Selective Logging Not So Benign

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“This was totally surprising to us and alarming to our colleagues,
especially those interested in conservation, climate change and the
ability of governments like Brazil to enforce environmental laws,” he
notes.

“When a tree trunk is removed, the crown, wood debris and vines are
left behind to decompose, releasing carbon dioxide gas into the
atmosphere,” Asner says. “Sawmills often have an efficiency level of
about 30 to 40 percent, so large amounts of sawdust and scrap also
decompose into atmospheric CO2.”

An estimated 400 million tons of carbon enter the atmosphere every
year as a result of traditional deforestation in the Amazon, and
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.
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Phys0rg.com
Science Physics Tech Nano News
October 21, 2005

Selective Logging Causes Widespread Destruction Of Brazil’s Amazon: Study
http://www.physorg.com/news7448.html

Selective logging – the practice of removing one or two trees and
leaving the rest intact – is often considered a sustainable
alternative to clear-cutting, in which a large swath of forest is cut
down, leaving little behind except wood debris and a denuded
landscape.

But a new satellite survey of the Amazon Basin in Brazil reveals that
every year unregulated selective logging of mahogany and other
hardwoods destroys an area of pristine rainforest big enough to cover
the state of Connecticut.

The survey, published in the Oct. 21 issue of the journal Science,
was made possible because of 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, by courtesy, in the Stanford University
Department of Geological and Environmental Sciences.

“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.”

The Amazon Basin contains the largest contiguous rainforest on
Earth–a vast region nearly as big the continental United States that
includes portions of Brazil and seven other South American countries.

Conventional satellite surveys reveal that, in an average year, an
estimated 5,800 square miles of Amazon forest (roughly the size of
Connecticut) are burned or clear-cut to make way for cattle ranching,
farming and other development. But when selective logging is factored
in, that figure increases two-fold, Asner and his co-workers found.

“This was totally surprising to us and alarming to our colleagues,
especially those interested in conservation, climate change and the
ability of governments like Brazil to enforce environmental laws,” he
notes.

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 35 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 30 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.”

Previous studies have shown that in logged forests, 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 says.

“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.”

Logging also has a significant impact on the food web, Asner says,
noting that nearly a third of the planet’s land species inhabit the
Amazon rainforest–from insects to jaguars and everything in between.
“Studies constantly show declines in primate and other mammal
populations following selective logging, and rates of forest
re-growth indicate that full restoration of habitats are likely slow
for large predators,” the authors write.

Another concern is climate change. “When a tree trunk is removed, the
crown, wood debris and vines are left behind to decompose, releasing
carbon dioxide gas into the atmosphere,” Asner says. “Sawmills often
have an efficiency level of about 30 to 40 percent, so large amounts
of sawdust and scrap also decompose into atmospheric CO2.”

An estimated 400 million tons of carbon enter the atmosphere every
year as a result of traditional deforestation in the Amazon, and
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.

Cryptic deforestation

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. “We’ve been working for eight years to
develop analytical techniques that can detect this very cryptic form
of deforestation,” Asner says. “Using satellite data, we developed a
model that detects the physical changes to the forest. We started to
have success about three years ago at a scale of about 200 hundred
square miles. This was the first solid, quantitative detection of
logging-related damage to forest canopies.”

By late 2004, the research team had refined its 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.

“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. Extracting those data has been a Holy Grail of
remote sensing. With CLAS, we’ve been able to obtain a spatial
resolution of 98 feet by 98 feet for the Brazilian Amazon Basin.
That’s huge.”

CLAS technology

For the Science study, the researchers conducted their first
basin-wide analysis of the Amazon from 1999 to 2002. “With CLAS, data
analysis that used to take a year now can be done in hours,” Asner
says. “We can run the entire Amazon overnight. In fact, the 600
images produced for the study were analyzed by just three technicians
in my lab at the Carnegie Department of Global Ecology.”

The results of the four-year survey revealed a problem that is
widespread and vastly underestimated, according to Asner. “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,” he says.

To corroborate their findings, the researchers compared the satellite
observations against on-the-ground field measurements of canopy
damage following selective logging.

“We surveyed thousands of hectares of logged forest, mapping the
precise location of each felled tree, skid, log deck, etc.,” Asner
explains. “We then measured the canopy damage at each of the 11,000
GPS [Global Positioning System] points to compare the satellite-based
canopy damage to field-based canopy damage.”

The results of the comparative analysis “proved that traditional
analytical methods missed about 50 percent of the canopy damage
caused by timber harvesting operations,” Asner and his co-authors
wrote.

The Science study was conducted in close collaboration with the
Brazilian agricultural research agency , including co-author Jose N.
Silva. “The Brazilian government has laws against these logging
operations, but they can’t enforce them over the enormous geography
we’re talking about,” Asner says. “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.”

Other co-authors of the study are David Knapp, Eben Broadbent and
Paulo Oliveira of the Carnegie Institution’s Department of Global
Ecology at Stanford; and Michael Keller of the USDA Forest Service
and the University of New Hampshire. Research was supported by the
Carnegie Institution at Stanford and NASA.

Copyright 2005 by Space Daily, Distributed United Press International

This news is brought to you by PhysOrg.com
http://www.physorg.com/news7448.html

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