December
13, 2006 On December 11, USDA
Forest
Service (FS) scientists from the FS Southern Research Station (SRS)
unit in
Research Triangle Park, NC, along with colleagues from Duke University,
published
two papers in The Proceedings of the
National Academy of Sciences (PNAS) that provide a more
precise
understanding of how forests respond to increasing atmospheric
concentrations
of carbon dioxide [CO2], the major greenhouse gas driving climate
change. Building on
preliminary studies
reported in Nature, the researchers found that trees can only increase
wood
growth from elevated [CO2] if there is enough leaf area to support that
growth.
Leaf area, in turn, is limited by soil nutrition; without adequate soil
nutrition, trees respond to elevated [CO2] by transferring carbon below
ground,
then recycling it back to the atmospheric through respiration. "With sufficient
soil
nutrition, forests increase their ability to tie up, or sequester
carbon in
woody biomass under increasing atmospheric [CO2] concentrations," says
Kurt Johnsen, SRS researcher involved in the project. "With lower soil
nutrition, forests still sequester carbon, but cannot take full
advantage
increasing [CO2] levels. Due to land use history, many forests are
deficient in
soil nutrition, but forest management -- including fertilizing with
nitrogen --
can greatly increase growth rate and wood growth responses to elevated
atmospheric [CO2]." The studies took
place at a Free
Air Carbon Enrichment (FACE) study established by the U.S. Department
of Energy
on the The researchers
further tested
their hypotheses using data from FACE sites in "Forests play a
critical
part in sequestering carbon, and may play a role in mitigating the
elevated
levels of carbon dioxide associated with climate change," says Johnsen.
"To predict how much forests can sequester, we need accurate ways to
predict
what happens to carbon within forest systems and how this partitioning
is
affected by environmental conditions."
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