilian states,” Asner said.
Selective logging—the practice of removing one or two trees and leaving the rest intact— is often considered a sustainable alternative to clear-cutting. Left unregulated, however, the practice has proven to be extremely destructive.
A large mahogany tree can fetch hundreds of dollars at the sawmill, making it a tempting target in a country where one in five lives in poverty. “People go in and remove just the merchantable species from the forest,” Asner says. “Mahogany is the one everybody knows about, but in the Amazon, there are at least thirty-five marketable hardwood species, and the damage that occurs from taking out just a few trees at a time is enormous. On average, for every tree removed, up to thirty more can be severely damaged by the timber harvesting operation itself. That’s because when trees are cut down, the vines that connect them pull down the neighboring trees.
“Logged forests are areas of extraordinary damage. A tree crown can be twenty-five meters. When you knock down a tree it causes a lot of damage in the understory.” Light penetrates to the understory and dries out the forest floor, making it much more susceptible to burning. “That’s probably the biggest environmental concern,” Asner explains. “But selective logging also involves the use of tractors and skidders that rip up the soil and the forest floor. Loggers also build makeshift dirt roads to get in, and study after study has shown that those frontier roads become larger and larger as more people move in, and that feeds the deforestation process. Think of logging as the first land-use change.”
Another serious environmental concern is that while an estimated 400 million tons of carbon enter the atmosphere every year as a result of traditional deforestation in the Amazon, Asner and his colleagues estimate that an additional 100 million tons is produced by selective logging. “That means up to 25 percent more greenhouse gas is entering the atmosphere than was previously assumed,” Asner explains, a finding that could alter climate change forecasts on a global scale.
1. Mark Shwartz, “Selective logging causes widespread destruction, study finds,” Stanford University website, October 21, 2005.