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http://news.yahoo.com/s/csm/20051021/wl_csm/odeforest_1
Satellite images reveal Amazon forest shrinking faster
By Peter N. Spotts, Staff writer of The Christian
Science Monitor Fri Oct 21, 4:00 AM ET
Brazil's
Amazon rain forest - one of the most biologically
productive regions on the planet - is disappearing
twice as fast as scientists previously estimated.
That is the stark conclusion ecologist Gregory Asner
and his colleagues reached after developing a new way
to analyze satellite images to track logging there.
The team traces the additional loss to illegal
selective logging, which removes trees piecemeal from
a forest, rather than carving large swaths. This has
made it easier to hide. This project is the first time
satellites have been used to track selective logging.
For the region, this activity increases the forest's
vulnerability to wildfires and undermines its
biological productivity. Illegal selective logging in
the region releases nearly 100 million tons of
additional carbon dioxide into the atmosphere each
year.
Ecologists and Brazilian officials long have known
that illegal selective logging occurs, says Dr. Asner,
a researcher at the Carnegie Institution's Department
of Global Ecology, based at Stanford University in
Palo Alto, Calif. But gauging its extent by looking at
changes in forest cover has been difficult. Sawmill
surveys can yield results that either are incomplete
or unreliable. Previous methods for analyzing Landsat
satellite images couldn't render such tiny details.
Asner and his colleagues suspected their more tightly
focused view would bring bad news. But the extent of
the damage still surprised them. As the team huddled
around a supercomputer terminal watching the first
numbers emerge, "They were more than double what I
expected," Asner recalls. "It's exciting science, but
sobering."
For Daniel Nepstad, an ecologist at the Woods Hole
Research Center an environmental policy and research
organization in Woods Hole, Mass., the study "puts to
rest a long-standing debate about how extensive
selective logging is in the Amazon."
The results come from new supercomputer software the
team developed. Over several years, the research group
- which included scientists from Brazil - gradually
squeezed more detail out of satellite images.
Initially the team could detect changes to a patch of
forest roughly 14 miles on a side. That shrank to a
patch 98 feet on a side - small enough to spot the
holes selective logging leave in the forest canopy.
Asner's group fed Landsat images from 1999 to 2002
into the computer, which hunted for the telltale
holes.
The results boosted the estimates of deforestation
during the period from 60 to 123 percent, depending on
which of the five logging-intensive Brazilian states
they examined. The group verified the results with
field surveys. Their results appear in Friday's
edition of the journal Science.
Over the long term, Asner adds, he plans to use the
technique to look at other tropical rain forests, such
as those in Peru and Bolivia.
Deforestation can radically alter the environmental
"services" the forests provide - from scrubbing the
atmosphere of CO2 and harboring useful plants and
animals to reducing erosion.
For example, in a related Science research paper,
Columbia University ecologist Daniel Bunker and
colleagues found that above-ground carbon storage
varied widely, depending on which tree species vanish
from within a patch of tropical rain forest and what
triggered their loss.
In a 123-acre tropical-forest research site in Panama,
they experimented with different mixes of species. The
results show that carbon storage is strongly
influenced by the types of trees present and the ways
in which they are lost. Selective logging of prized
hardwoods removes a small number of species from a
forest. But it substantially reduces the forest's
above-ground carbon storage because the lost wood is
dense.
The bottom line, Dr. Bunker says, is that preserving
species diversity may be the best way to ensure humans
continue to reap the services healthy ecosystems
provide.
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