Global Change Ecosystems Research (2000) / Chapter Skim
Currently Skimming:
The Panel's Advice to the USGCRP
The Panel's Advice to the USGCRP
Pages 16-37
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From page 16... ...
reflects that emphasis, although it makes strong recommendations that more attention be paid to biological diversity, and its recommendation for more research on carbon and nitrogen cycles includes a strong recommendation for research on how those cycles directly affect ecosystems. The Ecosystems Pane]
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, Invasive species (biotic mixing) , and Ecosystem Functioning (CHIEF)
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Much better understanding of nitrogen and phosphorus cycles is needed, including the role of the oceans in the cycles, the response of natural ecosystems to nitrogen and phosphorus, and the interactions between them. Hydrologic cycles have been profoundly altered and aquatic ecosystems have been altered or destroyed by human activities (Data!
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From page 19... ...
In terrestrial systems, plants often store more carbon energy and biomass in the presence of increased phosphorus and nitrogen, especially when atmospheric CO2 is increased as well. Nitrogen Deposition and Global Changes Of the major global changes, human impacts on the nitrogen cycle are among the most significant.
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1997~. Elevated CO2 and Global Changes Observed and projected increases in atmospheric CO2 will have direct physiological effects on plants but not on animals.
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Biogeochemical and Hydrologic Cycles and Potentially Harmful Substances: Interactions with Biological Diversity and Ecosystem Functioning These cTimate-related issues are addressed in Chapter 2 ofthe Pathways report, here the emphasis is on the ecosystem structure and functioning rather than on the carbon budget. These factors affect biological diversity and functioning primarily at local end regional scales but occur globally.
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The composition and structure of terrestrial ecosystems feeds back on the hydrologic cycle through ecosystem functioning, including patterns of evapotranspiration, and through canopy interception, infiltration, storage, and runoff. Biological diversity is frequently greatest at soil moistures midway between soil drought and saturated conditions, when there is little seasonal pattern in moisture distributions, and when predictability of soil moisture is high.
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Human activities have caused significant transiocation of soil nutrients to groundwater and surface runoff, in some systems through poor irrigation management, irrigation with high salinity water sources, and excessive fertilizer inputs, which cause additions and enhancements of nutrients to downsiope and downstream systems. For example, the hypoxic zone in the Gulf of Mexico is presumed to be brought about by agriculture in the Mississippi River watershed (Moffat ~ 998; Mississippi River/GulfofMexico Watershed Nutrient Task Force web site available at http://www.nos.noaa.gov/ products/pubs_hypox.htmI)
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These challenges expand markedly when the context shifts from only elevated CO2 to a broader array of global changes. For example, developing the capacity to predict changes in disturbance regimes, especially fire, presents a suite of challenges different from those posed by elevated CO2.
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How will elevated atmospheric CO2 and anthropogenic acceleration of the nitrogen and phosphorus cycles interact with other elements of global change, especially climate change and biotic mixing, to alter the future trajectory of primary production and the species composition of terrestrial, aquatic, and marine ecosystems?
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Land-cover changes have profound global effects because they are so pervasive and have such strong influences on biological diversity and ecosystem functioning. Human activities have strong effects on land use and land cover.
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Each of these changes can influence biodiversity. indeed, global land-use change can be considered as an enormous uncontrolled experiment in how habitat changes influence the biota and ecosystem functioning.
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For example, the environment may be changed directly when fire control and logging after the frequency and extent of natural fires. Natural disturbances create and maintain biodiversity by creating a mosaic of habitats; in general, the chances of losing native species and disrupting ecological functioning increase when the patterns of natural habitats are altered (Turner et al.
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Ecosystem Functioning Land use and management often have a direct influence on nutrient and water cycling and soil quality. For example, agricultural practices often add nutrients in fertilizer and water by means of irrigation.
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Are there thresholds in land-cover patterns (e.g., connectivity of habitats or sizes of patches) beyond which large changes in biodiversity and ecosystem functioning are likely to occur?
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, with a variety of potential impacts on biological diversity and ecosystem functioning. When they become established, such invaders can eliminate particular native species, either globally or locally, through a variety of means.
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Just three introduced tree species in south Florida form nearly monospecific stands over nearly 600,000 ha (Schmitz et al.
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While it is clear that if enough species are lost, ecosystem functioning will be impaired, it is not clear how many species are "enough," and in general how the kinds and numbers of species in an ecosystem affect a variety of ecological processes. Because human activities are affecting both the number and kinds of species in most ecosystems, especially terrestrial and freshwater ones, this general scientific question assumes heightened importance and urgency in any global change research program.
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dominates 7 million ha of rangeland in Idaho and Utah alone, not by overgrowing native plants, but by facilitating fires and by having a deep taproot, as opposed to the shallow root mass of the natives. Once established by virtue of its impact on the fire regime and hydrology, cheatgrass replaces native plants and populations of many animals subsequently plummet (Westbrooks 1998~.
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To what degree are lessons learned from the evolution of virulence in pathogenic disease vectors transferable to the understanding of genetic changes leading to invasiveness or to increased invasiveness after an exotic becomes established?
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A CHIEF research initiative would do for ecological research what the USGCRP has done for atmospheric research: it would stimulate and better coordinate, at the highest administrative level, agency research programs in nutrient cycles, habitat changes, invasive species, and ecosystem functioning.
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THE PANEL S ADVICE TO THE USGCRP 37 Recent progress has been so rapid, and the need for integration is so great, that the identity of key questions and the boundaries between disciplines need to be flexible at a level that has never been required in the past. The world is changing too rapidly for science to address the challenges of global change with traditional, incremental approaches.
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