Role of Terrestrial Ecosystems in Global Change A Plan for Action (1994) / Chapter Skim
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3 RESEARCH PROGRAM
3 RESEARCH PROGRAM
Pages 13-38
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From page 13... ...
. Until the current global carbon budget can be balanced, there is little hope of predicting future changes in atmospheric CO2 concentration and, therefore, the radiative properties of the atmosphere that will determine future climatic changes.
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From page 14... ...
These CO2 responses and their interactions with other environmental factors must also be known in order to predict future food and fiber production and, therefore, the human carrying capacity of the earth. Current Efforts The Global Change and Terrestrial Ecosystems (GCTE)
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From page 15... ...
The field experiments should be accompanied by efforts to improve geographically explicit regional models of ecosystem function and biogeochemistry, using remote-sensing data to extend experimental results to large areas. Research Program The research program outlined here is discussed in greater detail in international documents (IGBP, 1990a, 1992)
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From page 16... ...
Critical measurements include gross primary production, net primary production, changes in soil and plant carbon storage, litter quality, carbon and nitrogen mineralization by soil microbes, nitrogen loss to groundwater, tracegas fluxes, evapotranspiration, water and nutrient use efficiencies, reproductive output, phenology, and changes in species composition of plants and animals. To explain the mechanisms by which species composition changes in whole-ecosystem experiments, supplementary experiments examining species interactions such as competition, disease, herbivory, and plant-microbe interactions may be necessary.
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From page 17... ...
An additional area of high priority is the development and validation of remote-sensing procedures to estimate productivity and soil processes on a regional scale. These measurements could provide validation for the substantial data on terrestrial carbon pools that are currently being synthesized, mapped and used in process models to predict global carbon fluxes.
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From page 18... ...
At present, the responses of trace-gas fluxes to simultaneous changes in these variables cannot be adequately predicted. For this reason, the major causes of the increases in atmospheric concentrations of biogenic trace gases are not known, and the isotopic budget of methane, a major trace gas, is severely out of balance given current estimates of sources and sinks (Cicerone and Oremland, 1988)
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From page 19... ...
inverse modeling, which links information from terrestrial ecosystems with global atmospheric budgets. Research Program The research program outlined here is discussed in greater detail in international documents (IGBP, 1990a, 1990b)
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The highest priority should be given to field manipulations and associated process-based modeling to test these hypotheses; and to inverse modeling, linking terrestrial sources and sinks to patterns of atmospheric changes in trace-gas concentrations. Field manipulation experiments and process-based models are essential to delineate controls over processes, which must be the basis of meaningful scenarios of future trace-gas flux.
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From page 21... ...
Moreover, the world's future ecosystems will experience novel combinations of environmental factors, an altered disturbance regime, and exploitation by a larger human population. Patterns and intensity of land and water management for food, fuel, and fiber are highly responsive to human demand as well as to climate, but the ecological impact of a given rate of population growth will differ dramatically between societies (Stern et al., 1992)
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From page 22... ...
Research Questions The major research questions in this section are: How can the future structure and distribution of terrestrial ecosystems be predicted as they change in response to global change? How will increasing CO2 and climatic change alter the rate and extent of disturbances to influence the interaction and distribution of currently widespread species and of general types (functional groups)
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From page 23... ...
Socioeconomic models that predict these changes should be validated with historical data and satellite observations of current trends and used to predict ecosystem structure, landscape structure, and dispersal of organisms. These efforts should be focused in areas where land-use changes (including altered management practices)
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These species-specific scenarios provide a basis for monitoring at community boundaries those parameters that would be the most sensitive indicators of biotic response to climatic change. In the case of crop species, the scenarios will provide critical information relevant to the sustainability of human populations.
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Priority should be given to synthesis and modeling focused on processes likely to cause large functional or structural changes in ecosystems. The following areas are particularly critical: • predicting the types and magnitude of human impact on terrestrial ecosystems; • determining the role of CO2 concentration and climate, as mediated by species interactions, in governing future distribution of currently widespread species and of generalized functional groups; and • understanding the role of landscape-scale processes, especially disturbance and land-use change, in governing ecosystem change.
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From page 26... ...
The other area of concern, the effects of ecological complexity (i.e., genetic diversity in populations, species diversity, landscape diversity) on ecosystem function, has received less attention.
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From page 27... ...
Research Questions Although it is well established that human activity is causing a loss of diversity within and among species as well as an increase in landscape diversity, there is little ability to predict the patterns and consequences of these changes. Several major questions arise: Are there predictable patterns of change in ecological diversity -- by level of diversity, functional or taxonomic group, or region?
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From page 28... ...
Such studies should emphasize those ecosystem functions that will alter terrestrial feedbacks to the atmosphere or interactions among landscape units, or cause further changes in ecological diversity. Particular attention should be paid to the impact of diversity within as well as between functional groups and to thresholds of diversity below which ecosystem function is seriously impaired.
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From page 29... ...
Observational studies can now take advantage of past human alterations of landscape diversity to examine what types of landscape units are most sensitive to changes in the size and arrangement of patch types within a landscape or barriers such as chains of rivers and lakes. Predictions of future patterns of landscape diversity will need to make use of socioeconomic models of human populations and land use, as well as the developing understanding of patch interactions on a landscape scale.
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From page 30... ...
At present however, how the current vegetation will partition water and energy under novel combinations of CO2, water, and nutrition cannot be predicted accurately, much less how future communities with different canopy structures would regulate water and energy flux. Under what conditions do physiological controls over stomatal conductance exert strong effects on canopy conductance (Jarvis and McNaughton, 1986; Rosenberg et al., 1989)
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From page 31... ...
How do changes in cropping patterns, decertification from overgrazing, land-use change, or wholesale species changes in unmanaged ecosystems affect the surface energy balance and the various components of the hydrologic cycle? The ecosystem questions are important because changes in surface energy and water balance may feed back to alter the rate of global change.
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From page 32... ...
Mechanistic distributed hydrologic models need to be developed or modified to predict the effects of changing canopy conductance, canopy architecture, and rooting patterns on evapotranspiration, runoff, soil water storage, snowpack, groundwater recharge, and the watershed supplies of surface water and groundwater, using data from watershed manipulations. Monitoring of streamflow in these watersheds should be continued because streamflow may be one of the more sensitive parameters of global change.
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From page 33... ...
Measurement of canopy conductance as a function of CO2, temperature, water supply, nutrients, and growth form is required before the current models can predict water budgets under future climatic scenarios. The highest priorities should be given to regional hydrologic modeling, development of remote-sensing methods to measure model inputs, and the field measurements needed to validate these models in order to link the relatively sophisticated current understanding of patch-scale water and energy balance (SVAT and GHM models)
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From page 34... ...
With global changes in the transfer of water and materials from land to aquatic systems, changes in species composition will probably occur, with as-yet-unknown consequences for ecosystem function. Certain fisheries are likely to expand (Magnuson et al., 1990)
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From page 35... ...
THE HYDROLOGIC CYCLE AND ECOSYSTEM FUNCTION. Objective: To determine how changes in the hydrologic cycle will alter productivity and biogeochemical cycling and transport in aquatic systems and associated riparian
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From page 36... ...
Information from Third World countries should be synthesized to determine the effect that harvest of freshwater and marine resources has on patterns of human land use and harvest of terrestrial and aquatic resources.
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From page 37... ...
Within 2 to 5 years a research plan that identifies the role of aquatic ecosystems in the global carbon cycle may be expected. Within 10 to 20 years our understanding should be sufficiently advanced to predict how global change will affect the flux of materials through aquatic systems to the ocean and the impacts these changed fluxes will have on the global carbon cycle, aquatic species composition, the productivity of fisheries, and the quality of water for drinking, industry, and agriculture, all of which affect the human carrying capacity of the earth.
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