05/26/01 -- Role of Trees in Curbing Greenhouse Gases Challenged

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FOREST CONSERVATION NEWS TODAY

Role of Trees in Curbing Greenhouse Gases Challenged

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05/26/01

OVERVIEW & COMMENTARY by Forests.org

Two new studies call into question the role of trees and soils as

long-term carbon sinks. It was found that forests initially

capitalize on extra carbon dioxide in the atmosphere, but they

quickly deplete nutrients in the soil. Forest growth then slows

dramatically and the ability to store excess carbon is curtailed.

The results suggest that planting trees may not thwart global warming

or serve as an adequate substitute for reducing heat-trapping

greenhouse gas emissions. The findings do not mean planting trees

is not important - both for their carbon storage and other

environmental benefits. But it is becoming clear that plantations

are not a climate change panacea, and that we cannot look to planted

forests to eliminate the threat of global warming. The only climate

change policies guaranteed to significantly reduce the rate of growth

of atmospheric carbon dioxide is vigorously cutting emissions and

maintaining old-growth forest ecosystems.

g.b.

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ITEM #1

Title: Studies Challenge Role of Trees in Curbing Greenhouse Gases

Source: New York Times

Date: May 24, 2001

Byline: ANDREW C. REVKIN

Two new studies are challenging the idea that planting forests

could be a cheap way to absorb emissions of carbon dioxide, the main

heat- trapping gas released by human activities.

In one, tracts of pine trees exposed to elevated levels of the gas

initially absorbed large amounts and had a short growth spurt, but

then reverted to typical growth rates.

A separate study of the soil around the exposed trees found that,

although it accumulated carbon, much of the carbon was released back

into the air as carbon dioxide when organic material in the soil

decomposed.

The studies, described in today's issue of the journal Nature, were

limited to loblolly pine forests in North Carolina, but the authors

said their findings suggested a limit to the value of forest planting

to counter carbon dioxide emissions from smokestacks and tailpipes

that many scientists say are warming

the climate.

"Such findings call into question the role of soils as long-term

carbon sinks," wrote the authors of the soil study, Dr. John Lichter,

a biologist at Bowdoin College, and Dr. William H. Schlesinger, a

professor of biogeochemistry at Duke University, which owns the

forest where the research was done.

Forest planting has figured in negotiations on a global agreement to

reduce greenhouse gases, and the United States, Canada, Japan and

some other large industrial countries have backed the idea.

But the new research suggests the approach is not as effective as

advocates had hoped. The study of tree growth, led by Dr. Ram Oren,

an ecologist at Duke, concluded that previous estimates of forests'

carbon-absorbing abilities were "unduly optimistic."

Several scientists not involved in the studies said the research

provided some of the first hard evidence showing the response of

trees to carbon dioxide and, among other things, should help improve

computer models used to predict how the rise in heat-trapping gases

might affect the climate and ecosystems.

Others added that the work challenges a longstanding assertion of

some coal and power companies that the main consequence of rising

levels of carbon dioxide in the air will not be a damaging warming of

the climate, but rather a flourishing of forests and other plant

life.

Some scientists stressed that the Duke findings - despite the years

of monitoring - still are preliminary because forests can take a long

time to adjust to changes in the environment, and the conditions

noted so far may only be a prelude to other shifts.

And some scientists involved in related experiments looking at the

absorption of the gas by croplands and grassland said they thought

that some of the researchers' conclusions were gloomier than their

data.

Dr. Bruce A. Kimball, a soil scientist who has studied the response

of wheat and cotton to elevated carbon dioxide at a Department of

Agriculture laboratory in Phoenix, noted that the Duke soil findings,

over all, still showed an increase in retained carbon. He said tree

planting could have "some significant impact on offsetting some of

our CO2 emissions."

He conceded, however, that the abrupt drop in the growth rate of the

trees was "discouraging."

The study is described on a Department of Energy Web site at

www.face.bnl.gov/.

ITEM #2

Title: Global Warming Carbon Experiments

Date: May 23, 2001

Byline: JOSEPH B. VERRENGIA, AP Science Writer

Experiments conducted in a North Carolina pine forest show that after

an initial growth spurt, trees grow more slowly and do not absorb as

much excess carbon from the atmosphere as expected.

The results suggest that planting trees may not thwart global warming

or serve as an adequate substitute for reducing heat-trapping

greenhouse gas emissions.

Forests typically grow in poor soils. Researchers said that once

forests have initially capitalized on the extra carbon in the

atmosphere, they quickly deplete nutrients in the soil. Their growth

slows dramatically and their ability to store excess carbon is

curtailed.

``The impact of existing forests on carbon in the atmosphere may not

last very long and it might not be very significant,'' said Duke

University ecologist Ram Oren, the lead researcher in one of the

studies.

``The forests' impact on carbon dioxide may not materialize in any

important way,'' he said.

Scientists who did not participate in the studies said results are

``potentially very important'' in determining the role of forests

play in regulating the changing climate.

``If this is true for forests in general, we may not be able to count

on existing forests to maintain a high capacity to absorb carbon,''

said University of Illinois plant biologist Evan DeLucia, who

conducted earlier experiments in the same plots.

``We cannot look to forests to eliminate the threat of global

warming,'' DeLucia said.

As plants grow, they absorb carbon dioxide in their tissues and emit

oxygen.

Carbon dioxide levels in the atmosphere have been increasing for

decades in conjunction with fossil fuel consumption, traffic and

industrialization.

Many scientists believe the rising levels of CO2 and other emissions

in the atmosphere are trapping more of the sun's heat, driving up

temperatures and causing global warming. Some computer projections

predict levels of these so-called greenhouse gases will rise 35 to 50

percent in the next 50 years, with temperatures increasing along with

them.

Conservationists have advocated protecting existing forests and

planting new ones so they can serve as ``carbon sinks'' that would

help to regulate the atmosphere and moderate global warming.

However, the pair of studies published in the latest issue of the

journal Nature suggests those hopes are too optimistic.

The experiments were conducted on experimental rings of Loblolly

pines near Duke University.

In one test plot, pipes steadily pumped an air mixture containing 560

parts per million of carbon dioxide into the tree canopy. It

simulated what computer models predict atmospheric conditions will be

in 2050.

In a control plot, pipes pumped conventional air with a carbon

dioxide level of about 365 ppm.

For two years, the trees exposed to more carbon dioxide grew at a

rate up to 25 percent faster. Those results were reported by DeLucia

in 1999.

Since then, Oren said, growth in the tree rings fumigated with extra

carbon dioxide slowed to about the same rate as the control trees.

Expectations that the trees would continue to sequester large amounts

of additional carbon were ``unduly optimistic,'' he said.

Oren blames the trees' return to slow growth on a shortage of other

nutrients, notably nitrogen. When the researchers added nitrogen to

the test plots, those trees grew quickly again.

Farming, air pollution and other activities are increasing the levels

of some forms of nitrogen in the environment. But those sources

probably would not directly fertilize forests to a meaningful degree,

the researchers said.

``Forests may slow down the rate of increase of carbon dioxide in the

atmosphere,'' Oren said. ``But most forests exhaust soil nutrients

very quickly. From that point on, the trees show no response.''

In the second study, researchers from Duke and Bowdoin College in

Brunswick, Maine, examined decomposing leaves and roots on the floor

of the experimental forest plots.

They found the total amount of litter increases in a carbon-dioxide-

enriched atmosphere, but so does the rate at which it is broken down.

The carbon returns to the atmosphere, rather than being incorporated

into the soil, reported William Schlesinger and John Lichter. Once a

leaf falls from the tree, its carbon is recycled back in the

atmosphere in about three years, they said.

The new studies were conducted in forest plots that are comprised

primarily of pine trees, although sweet gum and other native species

are moving in.

Researchers disagreed whether the results can be applied to other

regions, such as the tropics, where conditions and tree species are

different.

DeLucia said tropical forests may show even less response to elevated

carbon levels.

In a Nature commentary, Eric A. Davidson and Adam I. Hirsch of the

Woods Hole Research Center in Massachusetts said the results ``will

be essential'' in improving computer models that predict global

climate change.

ITEM #3

Title: Scientists Query Future Power of 'Carbon Sinks'

Date: May 23, 2001

Byline: Patricia Reaney

LONDON (Reuters) - Environmentalists who suggest forests can be used

to absorb excess carbon dioxide (CO2) accumulating in the Earth's

atmosphere and contributing to global warming may have to think

again.

Researchers at the University of Michigan and Duke University in

North Carolina have completed a seven-year study which raises doubts

about the ability of forests, so-called carbon sinks, to soak up the

excess CO2 being pumped into the atmosphere from exhaust pipes and

smoke stacks.

Using forests to fight global warming, a plan backed by the United

States, was one of the disputed points at the heart of the failed

U.N. climate conference in The Hague last year.

The new research by the American scientists shows a shortage of water

and nutrients in the soil could limit how trees respond to increases

in CO2.

``In terms of rising atmospheric CO2, I believe we need to consider

the fertility of the site when we are thinking about how much carbon

sequestration (absorption) we have now and how much we can project in

the future,'' David Ellsworth said in a telephone interview

Wednesday.

The finding does not change the situation very much for current

carbon sinks, he said, but it could have serious implications on

future predictions.

``If we are trying to value future carbon sinks, this could be

incredibly important in the sense that future carbon sinks may not be

as large as we have anticipated based on shorter-term studies and

modeling activities,'' Ellsworth added.

The assistant professor of plant physiological ecology and colleagues

examined the effects of elevated CO2 on forests with limited

nutrients over many years. They also exposed trees to increased CO2

to simulate conditions predicted in 50 years time.

ROLE OF SOIL ALSO QUESTIONED

Their results are reported in the current issue of science journal

Nature along with a study by other Duke scientists which questions

the role of soils as long-term carbon sinks.

Until now the impact of soil nutrients has not been considered as a

factor in a tree's ability to absorb CO2, but Ellsworth and his

colleagues said it should be.

``The debate over how much CO2 trees will absorb should consider the

limitations of soil fertility or other key resources in low supply,''

he said.

``It makes the playing ground a lot more complicated to evaluate,''

Ellsworth added.

The dispute between the European Union and the United States at the

climate talks was mainly over carbon sinks. The U.S. plan called for

developed nations to be allowed to count CO2 soaked up by forests

against targets for cutting greenhouse gas emissions.

Opponents of the scheme argued that it could lead to a rise in global

emissions.

``I don't think we can assume existing forests, with their fertility

limitations, will completely offset rising CO2 without soil

amendments,'' said Ellsworth.

``We will more likely find solutions in measures such as burning less

fossil fuel and planting more trees in high-nutrient soils,'' he

added.

But the scientists cautioned that adding nutrients to the soil may

involve other negative effects on the environment.

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