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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 cyclesespecially 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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