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By Les Blumenthal, McClatchy Newspapers Les Blumenthal, Mcclatchy Newspapers
Sun Aug 29, 11:01 am ET
WASHINGTON A new study using laser pulses shot from satellites has found that
the world's tallest forests are those along the Pacific Northwest coast.
Though the findings shouldn't shock anyone who grew up in the region, they
offer another indication of how important these ancient trees eventually could
become.
The temperate forests of Douglas fir, Western hemlock, redwoods and sequoias
that stretch from northern California into British Columbia easily reach an
average height of more than 131 feet. That's taller than the boreal forests of
northern Canada and Eurasia, tropical rainforests and the broadleaf forests
common in much of the United States and Europe . The only forests that come
close are in Southeast Asia , along the southern rim of the Himalayas and in
Indonesia , Malaysia and Laos .
As scientists try to unravel the mystery of missing carbon, increasing
attention is focused on these forests.
From 15 percent to 30 percent of the 7 billion tons of carbon that are released
globally every year is unaccounted for, government scientists say. About 3
billions tons remain in the atmosphere, and the oceans absorb 2 billion tons.
Vegetation, including the forests, probably absorbs the remaining 1 billion to
2 billion tons, but no one knows for sure how much and where.
Scientists suspect that the forests with the biggest trees store the most
carbon, and the Northwest forests are probably among the largest carbon sinks
in the world. However, they also say that while slower-growing older trees
store more carbon, younger trees also absorb more carbon as they grow rapidly.
That sets up a debate about how forests should be managed, particularly whether
older trees should be cut to make way for younger ones or whether they should
be protected to store the carbon they contain.
"It's a hot topic," said Elaine Oneil , a research scientist at the University
of Washington's School of Forest Resources and the executive director of a
consortium that's been studying the issue. "We can't afford a one-size-fits-all
solution. We can't lock it all up, and it's not feasible to cut it all for
two-by-fours."
Ongoing studies using the satellites and lasers may provide valuable
information on how fast the forests are growing and how much carbon they store.
"All of the remote sensing is providing us with the ability to monitor changes
in the environment in a way you might not see on the ground," said Michael
Lefsky , an assistant professor in the department of forest, rangeland and
watershed stewardship at Colorado State University . "We are expecting under
global warming that the productivity of the forests will change."
Lefsky used data from a laser technology called LIDAR that's capable of
"capturing vertical slices" of surface features on Earth from satellites. It's
the same technology that geologists are using to map earthquake faults in
western Washington state .
With the help of computers, Lefsky put together a global forest height map
based on data from 250 million laser pulses collected during a seven-year
period.
LIDAR measures the height of forest canopies by shooting laser pulses and
measuring how much longer it takes for them to bounce back from the surface
than from the top of the forest canopy. The pulses can penetrate through the
canopy to the ground.
"It's like an echo," said Lefsky, whose findings were published in the journal
Geophysical Research Letters.
Overall, LIDAR offered direct measurements of only 2.4 percent of the Earth's
forested surfaces.
"This is really just a first draft and it will certainly be refined in the
future," he said.
Lefsky, who previously had done forest research at Oregon State University ,
said he wasn't surprised that the temperate conifer forests of the Northwest
coast had the tallest canopies. While the Northwest forests include the world's
tallest trees redwoods and sequoias they represent only a small fraction of
the region's timberlands, he said, but there are thousands of acres of other
tall trees.
In contrast to the Northwest stands, the boreal forests of mostly spruce, fir,
pine and larch have canopies that are typically less than 66 feet tall.
Relatively undisturbed tropical rain forests have canopies of 82 feet, and the
broadleaf forests of oak, beech and birch in much of the U.S. and Europe have
roughly the same canopy height.
Trees absorb carbon dioxide, a greenhouse gas, and convert it using water into
sugar and oxygen. Much of the sugar becomes cellulose, the key ingredient in
wood. From 45 percent to 50 percent of a tree's wood is carbon-based.
The trees and soil in national forests in Washington state , Oregon and
southeast Alaska store 10.8 billion tons of carbon, according to a Wilderness
Society analysis of U.S. Forest Service data earlier this year.
The analysis also found that of the 120 national forests, the 10 with the
highest carbon density were in Washington , Oregon and southeast Alaska .
Oneil's group, the Consortium for Research on Renewable Industrial Materials,
suggests that rather than leaving all the tall trees in place, where they could
be susceptible to bugs and fires, they be cut and used for wood products such
as building materials.
The carbon in those wood products would be stored permanently and their use
would reduce the need to manufacture cement and steel, a process that produces
greenhouse gases. In addition, the leftovers from milling the logs, such as
chips and sawdust, can be used for everything from bark mulch to biofuel for
power plants.
Carbon absorption by trees in the Northwest slows when they reach 30 to 70
years of age, Oneil said. By no means, Oneil said, is her group arguing that
all the old-growth forests in the Northwest be cut. The stands have other
important uses, such as providing habitat for wildlife and recreational
opportunities, she said. However, she suggested that the forests, particularly
on private lands, could be managed to absorb even more carbon.
"If you don't pick the carrots, you can't plant the next crop," she said.
Environmentalists said cutting the tall forests wasn't the answer, because that
could release up to 60 percent of the carbon that was stored in trees and the
soil.
"We need to preserve the old growth for existing (carbon) storage," said Mike
Anderson , a senior resource analyst with The Wilderness Society in Seattle .
Anderson didn't rule out using private lands to increase carbon storage.