Forests and the Atmosphere: New NCAR Experiment
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“Forests help control the atmosphere, and there’s a big difference
between the impacts of a living forest and a dead forest,” says NCAR
scientist Alex Guenther, a principal investigator on the project. “With
a dead forest, we may get different rainfall patterns, for example.”
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National Science Foundation
Press Release 08-162
Pine Bark Beetles Affecting More than Forests
September 24, 2008
Pine bark beetles appear to be doing more than killing large swaths
of forests in the Rocky Mountains. Scientists suspect they are also
altering local weather patterns and air quality.
A new international field project, led by scientists at the National
Center for Atmospheric Research (NCAR) in Boulder, Colo., is
exploring how trees and other vegetation influence rainfall,
temperatures, smog and other aspects of the atmosphere.
Plants take in and emit chemicals that affect the air, and they also
absorb varying amounts of incoming heat from the sun. When portions
of a forest die, the local atmosphere can change in subtle ways.
“Forests help control the atmosphere, and there’s a big difference
between the impacts of a living forest and a dead forest,” says NCAR
scientist Alex Guenther, a principal investigator on the project.
“With a dead forest, we may get different rainfall patterns, for
example.”
Launched this summer, the field project is scheduled to continue for
four years over a region extending from southern Wyoming to northern
New Mexico. Scientists plan to use aircraft and ground-based
instruments, as well as computer models, to study interactions
between the planet’s surface and the atmosphere.
The project, known as BEACHON (Bio-hydro-atmosphere interactions of
Energy, Aerosols, Carbon, H2O, Organics and Nitrogen), is funded by
the National Science Foundation (NSF), NCAR’s sponsor.
BEACHON will allow scientists to glean insights into such topics as
cloud formation, climate change, and the cycling of gases and
particles between the land and the atmosphere, according to Cliff
Jacobs, program director in NSF’s Division of Atmospheric Sciences.
Plants emit water vapor, other gases, and microscopic particles that
influence the atmosphere in subtle and complex ways. For example,
some tiny airborne particles from plants rise into clouds and seed
them, providing a surface for water droplets to adhere to and develop
into raindrops.
Greenhouse gases such as carbon dioxide (CO2), which is emitted in
large quantities from beetle-devastated forests, combine with extra
CO2 produced by human activities to influence the amount of heat from
the Sun that reaches Earth or gets reflected back into space.
Plants also emit chemicals known as volatile organic compounds that
can interact with human-caused pollution to influence the formation
of ground-level ozone, or smog, which affects both air quality and
local temperatures.
When large areas of trees are killed by pine beetles or other causes,
these interactions are disrupted. This may change cloud and
precipitation patterns for a decade or more, which can, in turn,
further alter the land cover.
Preliminary computer modeling suggests that beetle kill can lead to
temporary temperature increases of about 2-4 degrees Fahrenheit. This
is partly because of a lack of foliage to reflect the Sun’s heat back
into space.
Scientists also believe that beetle kill stimulates trees to release
more particles and chemicals into the atmosphere as they try to fight
off the insects. This worsens air quality, at least initially, by
increasing levels of ground-level ozone and particulate matter.
Wildfires, clearcutting, and new development also affect the
atmosphere by removing vegetation. But the impacts in each case can
vary significantly, depending on the remaining vegetation and changes
to soil conditions.
The exchange of gases and particles between the surface and the
atmosphere is critical in arid areas such as the western United
States.
Even slight changes in precipitation can have significant impacts on
the region.
“Here in the western United States, it is particularly important to
understand these subtle impacts on precipitation,” Guenther says.
“Rain and snow may become even more scarce in the future as the
climate changes, and the growing population wants ever more water.”
While other field projects have measured emissions from plants,
BEACHON is unusual because it will continue for at least four years
and cover an entire region.
This will allow researchers to examine the impacts of emissions in
different seasons and measure year-to-year changes.
To conduct measurements, researchers plan to use specially equipped
aircraft as well as towers that reach above the forest canopy to
measure emissions at up to about 100 feet above the ground.
Additional observations will come from a variety of soil and moisture
sensors, instruments for gases and tiny particles, radars, and
lidars, which are radar-like devices that use light instead of radio
waves.
“BEACHON will give us a very comprehensive picture of a forest’s
impact on the atmosphere,” Guenther says. “But at this point, we
don’t know what the project will reveal. We may end up with more
questions than answers.”
Organizations participating in the project include Colorado College,
Colorado State University, Cornell University, Texas A&M University,
and the universities of Colorado, Idaho, Minnesota, New Hampshire,
and Washington, as well as the U.S. Forest Service, the Environmental
Protection Agency, and universities in Austria, France and Japan.
-NSF-
Media Contacts
Cheryl Dybas, NSF (703) 292-7734 cdybas@nsf.gov
David Hosansky, NCAR (303) 497-8611 hosansky@ucar.edu
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fields of science and engineering, with an annual budget of $6.06
billion. NSF funds reach all 50 states through grants to over 1,900
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competitive requests for funding, and makes over 11,500 new funding
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Last Updated: September 24, 2008
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