Toward an Understanding of Global Change Initial Priorities for U.S. Contributions to the International Geosphere - Biosphere Program (1988) / Chapter Skim
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Ecological Systems and Dynamics
Ecological Systems and Dynamics
Pages 69-106
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From page 69... ...
O What ecological processes and mechanisms require further understanding, and what data sets are essential to model biotic responses to global change? · What are the temporal en cl spatial dynamics in the responses of ecological systems to global change?
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From page 70... ...
The marine biotic community is also complex and highly variable, frequently clemonstrating situations where the effects are removed in time and space from the events that caused them (Rothschild, 1986, 1988~. These examples caution against efforts to predict biotic responses, for example, by simply correlating biological phenomena with the spatial distribution of climate or by using single-factor causation theories.
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From page 71... ...
As a result, there would be lags decades in length in the adjustment of ecological systems to rapidly changing climatic conditions. These lags in the match between climate and vegetation will become apparent in the mid-continent Tong before doubling of carbon dioxi(le has occurred.
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From page 72... ...
. Ecophysiological responses to stress and the ability of plants and animals to reproduce and establish themselves ultimately determine the geographical range limits of individual species.
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~3 1~ , ~ .' 0 400km I 1 ~ 1 I ~ ~ ~ ~ 1 -__., >A ~( \\ ~ an\ I .
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From page 74... ...
The resulting new combinations of vegetation, climate, and soils can result in altered spatial patterns of such fundamental processes as net primary production (Pastor and Post, 1988~. More subtle, but still important, processes such as evolved host-pathogen relationships may also be disrupted by the stress of new conditions, resulting in increased frequency of epidemics (Leonard and Fry, 1986~.
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From page 75... ...
There are examples where ecosystem function appears to be relatively independent of species composition (Schindler, 1988~. There are also examples where changes in species have had remarkable alterations in ecosystem processes, for example, the alterations produced by key predators such as the starfish Pisaster in the rocky intertidal (Paine, 1966)
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From page 76... ...
Thus the influence of species composition on ecosystem properties becomes a critical issue. Climate change wiB also have direct effects on ecosystem processes and gas exchange with the atmosphere.
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From page 77... ...
Also, our knowledge of plankton distributions in the past is based on data for the few taxa, such as the foram~nifera, that have easily preserved hard parts. Because the ecological role of these protozoans is not wed known, it is difficult to predict the degree to which changes in their species composition indicates a change in the plankton community in general.
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From page 78... ...
Diatoms are the preferred food of many organisms in the food webs of commercially exploited fishes, and when replaced by other types of phytoplankton the dinoflagelIates, for example, in the case of the Peru Current—the yield of the fish of greatest economic interest is reduced dramatically (Barber and Chavez, 1983~. There is some evidence that at least some economically important seaweeds may be quite sensitive to increases in water temperature.
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From page 79... ...
Removal of vegetative cover, as well, decreases net primary production and net ecosystem production, and fluxes of water to the atmosphere through evapotranspiration. Deforestation dramatically increases sediment and dust production, runoff, and solute concentrations, with consequences for biota in lakes, estuaries, and coastal zones (Bormann and Likens, 1979~.
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From page 80... ...
This predictive process will require the combined initiative of biologists, demographers, development economists, and agricultural experts. Changes in Carbon Dioxide The primary effects of increased carbon dioxide concentration are increased photosynthetic rates and decreased stomata!
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From page 81... ...
The resulting community structure is influenced by other environmental factors such as moisture, light, nutrients, an(1 temperature (Bazzaz et al., 1985~. It is important to note that the response at the community level may not be directly predictable from the response of individual species to elevated CO2 or to other environmental factors because of changes in species composition and interactions with heterotrophic organisms.
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From page 82... ...
Because such experiments cannot be performed for each potentially important factor or interaction, the proper approach wiD be to carefully integrate laboratory and field experiments with simulation models, and with small-scale studies aimed at particular organisms or interactions. Innovative indices of responses to pollutants are needed for both survey work and retrospective studies.
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From page 83... ...
Methodologies for extrapolation from experiments and measured sites to global scales require more development. Sea Level Change The effects of the expected rate of sea level rise in the next century, nearly 1 cm/yr, may be somewhat analogous to the effects of sea level rise that occurred at the end of the last ice age, 80 m over an interval of 14,000 years (Bloom, 1988~.
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From page 84... ...
Consequently, sea level rise in the next century is likely to drown many if not ah salt marsh systems except in areas where the land is rising and reducing the rate of relative sea level change. Tidal marshes are important habitats because they are highly productive.
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From page 85... ...
ecosystem response to global environmental change. This is in part because rates of element cycling may change more rapidly than species composition (days to years versus years to centuries)
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From page 86... ...
structures will be required for this linkage. A number of ecological research teams are developing "generic ecosystem models" to investigate and contrast the likely responses of different terrestrial ecosystems to changes in the global environment over the next century.
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From page 87... ...
The predictions are based on a population-based model that simulates forest growth, combined with a processfunctional model that simulates soil moisture and nutrient cycling. Climatic inputs were the same for the two runs, but (a)
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From page 88... ...
For example, Tow availability of nitrogen, the most frequently limiting nutrient in terrestrial ecosystems (Pastor et al., 1984) , may prevent ecosystems from changing in response to changing climate until after temperature thresholds are exceeded for dominant species.
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From page 89... ...
Soil moisture influences vegetation physiognomy, which in turn influences albedo and surface roughness (Dickinson, 1986~. Sediment loadings, types of particulate and soluble inputs, and flow rates can affect downstream terrestrial ecosystems and turnover rates, flow, and current dynamics in water bodies.
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From page 90... ...
Appropriate atmospheric models are now needed to simulate aeolian pathways. In a related set of ecological processes, changes in climatic patterns will affect the distribution and/or intensity of fire, which is a major source of release of elements from terrestrial systems to the atmosphere.
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From page 91... ...
As sea level rises, the ability of wetland plants to oxidize their rhizospheres
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From page 92... ...
Inputs of both nutrients and pollutants to estuaries and coastal seas could change as climate affects rates of erosion and leakage of substances from terrestrial ecosystems. Primary production in many estuaries and coastal regions is limited by nitrogen (McCarthy, 1980)
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, the desert-grassTand transition (which is undergoing (lirect human impact as well as being sensitive to climatic changes) ; and estuaries (areas of economic importance at the focal point of pollutant stress)
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From page 94... ...
Because each system varies in its dynamics, variables to be studiec3 will be different in each system. For example, in some systems the variable of interest is the influence of physical factors on net primary production, and in others, it might be sedimentation and gas exchange, how the food web partitions primary pro(luction, or how predators high on the food chain feed back on production.
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From page 95... ...
Two strategies are being adopted by the Global Ocean Flux Study to make long time-series observations in oceanic regions that provide important steps in this direction. The first involves the use of satellite observations for ocean color that serve as a proxy for near-surface phytoplankton biomass.
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From page 96... ...
Ongoing programs relevant to the above include the World Ocean Circulation Experiment, Global Ocean Flux Study, Global Ecosystem Dynamics, and the U.S. National Science Foundation's Longterm Ecological Research network.
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From page 97... ...
For example, regions of subsidence can be used to simulate the effects of sea level changes on tidal marshes or intertidal communities. In shelf areas, fish harvests alter the abundances of species, providing opportunities to study community structure.
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From page 98... ...
Because of this, longterm models of ecological response to global environmental change must represent both process-functional and population-community aspects of ecosystems. Certain species play critical roles in ecosystems; if change is so rapid that these populations are killed outright, drastically changed or eliminated processes such as primary production, decomposition, and nutrient cycling wiD also respond.
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From page 99... ...
Couple the whole-plant function mode! with population-community and ecosystem models to simulate ecosystem processes as affected by population change.
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From page 100... ...
1988. The exponential shape of late glacial sea level change.
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From page 101... ...
1986. Response of mammalian communities to environmental changes during the late Quaternary.
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From page 102... ...
Report of the Working Group on Terrestrial Ecosystems and Atmospheric Interactions, ICSU Ad Hoc Planning Group on Global Change. Jacobson, G
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1987. Exchange of materials between terrestrial ecosystems and the atmosphere.
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From page 104... ...
Pp. 6~94 in Physiological Ecology of North American Plant Communities, B
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From page 105... ...
1985. Direct Effects of Increasing Carbon Dioxide on Vegetation.
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From page 106... ...
Clark, Harvard University Robert E Dickinson, National Center for Atmospheric Research John Edmoncis, Massachusetts Institute of Technology Robert Howarth, Cornell University John Imbrie, Brown University Jane Lubchenco, Oregon State University James J
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