and Biogeochemistry of Ecosystems
USGCRP agencies are continuing
efforts to build a strong interagency focus on global change impacts on
managed and natural ecosystems, and to understand the relationship between
a changing biosphere and a changing climate. The primary goal of the ecosystems
program element is to provide a stronger scientific basis for understanding,
predicting, and responding to the consequences of global environmental
changes, of both natural and human origin, in terrestrial, aquatic, coastal,
and marine ecosystems. Also under study is how these changes affect ecosystems’
ability to provide goods and services and support sustained use. USGCRP
ecosystems research activities will be closely coordinated with the research
that is being undertaken by the CENR Subcommittee on Ecological Systems,
including the newly emerging efforts under the Administration’s Integrated
Science for Ecosystem Challenges (ISEC) initiative. Cooperation in the
development and implementation of USGCRP and ISEC research strategies is
particularly important for investigating the effects of multiple stresses
on U.S. ecosystems, which is a priority for each.
The biosphere consists of diverse ecosystems that vary widely in complexity
and productivity, in the extent to which they are managed, and in their
value to society. Ecosystems directly provide forage, timber, fish, food,
and fiber, as well as other services such as water cycling, climate regulation,
recreational opportunities, and wildlife habitat. The proper functioning
of ecosystems and sustained use of natural resources may be threatened
by a number of global environmental changes. Some of the stresses or disturbances
that have the greatest immediate potential to affect ecosystems adversely
and alter their capability to support humanity include: changing land use
and land cover; direct effects of rising CO2; changes in global nitrogen
cycles; and species invasions. Moreover, subjecting ecosystems to one or
more of these stresses simultaneously may have a significant negative impact
on ecosystem function.
Figure 2. Potential
Changes in Distribution of Douglas Fir.
(See Appendix E for additional information)
key challenges can be readily described, the ecosystems program does not
easily lend itself to the development and implementation of a focused strategy
for research on ecosystem impacts. In addition, limited resources constrain
the number and diversity of important ecosystems that can be analyzed;
data bases from representative ecosystems are often lacking, yet crucial
to modeling and predicting ecosystem responses to multiple global environmental
changes; and experimental facilities for investigating the combined effects
of multiple factors on intact ecosystems need to be strengthened.
Changing Land Use and Land Cover: Greater understanding
is needed of the relationships among land cover, land use, climate, and
weather, particularly how changing land use and land cover affect local
and regional climate, and how changing temperatures, altered patterns and
amounts of precipitation, and increased variability in weather affect major
terrestrial and marine ecosystems. The effects of changes in land use on
land cover, ecosystem services, hydrologic cycles, species distribution,
biodiversity, and human social and economic systems also need study.
Multiple Stresses in Ecosystems: Ecosystems subjected
to more than one stress — either simultaneously or sequentially — may respond
in ways qualitatively different from that which would be expected from
an examination of single stresses. The dynamics of multiple stresses, and
the possibility of, and indicators for, "threshold" responses in ecosystems
that lead to sudden and dramatic change in ecosystem structure and function,
must be better understood. Improvements also are needed in the capability
to observe and develop a predictive understanding of effects of multiple,
interacting environmental changes, such as combined effects of elevated
CO2 and reduced availability of water in terrestrial ecosystems.
Changes in the Global Nitrogen Cycle: Humans have
significantly impacted the global nitrogen cycle, doubling the rate at
which atmospheric nitrogen (which most organisms cannot use directly) is
converted into a nutrient form that can be used by many organisms. These
amounts of nitrogen in terrestrial ecosystems can affect the productivity
of plants and cause shifts in the types of species present in the ecosystems,
and may also, in some cases, stimulate carbon storage.
for FY 2000:
The USGCRP will continue developing and publishing inventories
and models of terrestrial ecosystems that will be used to better predict
how ecosystems are affected by multiple environmental stressors.
The USGCRP will document land-use and land-cover change in
regions where rapid change could potentially alter the sensitivities/vulnerabilities
of the region to climate change.
The USGCRP will examine how climate change, vegetation management
practices, and disturbance affect the spread of exotic plants and the regeneration
of native plants at high elevations.
The USGCRP will understand the influence of changing precipitation
and nutrient cycling patterns on species regeneration and composition,
and the resulting consequences for forest growth, decomposition processes,
carbon sequestration, and sustainability.
The USGCRP will develop and apply, using tools of molecular
biology, gene probes for key enzymes linking the carbon and nitrogen cycles
in marine microbes.
The USGCRP will develop methods that assess the invasiveness
of nonindigenous species by combining the science of landscape ecology
with the principles of risk assessment. The program will use these methods
to identify those areas in the U.S. that may be vulnerable to nonindigenous
species invasion due to climate change and variability.
Using ecosystem-scale experiments involving increased CO2
and other environmental factors, the USGCRP will determine how atmospheric
change and potential climatic change may affect forest productivity, forest
health, and species distributions.