From: www.dailyclimate.org/
Published January 23, 2009 08:01 AM
Climate change has doubled forest mortality
The death rate of the most stable and resilient forests in western North
America has doubled during the past few decades as the climate has warmed,
according to research to be published Friday.
The increased mortality suggests future landscapes will be thinner, sparser
and far more susceptible to widespread diebacks.
The new data from a team of 11 scientists provide more evidence that climate
change is having a broad and significant impact, independent of other human
activities such as logging and development.
And while the study focused on Western North America, scientists say the
global temperature rise is likely affecting all the world’s forests — from
the Northern boreal to the Eastern hardwoods to the tropics — to some
degree.
In North America, scientists say, the trend is clear: Western forests are
becoming more susceptible to wildfire, disease and invaders such as bark
beetles. Average tree size is shrinking; creatures dependent on large,
old-growth trees will increasingly find themselves out of a home.
And as temperature and mortality climb, these forests will store less and
less carbon — and could potentially flip from being carbon sinks to carbon
sources, further speeding global warming.
"The important message here is that wherever we looked, mortality rates are
increasing," said Nathan Stephenson, a scientist with the U.S. Geological
Survey’s Western Ecological Research Center in California and a co-author on
the study, published in the journalScience.
"It’s very likely that mortality rates will continue to rise."
The research tracked growth rates and tree mortality from 1955 to the
present in 76 plots of old-growth forest across the West.
Tree death increased in every plot and every region, at every elevation, in
trees of every size and every type, scientists said. And the change is
happening fast, with estimated doubling periods ranging from 17 years in the
Pacific Northwest to 29 years in the Rocky Mountains. The birth rate for new
trees remained unchanged.
Temperature alone is driving this decline, researchers found. From the 1970s
to 2006, temperatures increased 0.3ºC to 0.4ºC per decade across the region,
drying out the snowpack, triggering an earlier spring melt and lengthening
the summer dry season.
"We do see clear evidence that climate change is resulting in an increase in
stand replacement," said Jerry Franklin, a professor of forest resources at
the University of Washington and another co-author. "These are what we
consider to be our most stable, most resilient stands."
The study's scale allowed researchers to discount other factors: Spreading
disease has increasingly afflicted vast swathes of North America’s pine and
fir forests, but when scientists excluded afflicted patches, the remaining
healthy stands saw the same increasing mortality rates.
Similarly, another blight for forest health, smog, could be discounted after
researchers found the death rate for trees growing in the relatively pure
air of Washington's Olympic Peninsula no different from those of trees
growing in California's smog-afflicted Sierra Nevada.
The findings, researchers said, have broad implications for land managers
and policy makers. For starters, Franklin said, it underscores the need to
preserve the remaining stands of old growth forests throughout the West.
Old growth stands are "extraordinary carbon stores," Franklin said,
sequestering a large mass of carbon in very stable conditions.
Greenhouse gas emissions associated with logging old growth - to say nothing
of habitat loss - cannot be mitigated by new growth, Franklin said.
"One lesson in it for me is ... we probably do not want to get into these
forests and mess around. Because we aren’t going to help. If anything, we
could potentially mess it up," he said.
New regulations will likely be needed, to both help the forest and keep
people safe, particularly as fire risk rises, said Thomas Veblen, a
professor of geography at the University of Colorado and another co-author.
"This is further evidence that we're really seeing continental-scale effects
of the warming," he said. "We have to start thinking outside the box in
terms of how as a society we adapt to the change that's under way."
Land managers say they are getting that message.
In California the Nature Conservancy is calling for the establishment of
large protected areas that permit species migration, promoting more
resilient ecosystems and sponsoring legislation in Sacramento requiring
wildlife corridors as condition for highway development, said Louis
Blumberg, director of the organization's California climate change team.
"And we're doing science," he said. "We're trying to figure it out, too."
But it is likely this latest data, from one of the largest-ever surveys of
North American forests, underestimates the true impact of climate change on
forest health.
The researchers did not include any Western forest stands hit by massive
trauma that is at least partially linked to climate, such as wildfires or
the bark beetle epidemic.
British Columbia has lost 40 million acres of forest to the bark beetle;
Colorado is approaching 2 million acres of dead forest; Wyoming just
recently crested the 1-million-acre mark, said Mary Ann Chambers,
spokeswoman for the U.S. Forest Service's Bark Beetle Incident Management
Team for the Rocky Mountain region.
Last summer the Forest Service closed a quarter of its 120 campgrounds to
remove dead trees, and more are dying: The beetle epidemic has recently
crested the continental divide, jumping from the predominantly lodgepole
pine forest on the Western Slope to a forest of mixed conifers to the east.
"The research says if the beetle is in lodgepole, it pretty much stays in
lodgepole," Chambers said. "But that isn't the case any more."
All this has an impact, said Kyle Patterson, a spokeswoman for the Rocky
Mountain National Park, where a popular camping spot will be closed this
spring so crews can essentially clear cut the dead trees.
"We held on for as long as we could," Patterson said. "There are a lot of
people who have been going to that campground for years. They saw the
(hills) getting redder and redder. They knew it was coming. It’s still very
hard to take."
"The forest is changing," she added. "It's very upsetting to those of us who
won't see it regenerate in our lifetimes."
2007. Copyright Environmental News Network To
subscribe or visit go to: http://www.enn.com
|