June 10th USGCRP Seminar Flyer on Forests - Final
tsocci at usgcrp.gov
Thu Jun 6 11:02:53 EDT 1996
U.S. Global Change Research Program Second Monday Seminar Series
FOREST RESPONSES TO CHANGES IN ATMOSPHERIC COMPOSITION AND CLIMATE
What is the response of forests to increasing concentrations of carbon
dioxide and other gases? What impact has climate change had on forests?
What are the combined effects of these influences on soil fertility, forest
productivity, and forest ecosystems? Do forests in different regions
exhibit different responses to these influences? What is the outlook for
forests 25 to 50 years from now, and beyond?
Monday June 10, 1996, 3:15-4:45 PM
Rayburn House Office Bldg., Room B369, Washington, DC
Dr. Jerry Sesco, Deputy Chief of Forest Service for Research, U.S.
Department of Agriculture (USDA), Washington, DC
Dr. Richard Birdsey, Program Manager, Northern Global Change Program, USDA
Forest Service, Radnor, PA
Dr. J. G. Isebrands, Project Leader, North Central Forest Experiment
Station, USDA Forest Service, Rhinelander, WI.
Carbon dioxide (CO2) is the most important of the greenhouse gases
that are influenced directly by human activities. The rising atmospheric
concentration of carbon dioxide is predicted to enhance photosynthesis of
some plants and to warm the climate. The CO2 concentration in the atmosphere is
determined by the emissions from combustion of fossil fuels and by CO2
uptake and release by the Earth's oceans, vegetation, and soils. Carbon
dioxide is taken up by land plants, which annually consume about twelve
times the world's fossil fuel emissions. The biosphere also gives off about
the same amout of CO2 through respiration and plant decay. This makes
land plants a critical part of the global carbon cycle.
Global observations clearly indicate atmospheric concentrations of CO2 are
increasing. However, the rate of increase in atmospheric CO2 is not as high
as expected based on the increase in fossil fuel emissions. This "missing"
carbon is being taken up by either the oceans or the terrestrial biosphere
(plants and soils), or both. Understanding these carbon transfers is
critical to predicting the importance of global climate change and its
consequences. Recent studies have pointed to carbon accumulation in
temperate forests of the Northern Hemisphere as a likely explanation for
the imbalance in the global carbon budget. It is thought that several
factors may be accounting for the increase in the carbon uptake by the
terrestrial biosphere - the regrowth of forests in regions where farming is
being reduced, increased plant growth due to the increase in the CO2
concentration of the atmosphere, and increased forest productivity as a
result of nitrogen deposition.
Atmospheric Changes and Forest Responses
Trees and ecosystems are affected by an array of environmental
factors that vary in space and time, and so a particularly important area
of research has been the simultaneous effects of multiple factors on
forests. While simple experiments may show the effects of a single factor,
it is the timing and intensity of interactions between multiple factors
that determine how a tree responds to environmental change. There are also
genetic factors that determine the sensitivity of individual trees to
stress, and their adaptability to a new environment.
It is generally accepted that scientists need to study more natural systems
because of significant difficulties with exposure chamber techniques. Under
the auspices of the U.S. Global Chnage Research Program, a multi-agency
terrestrial ecology program, augmented by funding from private sources, a
new chamberless experimental facility is under development at a U.S. Forest
Service site in Rhinelander, Wisconsin. This will be the largest "free air CO2
enrichment" (FACE) experimental facility in the U.S., consisting of 12 exposure
rings, several different tree species, and the capability to simulate exposures
to CO2 and ozone, singly and in combination.
In multi-factor, multi-year experiments using exposure chambers, different
tree species have shown very different responses to elevated ozone levels,
alone and in combination with elevated CO2 levels. For example, aspen is
highly sensitive to ozone and there are strong genotypic differences. Ozone
reduces biomass production and root growth in aspen, and an increase in the
CO2 concentration does not compensate for the reduction. This negative
interaction between CO2 and ozone decreases aspen photosynthesis rates more
than ozone stress alone. In contrast, white pine and yellow poplar show no
significant detectable adverse effects of exposure to ozone, and growth has
been stimulated with the simultaneous addition of CO2.
Models of Forest Behavior and Response
Integrated models of physical, biological, and social systems are
being used to address the effects of different scenarios of climate change
on forest productivity, carbon storage, and the timber economy. Initial
projections from these models suggest that increases in productivity are
likely for northern forest types, while southern forest types may show
small increases or decreases in productivity. In one extreme scenario for
the southeastern U.S., much of the dense pine forest would be replaced by a
pine savanna of low productivity. Forests in the western U.S. may be
highly sensitive to small climate changes because they often grow at or
near the limits of climate tolerated by tree species.
When the ecosystem models are linked with economic models, results show
that projected increases in productivity may not lead to increases in
harvest at the national scale because the market responds to many different
factors besides timber growth. The models project some redistribution of
harvest among regions, which would in turn lead to some changes in fiber
types and the ownership of lands from which wood is harvested. Harvested
timber will add to a growing pool of carbon in wood products. Byproducts
from timber production, which are burned for energy, reduce the combustion
of fossil fuels that adds long-stored carbon back into the atmosphere.
Retrospective applications of the models have explored uptake and release
of carbon by forests and forest products. Results suggest that U.S.
forests are currently a net sink for carbon. Increases in biomass on U.S.
forest lands over the last 40 years are estimated to have added 281 million
metric tons per year of stored carbon, enough to offset 25 percent of U.S.
emissions for the period. Most of this additional carbon is found in
regrowing forests on abandoned agricultural land in the eastern U.S. These
estimates indeed suggest that some of the "missing" carbon can be accounted
for by storage in northern temperate forests.
The integrated models are currently undergoing extensive revisions
in preparation for another round of projections based on updated forest
inventory data, new climate projections, and developments in modeling
techniques. An international model intercomparison study known as VEMAP
(Vegetation Ecosystem Model Analysis Project) has compared the results of 3
biogeochemistry models for simulating the response of 21 different U.S.
vegetation types to climate change scenarios. This exercise has helped the
model developers understand the strengths and weaknesses in representing
key ecosystems processes, and will facilitate analytical review of
uncertainty in projections of vegetation change.
Forest Management to Offset CO2 Emissions
Opportunities to increase carbon storage above the expected baseline have
been identified and are beginning to influence landowner decisions.
Studies have shown that CO2 emissions can be effectively offset by
sequestering additional carbon at various steps in the life cycle of wood
growth, harvest, use, and disposal. Typical practices to offset carbon
emissions include (1) tree planting on marginal agricultural land, (2)
increasing timber growth on forests now used for timber production, (3)
increasing the use of wood in place of fossil fuels, and (4) improving wood
Several U.S. agencies, in partnership with American Forests, a nonprofit
organization that represents many land owners, have been quantifying how
various management practices used in different regions and forest types may
impact carbon storage over long periods of time. This information has been
used by utility companies to design carbon offset projects to compensate
for CO2 emissions that are a byproduct of energy generation from fossil
fuels. Other landowners have begun to use estimates of carbon storage under
different forest conditions to quantify accomplishments under the
Department of Energy's "Voluntary Reporting of Greenhouse Gas Reductions"
Dr. Richard Birdsey is Program Manager of the Northern Global Change
Research Program within the U.S. Department of Agriculture, Forest Service,
Northeastern Forest Experiment Station. He is a specialist in quantitative
methods for large-scale forest inventories and has pioneered the
development of methods to estimate national carbon budgets for forest lands
from forest inventory data. He spent 10 years as team leader for forest
inventory research in the Midsouth States. He was a principal contributor
to several regional and national assessments of future timber supply in the
South and the Nation. He designed the first comprehensive inventories of
forest resources in Puerto Rico and St. Vincent, West Indies. He is a
contributor to the ongoing inventory of U.S. greenhouse gases and sinks
compiled by USDA, EPA, and DOE. He also cooperates with the Sukachev
Institute of the Russian Academy of Sciences in a project to estimate the
Russian carbon budget. He was a major contributor to the most recent
assessment of climate change impacts on America's forests conducted as part
of the decadal Resources Planning Act Assessment. In his current role as
Program Manager, Dr. Birdsey is coordinating a national effort to link
biological and economic models with atmospheric models to assess the
impacts of global change on U.S. forests, and to analyze mitigation and
adaptation strategies. He manages a large basic research program involving
a dozen U.S. Forest Service Laboratories and Experimental Forests in the
Northeast and North Central States, with research emphases on basic plant
processes, ecosystem nutrient cycling, and measurement and modeling
techniques. Dr. Birdsey has degrees in quantitative methods and world
forestry from the State University of New York, College of Environmental
Science and Forestry.
Dr. J. G. Isebrands is Project Leader of a research project in the USDA
Forest Service (FS), North Central Forest Experiment Station entitled
"Physiological mechanisms of growth and multiple stress responses in
northern forests" located in Rhinelander, Wisconsin. His research expertise
is tree physiology with emphasis on carbon allocation, tree canopy
architecture and physiological growth process modeling. He is currently the
FS representative to the Global Change and Terrestrial Ecosystems Core
Project (GCTE) of the International Geosphere-Biosphere Program (IGBP) as
well as the FS representative to the FAO-sponsored International Poplar
Commission. He was involved in the formation of the current FS Global
Change Program and is currently on the technical advisory committee of the
FS Northern Global Change Program. He has received an award from this group
for fostering cooperative research. For 8 years he was the chairman of the
International Union Forest Research Organization (IUFRO) Working Group on
"Forest tree canopies" and has been the cochairman of the international
meetings for that group in Italy, New Zealand, and the U.S. He currently
holds adjunct research professorships at four universities including
University of Minnesota, Michigan Tech University, University of
Washington, and Swedish University of Agricultural Sciences. He holds
graduate degrees in forestry and forest science from Iowa State University,
Ames, IA and is the author and/or co-author of over 100 scientific
PLANNED TOPIC FOR NEXT SEMINAR on Monday, July 15, 1996
A Look at Climate Feedbacks and Controls
For more information please contact:
Dr. Anthony D. Socci, U.S. Global Change Research Program Office
300 D St., SW, Suite 840, Washington, DC 20024
Telephone: (202) 651-8244; Fax: (202) 554-6715
E-Mail: TSOCCI at USGCRP.GOV.
Additional information on the U.S. Global Change Research Program (USGCRP)
and this Seminar Series is available on the USGCRP Home Page at:
http://www.usgcrp.gov. Normally these seminars are held on the second
Monday of each month.
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