As if the only reason we should plant trees is to sequester carbon!
[from the NYT]
May 24, 2001
Studies Challenge Role of Trees in Curbing Greenhouse Gases
By 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/.
