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| Mountain Pine beetle damaged forest; pine needles turn red |
By Justin Gillis, The New York Times, October 1, 2011
WISE RIVER, Mont. —
The trees spanning many of the mountainsides of western Montana glow an earthy
red, like a broadleaf forest at the beginning of autumn.
But these trees are
not supposed to turn red. They are evergreens, falling victim to beetles that
used to be controlled in part by bitterly cold winters. As the climate warms,
scientists say, that control is no longer happening.
Across millions of acres, the pines of the northern and central
Rockies are dying, just one among many types of forests that are showing signs
of distress these days.
From the mountainous Southwest deep into Texas, wildfires raced across
parched landscapes this summer, burning millions more acres. In Colorado, at
least 15 percent of that state’s spectacular aspen forests have gone into
decline because of a lack of water.
The devastation extends worldwide. The great euphorbia trees of southern
Africa are succumbing to heat and water stress. So are the Atlas cedars of
northern Algeria. Fires fed by hot, dry weather are killing enormous stretches
of Siberian forest. Eucalyptus trees are succumbing on a large scale to a heat
blast in Australia, and the Amazon recently suffered two “once a century”
droughts just five years apart, killing many large trees.
Experts are scrambling to understand the situation, and to predict how
serious it may become.
Scientists say the future habitability of the Earth might well depend on the answer. For,
while a majority of the world’s people now live in cities, they depend more
than ever on forests, in a way that few of them understand.
Scientists have figured out — with the precise numbers deduced only
recently — that forests have been absorbing more than a quarter of the carbon
dioxide that people are putting into the air by burning fossil fuels and other
activities. It is an amount so large that trees are effectively absorbing the
emissions from all the world’s cars and trucks.
Without that disposal service, the level of carbon dioxide in the
atmosphere would be rising faster. The gas traps heat from the sun, and human
emissions are causing the planet to warm.
Yet the forests have only been able to restrain the increase, not halt
it. And some scientists are increasingly worried that as the warming
accelerates, trees themselves could become climate-change victims on a massive
scale.
“At the same time that we’re recognizing the potential great value of
trees and forests in helping us deal with the excess carbon we’re generating,
we’re starting to lose forests,” said Thomas W. Swetnam, an expert on forest history
at the University of Arizona.
While some of the forests that died recently are expected to grow
back, scientists say others are not, because of climate change.
If forests were to die on a sufficient scale, they would not only stop
absorbing carbon dioxide, they might also start to burn up or decay at such a
rate that they would spew huge amounts of the gas back into the air — as is
already happening in some regions. That, in turn, could speed the warming of
the planet, unlocking yet more carbon stored in once-cold places like the
Arctic.
Scientists are not sure how likely this feedback loop is, and they are
not eager to find out the hard way.
“It would be a very different world than the world we’re in,” said Christopher B. Field, an ecologist at the
Carnegie Institution for Science.
It is clear that the point of no return has not been reached yet — and
it may never be. Despite the troubles of recent years, forests continue to take
up a large amount of carbon, with some regions, including the Eastern United
States, being especially important as global carbon absorbers.
“I think we have a situation where both the ‘forces of growth’ and the
‘forces of death’ are strengthening, and have been for some time,” said Oliver
L. Phillips, a prominent tropical forest researcher with the
University of Leeds in England. “The latter are more eye-catching, but the
former have in fact been more important so far.”
Scientists acknowledge that their attempts to use computers to project
the future of forests are still crude. Some of those forecasts warn that climate
change could cause potentially widespread forest death in places like the
Amazon, while others show forests remaining robust carbon sponges throughout
the 21st century.
“We’re not completely blind, but we’re not in good shape,” said
William R. L. Anderegg, a researcher at Stanford University.
Many
scientists say that ensuring the health of the world’s forests requires slowing
human emissions of greenhouse gases. Most nations committed to doing so in a
global environmental treaty in 1992, yet two decades of negotiations have
yielded scant progress.
n the near term,
experts say, more modest steps could be taken to protect forests. One promising
plan calls for wealthy countries to pay those in the tropics to halt the
destruction of their immense forests for agriculture and logging.
But now even that plan is at risk, for lack of money. Other
strategies, like thinning overgrown forests in the American West to make them
more resistant to fire and insect damage, are also going begging in straitened
times. With growing economic problems and a Congress skeptical of both climate
science and new spending, chances for additional funding appear remote.
So, even as potential solutions to forest problems languish, signs of
trouble build.
In the 1990s, many of the white spruce trees of Alaska’s Kenai
Peninsula were wiped out by beetles. For more than a decade, other beetle
varieties have been destroying trees across millions of acres of western North
America. Red-hued mountainsides have become a familiar sight in a half-dozen
states, including Montana and Colorado, as well as British Columbia in Canada.
Researchers refer to events like these as forest die-offs, and they
have begun to document what appears to be a rising pattern of them around the
world. Only some have been directly linked to global warming by scientific
studies; many have yet to be analyzed in detail. Yet it is clear that hotter
weather, of the sort that science has long predicted as a consequence of human
activity, is playing a large role.
Many scientists had hoped that serious forest damage would not set in
before the middle of the 21st century, and that people would have time to get
emissions of heat-trapping gases under control before then. Some of them have
been shocked in recent years by what they are seeing.
“The amount of area burning now in Siberia is just startling —
individual years with 30 million acres burned,” Dr. Swetnam said, describing an
area the size of Pennsylvania. “The big fires that are occurring in the
American Southwest are extraordinary in terms of their severity, on time scales
of thousands of years. If we were to continue at this rate through the century,
you’re looking at the loss of at least half the forest landscape of the
Southwest.”
The Carbon Dioxide Mystery
In the 1950s, when a scientist named Charles David Keeling first obtained accurate
measurements of carbon dioxide in the atmosphere, a mystery presented itself.
Only about half the carbon that people were releasing into the sky seemed to be
staying there. It took scientists decades to figure out where the rest was
going. The most comprehensive estimates on the role of forests were published
only a few weeks ago by an international team of scientists.
As best researchers can tell, the oceans are taking up about a quarter
of the carbon emissions arising from human activities. That is causing the sea
to become more acidic and is expected to damage marine life over the long run,
perhaps catastrophically. But the chemistry is at least somewhat predictable,
and scientists are reasonably confident the oceans will continue absorbing
carbon for many decades.
Trees are taking up a similar amount of carbon, but whether this will
continue is much less certain, as the recent forest damage illustrates.
Carbon dioxide is an essential part of the cycle of life on Earth, but
geologic history suggests that too much can cause the climate to warm sharply.
With enough time, the chemical cycles operating on the planet have a tendency
to bury excess carbon.
In the 19th century, humans discovered the usefulness of some forms of
buried carbon — coal, oil and natural gas — as a source of energy,
and have been perturbing the natural order ever since. About 10 billion tons of
carbon are pouring into the atmosphere every year from the combustion of fossil
fuels and the destruction of forests.
The
concentration of the gas in the atmosphere has jumped 40 percent since the
Industrial Revolution, and scientists fear it could double or even triple this
century, with profound consequences.
While all types of
plants absorb carbon dioxide, known as CO2, most of them return it to the
atmosphere quickly because their vegetation decays, burns or is eaten. Every
year, during the Northern Hemisphere growing season, plants and other organisms
inhale some 120 billion tons of carbon from the atmosphere, then exhale nearly
the same amount as they decay in the winter.
It is mainly trees
that have the ability to lock carbon into long-term storage, and they do so by
making wood or transferring carbon into the soil. The wood may stand for
centuries inside a living tree, and it is slow to decay even when the tree
dies.
But the carbon in wood is vulnerable to rapid release. If a forest
burns down, for instance, much of the carbon stored in it will re-enter the
atmosphere.
Destruction by fires and insects is a part of the natural history of
forests, and in isolation, such events would be no cause for alarm. Indeed,
despite the recent problems, the new estimate, published Aug. 19 in the journal Science,
suggests that when emissions from the destruction of forests are subtracted
from the carbon they absorb, they are, on balance, packing more than a billion
tons of carbon into long-term storage every year.
One major reason is that forests, like other types of plants, appear
to be responding to the rise of carbon dioxide in the atmosphere by growing
more vigorously. The gas is, after all, the main food supply for plants.
Scientists have been surprised in recent years to learn that this factor is
causing a growth spurt even in mature forests, a finding that overturned
decades of ecological dogma.
Climate-change contrarians tend to focus on this “fertilization
effect,” hailing it as a boon for forests and the food supply. “The ongoing
rise of the air’s CO2 content is causing a great greening of the Earth,” one
advocate of this position, Craig D. Idso, said at a contrarian meeting in
Washington in July.
Dr. Idso and others assert that this effect is likely to continue for
the foreseeable future, ameliorating any negative impacts on plant growth from
rising temperatures. More mainstream scientists, while stating that CO2
fertilization is real, are much less certain about the long-term effects,
saying that the heat and water stress associated with climate change seem to be
making forests vulnerable to insect attack, fires and many other problems.
“Forests take a century to grow to maturity,” said Werner A. Kurz, a
Canadian scientist who is a leading expert on forest carbon. “It takes only a
single extreme climate event, a single attack by insects, to interrupt that
hundred-year uptake of carbon.”
It is possible the recent die-backs will prove transitory — a
coincidence, perhaps, that they all occurred at roughly the same time. The more
troubling possibility, experts said, is that the die-offs might prove to be the
leading edge of a more sweeping change.
“If this were happening in just a few places, it would be easier to
deny and write off,” said David A. Cleaves, senior adviser for the United
States Forest Service. “But it’s not. It’s happening all over the place. You’ve
got to say, gee, what is the common element?”
Tracking an Ebb and Flow
So far, humanity has been lucky. While some forests are starting to
release more carbon than they take up, that effect continues to be outweighed
by forests that pack carbon away. Whether those healthy forests will predominate
over coming decades, or will become sick themselves, is simply unclear.
The other day, deep in a healthy New England thicket of oaks, maples
and hemlocks, two young men scrambled around on their hands and knees measuring
twigs and sticks that had fallen from the trees.
“What was the diameter on that?” asked Jakob Lindaas, a Harvard
student holding a pencil and clipboard.
Leland K. Werden, a researcher at the university, called out a metric
measurement, and they moved to the next twig. It was one of thousands they
would eventually have to measure as part of an effort to tell how fast the
wood, knocked off the trees in an ice storm in 2008, was decaying.
The debris they were cataloging would not have struck a hiker as
anything to notice, much less measure, but the Harvard Forest, 3,000 acres near
Petersham, Mass., is one of the world’s most intensively studied patches of
woods. The work the men were doing will become a small contribution toward
solving one of the biggest accounting problems of modern science.
In every forest,
carbon is constantly being absorbed as trees and other organisms grow, then
released as they die or go dormant. These carbon fluxes, as they are called, vary through the
day. They vary with seasons, with climate and weather extremes, with the health
of the forests and with many other factors. Across the world, scientists are
struggling to track and understand this ebb and flow.
A 100-foot tower
stands in the middle of the Harvard Forest, studded with instruments. Put up in
1989, it was the first permanent tower of its kind in the world, built to help
track the carbon fluxes. Now hundreds
of them dot the planet.
Meticulous measurements over the decades have established that the
Harvest Forest is gaining weight, roughly two tons per acre per year, on
average. It is characteristic of a type of forest that is playing a big role in
limiting the damage from human carbon emissions: a recovering forest.
Not so long ago, the land was not a forest at all. Close to where the
men were working stood an old stone fence, a telltale sign of the land’s
history.
“When the European colonists came to America, they saw trees, and they
wanted fields and pastures,” explained J.
William Munger, a Harvard research fellow who was supervising the measurements.
So the colonists chopped down the original forest and built farmhouses, barns,
paddocks and sturdy stone fences.
By the mid-19th century, the Erie Canal and the railroads had opened
the interior of the country, and farmers plowing the thin, stony soils of New
England could not compete with produce from the rich fields of the Midwest. So
the old fields were abandoned, and trees have returned.
Today, the re-growing forests of the Eastern United States are among
the most important carbon sponges in the world. In the Harvard Forest, the rate
of carbon storage accelerated about a decade ago. As in much of the world, the
temperature is warming there — by an average of 2.3 degrees Fahrenheit in the
last 40 years — and that has led to longer growing seasons, benefiting this
particular forest more than hurting it, at least so far.
“We’re actually seeing that the leaves are falling off the trees later
in the fall,” Mr. Werden said.
Scientists say that something similar may be happening in other
forests, particularly in cold northern regions that are warming rapidly. In
some places, the higher temperatures could aid tree growth or cause forests to
expand into zones previously occupied by grasslands or tundra, storing more
carbon.
Forests are re-growing on abandoned agricultural land across vast
reaches of Europe and Russia. China, trying to slow the advance of a desert,
has planted nearly 100 million acres of trees, and those forests, too, are
absorbing carbon.
But, as a strategy for managing carbon emissions, these recovering
forests have one big limitation: the planet simply does not have room for many
more of them. To expand them significantly would require taking more farmland
out of production, an unlikely prospect in a world where food demand and prices
are rising.
“We’re basically running out of land,” Dr. Kurz said.
Even in forests that are relatively healthy now, like those of New
England, climate risks are coming into focus. For instance, invasive insects
that used to be killed off by cold winters are expected to spread north more
readily as the temperature warms, attacking trees.
The Harvard Forest has already been invaded by an insect called
the woolly adelgid that kills hemlock trees, and managers there fear a large
die-off in coming years.
Wildfires and Bugs
Stripping the bark of a tree with a hatchet, Diana L. Six, a University of Montana insect
scientist, pointed out the telltale signs of infestation by pine beetles:
channels drilled by the creatures as they chewed their way through the juicy part
of the tree.
The tree she was pointing out was already dead. Its needles, which
should have been deep green, displayed the sickly red that has become so
commonplace in the mountainous West. Because the beetles had cut off the tree’s
nutrients, the chlorophyll that made the needles green was breaking down,
leaving only reddish compounds.
Pine beetles are a natural part of the life cycle in Western forests,
but this outbreak, under way for more than a decade in some areas, is by far
the most extensive ever recorded. Scientists say winter temperatures used to
fall to 40 degrees below zero in the mountains every few years, killing off
many beetles. “It just doesn’t happen anymore,” said a leading climate
scientist from the University of Montana, Steven W. Running, who was surveying the scene
with Dr. Six one recent day.
As the climate has warmed, various beetle species have marauded across
the landscape, from Arizona to Alaska. The situation is worst in British
Columbia, which has lost millions of trees across an area the size of
Wisconsin.
The species Dr. Six was pointing out, the mountain
pine beetle, has pushed farther north into Canada than ever
recorded. The beetles have jumped the Rocky Mountains into Alberta, and fears
are rising that they could spread across the continent as temperatures rise in
coming decades. Standing on a mountain plateau south of Missoula, Dr. Six and
Dr. Running pointed to the devastation the beetles had wrought in the forest
around them, consisting of a high-elevation species called whitebark pine.
“We were going to try to do like an eight-year study up here. But
within three years, all this has happened,” Dr. Six said sadly.
“It’s game over,” Dr. Running said.
Later,
flying in a small plane over the Montana wilderness, Dr. Running said beetles
were not the only problem confronting the forests of the West.
Warmer temperatures
are causing mountain snowpack, on which so much of the life in the region
depends, to melt earlier in most years, he said. That is causing more severe
water deficits in the summer, just as the higher temperatures cause trees to
need extra water to survive. The whole landscape dries out, creating the
conditions for intense fires. Even if the landscape does not burn, the trees
become so stressed they are easy prey for beetles.
From the plane, Dr.
Running pointed out huge scars where fires had destroyed stands of trees in
recent years. “Nothing can stop the wildfires when they get to this magnitude,”
he said. Some of the fire scars stood adjacent to stands of lodgepole pine
destroyed by beetles.
At the moment, the most severe problems in the nation’s forests are
being seen in the Southwestern United States, in states like Arizona, New
Mexico and Texas. The region has been so dry that huge, explosive fires
consumed millions of acres of vegetation and thousands of homes and other
buildings this summer.
This year’s drought came against the background of an overall warming
and drying of the Southwestern climate, which scientists say helps to explain
the severe effects. But the role of climate change in causing the drought
itself is unclear — the more immediate cause is an intermittent weather pattern
called La Niña, and research is still under way on whether that cycle is being
altered or intensified by global warming, as some researchers suspect. Because
of the continuing climatic change, experts say some areas that are burning this
year may never return as forest — they are more likely to grow back as
heat-tolerant grass or shrub lands, storing far less carbon than the forests
they replace.
“A lot of ecologists like me are starting to think all these agents,
like insects and fires, are just the proximate cause, and the real culprit is
water stress caused by climate change,” said Robert L. Crabtree, head of a center
studying the Yellowstone region. “It doesn’t really matter what kills the trees
— they’re on their way out. The big question is, Are they going to regrow? If
they don’t, we could very well catastrophically lose our forests.”
Stalled Efforts
Scientists are coming to a sobering realization: There may be no such
thing left on Earth as a natural forest.
However wild some of them may look, experts say, forests from the
deepest Amazon to the remotest reaches of Siberia are now responding to human
influences, including the rising level of carbon dioxide in the air, increasing
heat and changing rainfall patterns. That raises the issue of what people can
do to protect forests.
Some steps have already been taken in recent years, with millions of
acres of public and private forest land being designated as conservation
reserves, for instance. But other ideas are essentially stymied for lack of
money.
Widespread areas of pine forest in the Western United States are a
prime example. A scientific consensus has emerged that people mismanaged those
particular forests over the past century, in part by suppressing the mild
ground fires that used to clear out underbrush and limit tree density.
As a consequence, these overgrown forests have become tinderboxes that
can be destroyed by high-intensity fires sweeping through the crowns. The
government stance is that many forests throughout the West need to be thinned,
and some environmental groups have come to agree.
But the small trees and brush that would be removed have a low
commercial value, especially in a weak economy. With little money available to
subsidize the thinning, the Forest Service is reduced to treating only small
sections of forest that pose the biggest threat to life and property.
On an even larger scale, experts cite a lack of money as endangering a
program to slow or halt the destruction of
tropical forests at human hands.
Deforestation, usually to make way for agriculture, has been under way
for decades, with Brazil and Indonesia being hotspots. The burning of tropical
forests not only ends their ability to absorb carbon, it also produces an
immediate flow of carbon back to the atmosphere, making it one of the leading
sources of greenhouse gas emissions.
Rich countries agreed in principle in recent years to pay poorer
countries large amounts of money if they would protect their forests.
The wealthy countries have pledged nearly $5 billion, enough to get
the program started, but far more money was eventually supposed to become
available. The idea was that the rich countries would create ways to charge
their companies for emissions of carbon dioxide, and some of this money would
flow abroad for forest preservation.
Climate legislation stalled in the United
States amid opposition from lawmakers worried about the economic effects, and
some European countries have also balked at sending money abroad. That means it
is not clear the forest program will ever get rolling in a substantial way.
“Like any other scheme to improve the human condition, it’s quite
precarious because it is so grand in its ambitions,” said William Boyd, a University of Colorado law
professor working to salvage the plan.
The best hope for the program now is that California, which is intent
on battling global warming, will allow industries to comply with its rules
partly by financing efforts to slow tropical deforestation. The idea is that
other states or countries would eventually follow suit.
Yet, scientists emphasize that in the end, programs meant to conserve
forests — or to render them more fire-resistant, as in the Western United
States, or to plant new ones, as in China — are only partial measures. To
ensure that forests are preserved for future generations, they say, society
needs to limit the fossil-fuel burning that is altering the climate of the
world.
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