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Deforestation Worse Than Thought in Brazil, Scientists Say

Posted on: Thursday, 20 October 2005, 15:00 CDT

Until recently, scientists studying the degradation of the Amazon's forests haven't been able to see all the damage for the trees. With a computer-aided look, researchers reported Friday that twice as much of the basin has been disturbed by tree-cutting than previously thought.

Satellite-imaging to measure deforestation has been capable of detecting only clear-cut swaths of land, where all the trees have been removed or burned to allow farming or cattle grazing.

Now, a new satellite-imaging system developed by researchers at Carnegie Institution and Stanford University can spot the loss of forest canopy on a finer scale, allowing them to take into account areas where a few trees have been thinned.

"With this new technology, we are able to detect openings in the forest canopy down to just one or two individual trees,'' said Greg Asner, a Carnegie scientist and lead author of the report on selective logging published in the journal Science.

"Selective logging" _ the practice of cutting one or two high-value trees, like mahogany, in an area and leaving the rest intact _ has been considered by some a sustainable alternative to clear-cutting.

Brazil's Space Research Institute has used remote-sensing to measure deforestation for more than 20 years, but the resolution of the photos wasn't sharp enough to spot locations where only a few trees had been cut and hauled away to saw-mills.

Asner and colleagues developed a new computer-aided system to analyze the images and then worked with Brazilian scientists doing ground surveys for three years to confirm on the ground what was detected from space.

"With the new Carnegie system, we can now see what's happening from the top of the forest all the way to the soil; we have a whole new picture of the Amazon region and selective logging,'' said Jose Silva, a study co-author and researcher at the Brazilian Agricultural Research Corp.

The scientists found that selective logging leaves a much bigger footprint than had been thought, creating big gaps in the forest canopy that disrupt the local environment. In addition, the scientists saw large amounts of brush from limbs trimmed from the trees and other vegetation trimmed to haul the logs away.

"Logged forests are areas of extraordinary damage,'' Asner said. "A tree crown can be 25 meters (82 feet) across. When you knock down a tree, it causes a lot of damage in the under story. It's a debris field down there."

Asner's team discovered that each year, "an area about the size of Connecticut is disturbed this way. Selective logging negatively impacts many plants and animals and increases erosion and fires. Additionally, up to 25 percent more carbon is released to the atmosphere each year, above that from clear-cutting, by decomposition of what the loggers leave behind."

Using supercomputers in the Carnegie Department of Global Ecology at Stanford, the researchers can analyze overnight spectral data showing what's green, what's brown and what's bare soil in each 98-by-98 foot pixel of a satellite image covering millions of square miles.

The scientists found that, from 1999 to 2002, selective logging added 60 percent to 128 percent more damaged forest area _ 4,685 to 7,973 square miles _ than was reported using standard satellite imaging.

Although selective logging is generally illegal in Brazil, the laws have been virtually impossible for authorities to enforce. The scientists found a number of national forests, parks and indigenous reserves had been hit by the illegal logging.

Asner hopes that eventually his team will be able to use the new system to give Brazilian authorities real-time notice of where illegal cutting is going on. "They can't have a cop on every corner, so our idea is to give them these results in hopes that it might help their law enforcement effort,'' he said.

On the Net: http://www.sciencemag.org

Globalecology.Stanford.edu

(Contact Lee Bowman at BowmanL(at)SHNS.com. Distributed by Scripps Howard News Service, http://www.shns.com)

© 2005 Scripps Howard News Service.

All Rights Reserved.

Source: Scripps Howard

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