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Executive Summary
The Ecosystems Panel was established by the National Research Council in
response to a request from the United States Global Change Research Program
(USGCRP). One of the panel's tasks was to review the ecosystems aspects
of the USGCRP's research program; that is the focus ofthis report. The panel
first identified the most significant and challenging areas in ecosystem sci-
ence, then used the areas identified to make recommendations to the
USGCR]'.
The panel used a broad definition of global change, as the USGCRP
does. By global change we refer to the interactions between natural changes
in the Earth's physical and biological structure and the broader effects of
human activities. Global change, therefore, has natural and anthropogenic
components. It occurs at all scales, but this report focuses on changes that,
when aggregated, are significant at a global scale, affecting the health, wel-
fare, and well-being of humans and other members of the biota. Examples of
global changes the panel judged to be significant include conversion of natural
landscapes (including coasts) to agricultural and urban ones; intensification
of various nutrient cycles; biotic mixing, including the introduction of nonna-
tive species into many ecosystems worldwide and the loss of other species;
changes in the hydrological cycle; changes in the climate due to human-
caused changes in atmospheric chemistry; changes in the size and distribution
of human populations; the conversion of natural landscapes to provide
transportation infrastructure such as roads, railways, harbors, and airports; and
the greenhouse gases emitted by vehicles using that infrastructure.
The panel developed a conceptual model (see Chapter 3) to focus its
assumptions and guide its recommendations. The model shows that humans
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2
GEOBAL CHANGE ECOSYSTEMS RESEARCH
have many effects on the environment that lead to global change. Climate is
one mechanism through which human activities affect their environment, and
continuing the research on climate and related phenomena is crucial to further
understand these interactions. But other mechanisms operate without direct
involvement of climate and also are important. Thus, to understand global
change, much research that does not focus on climate is needed in addition to
the current efforts on cTimate-related phenomena.
To evaluate the scientific questions that arise from considering the
conceptual model, the panel considered the importance of each factor that
produces environmental effects in the model, whether there are areas in which
understanding ofthe factors in the model end their effects are impeded by lack
of scientific knowledge, and the degree to which each scientific research topic
would be likely to lead to large progress on other, related topics.
The panel recommends a research initiative that comprises efforts to
understand four areas of global change research: (a) biogeochemical Cycles,
(b) Habitat changes (land cover and use), (c) Invasive species (biotic mixing),
and (~) Ecosystem Functioning and biological diversity (CmEF). Because
ecosystem functioning and biological diversity are relevant to and are affected
by cycles, habitat, and invasions, they are discussed under each ofthose three
major topics, rather than separately.
Biogeochemical cycles—especially cycles of carbon, nitrogen, phospho-
rus, and water have been pervasively affected by humans, resulting in
significant global changes. These changes have altered the composition of
plant and animal communities and ecosystem functioning, and have caused
changes in climate and in the quality of humans' lives. The various cycles
interact in complex ways; better understanding of them is needed, including
the role of the oceans in the cycles and the responses of ecosystems to changes
in them.
Habitat is a requirement for all species, and habitat Toss and degradation
accounts for more species extinctions than any other cause. The main cause
of global habitat loss and degradation is human use of the land: changes in
land use and land cover are important global changes. It thus is important to
understand current global patterns and rates of change in land use and land
cover and build on that understanding to predict future changes. it also is
important to understand the interactions between human activities and ecosys-
tem services.
The Earth's biotic mix the kinds and proportions of the species in an
ecosystem, including extinctions and introductions has been changing at an
accelerating pace. Introduction of nonnative species is the second-largest
cause of species extinction, and this global change affects almost every
ecosystem and many aspects of human life. We need to understand how to
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EXECUTIVE SUMMARY
3
predict whether a given species is likely to be introduced, to survive, and to
become established in a new environment, and whether it will cause large
effects. We need to understand why some introduced species remain harmless
for many generations and then suddenly begin spreading rapidly. Other
important research questions involve the role of genetic change in the ability
of an introduced species to spread and how the presence of introduced species
will affect the structure and functioning of ecosystems.
Mounting a large, coordinated, and sustained effort to understand aspects
of global change not emphasized in the current cTimate-related research
agenda is a significant undertaking, but it is essential to understand, predict,
and deal with the major global changes that have already occurred and whose
pace seems likely to accelerate. Because the subject areas of CHIEF and the
current activities of the USGCRP complement one another, work on CHIEF
will strengthen the USGCRP and can be accomplished without major struc-
tural changes to the administration of the USGCRP.
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Representative terms from entire chapter:
land cover
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