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Will Forests Adapt to a Warmer World? |
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By Stephen Leahy - IPS/IFEJ*
Some
scientists believe that a warmer planet means forests will grow
more quickly. But others say forested areas will dry up or become
disease ridden.
TORONTO, Nov 20 (IPS/IFEJ) - Deforestation
remains the greatest current threat to the world's forests, claiming
10 to 15 million hectares of tree-covered areas every year, but
climate change may represent a bigger challenge in the long term,
scientists say.
"We're like a two-year-old playing with fire... We're messing around
with something dangerous and don't really understand what will happen,"
says William Laurance, of the Smithsonian Tropical Research Institute
in Balboa, Panama, in reference to climate change and the Amazon
rainforest.
Forests and other forms of life are now living on an "alien" planet
where the levels of carbon dioxide and other greenhouse gases in
the atmosphere are higher than they have been for a million years.
These unprecedented levels of greenhouse gases are creating a new,
hotter planet with weather that is much more extreme than in the
past.
What does this mean for the 20 percent of the Earth's original forests
that are still standing? Some scientists believe forests will grow
faster in a warmer world. Others say they are more likely to burn,
or suffer from disease or die from drought.
Laurance and his colleagues have shown that the higher levels of
carbon dioxide in the atmosphere are changing the very nature of
the existing forest in the Amazon.
"Trees in the rainforest are growing faster and dying faster, and
changing in species composition," he said, adding that the long-term
implications of these changes are not known.
Researchers predict that the Amazon region will become hotter and
drier, much like last year's record drought where Amazonian rivers
dried up and wildfires burned large areas of the surprisingly dry
forest.
Rainforests are very vulnerable to consecutive years of drought,
warned the U.S.-based Woods Hole Research Center recently. The Amazon
cannot withstand more than two consecutive years of drought without
breaking down, reported Woods Hole researchers in Santarem, a city
on the Amazon River in Brazil.
One of the reasons for this is that rainforests are rain-making
machines. About half of all the rainfall in the Amazon is almost
immediately returned to the atmosphere as water vapor via plant
respiration. That helps to maintain cloud cover and produce frequent
rainfall, especially in the dry season when forests are most vulnerable
to droughts and fires, says Laurance.
If the forests dry out too much, they cannot put water vapor into
the air, creating a cycle of less and less precipitation.
"In the Amazon, some models suggest that the system could destabilise
once more than 30 percent of the forest is lost," said Laurance,
acknowledging that this idea is conjecture.
Brazilian scientist and climate expert Carlos Nobre, of the National
Institute of Space Research (INPE), has said that 40 percent is
the tipping point where the world's greatest forest will irreversibly
turn into savanna. About 17 percent of the Amazon is already gone.
Although much smaller in area, the cloud forests of the Andes mountains
contain nearly twice as many plant species and four times as many
endemic plants as other parts of the world. Conditions there are
harsh, with cool to cold temperatures and poor soils, so plants
grow slowly. Scientists believe that most plants there will not
be able to survive the rising temperatures already underway -- which
may climb five degrees Celsius by 2100.
"Trees and plants can't move up mountains very far because of the
increasingly poorer soils," says Andreas Hamann, a forestry expert
at the University of Alberta, Canada.
Species migration for trees can be as slow as a few meters per century,
but temperature hikes in North America would require a northwards
shift of a 150 km to 550 km for many existing forest ecosystems
by 2100.
Rapidly changing temperatures are pushing forest ecosystems out
of equilibrium, says Hamann, who recently completed studies on the
impacts of climate change on Canadian forests. "It could take 2000
years to re-balance once temperatures stop climbing."
However, "it's not the temperature rise that is the big problem
for forests in the short term, it is the changes that come with
higher temperatures," Hamann explains.
Higher temperatures are changing weather patterns and producing
more extremes, including longer droughts and huge forest fires.
In 2003 alone, Siberia lost 40,000 square kilometers of boreal forest
to fires. Alaska and Canada experienced their worst fire year ever
in 2004.
Canadian Forest Service researchers say 2.6 million hectares are
being lost to fire every year, a huge increase from the more than
one million hectares lost in the early 1970s. They have predicted
that climate change will create still drier conditions in Canada's
and Russia's boreal forests, making future increases in fires a
virtual certainty.
Nadezhda Tchebakova, of the Russian Academy of Sciences Forest Research
Institute, goes further, predicting that the boreal forests will
become so dry by 2090 they will turn into steppe, or grassland.
But climate change will not be the end of forests.
Reforestation and natural regeneration have dramatically increased
the amount of forest in at least 22 countries, according to the
report published Nov. 13 by the Proceedings of the National Academy
of Sciences. China and India, for example, have more forest cover
than they did 15 years ago. Much of the U.S. northeast is nearly
all forest now, when 50 to 100 years it was farmland.
"Demand for paper and wood products are down and there is an increased
interest in reforestation," says study co-author Jesse Ausubel,
of Rockefeller University in New York. These new forests do not
have the biodiversity of original, old-growth forests, but they
"offer the chance for biodiversity to return".
* This story is part of a series of features
on sustainable development by IPS (Inter Press Service) and IFEJ
(International Federation of Environmental Journalists). |
