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Summary of Recommended Research To reduce uncertainty about the response of terrestrial ecosystems to global changes in climate and land use, and the effect these terrestrial responses may have on global climate, the U.S. Global Change Research Program should address six major questions as its contribution to the International Geosphere-Biosphere Program: 1. What are the interactive effects of changes in COy climate, and bio- geochemistry on the terrestrial carbon cycle and on food and fiber production? Within 10 years a focused research program could determine (1) the magnitude and general location of those carbon emissions to the atmosphere that become sequestered in terrestrial ecosystems and (2) the extent and conditions under which elevated CO2 influences production. 2. What factors control trace-gas fluxes between terrestrial ecosystems and the atmosphere? Within 5 to 10 years an experimental research program could determine the major controls over fluxes of radiatively important trace gases from the terrestrial biosphere, yielding an explanation for current rapid increases in these gases in the atmosphere. 3. What are reasonable scenarios of the future distribution, structure, and productivity of both managed and unmanaged ecosystems based on changes in land use, disturbance regime, and climate? Two to 5 years should be adequate for development of a strong theoretical framework and understanding of the links between the natural and social sciences that are necessary to predict the future distribution and structure of terrestrial ecosystems. Within 10 to 20 years models that project future productivity and the role of terrestrial ecosystems in global
2 THE ROLE OF TERRESTRIAL ECOSYSTEMS IN GLOBAL CHANGE processes should be sufficiently realistic to serve as a strong basis for manage- ment decisions affecting the rate of global change. 4. How will global change alter biotic diversity and what are the ecosystem consequences? Within 2 to 5 years a theoretical framework and research plan could be developed through workshops that could, in the long term (10 to 20 years), explain the major ecosystem consequences of losses of biotic diversity and provide programs to maintain or restore the ecological functioning of damaged ecosystems. 5. How will global change affect biotic interactions with the hydrologic cycle and surface energy balance? Within 5 to 10 years models should be suffi- ciently realistic to describe how changes in the physiology and structure of veg- etation affect regional and global water balance and climate. 6. How will global change affect biotic controls over transport of water, nutrients, and materials from land to freshwater ecosystems and to coastal zones of the ocean? Within 2 to 5 years a research plan and theoretical framework can be expected that will identify the role of aquatic ecosystems in the global carbon cycle. Within 10 to 20 years our understanding should be sufficiently advanced to predict how global change will affect the flux of materials through aquatic sys- tems to the ocean and the impacts this will have on the global carbon cycle, aquatic species composition, and the productivity of fisheries that affect the human carry- ing capacity of the earth. Within each of these six major research topics, this report presents a general research program that prioritizes topics according to their potential to reduce un- certainty about the role that terrestrial ecosystems play in global change over time scales of decades to centuries. Three elements are highlighted for immediate action because they are key components of the terrestrial research program that are unlikely to proceed without focused attention: a. Experiments that determine ecosystem responses to interactions among elevated COy temperature, water, and nutrients. This program requires estab- lishment of large-scale expensive field experiments in selected managed and unmanaged ecosystems to determine how the response of entire ecosystems to elevated CO2 is constrained by temperature, water, and nutrients. The experi- ments required are well defined so that an experimental program can be imple- mented immediately. These are the most critical experiments required to improve our understanding of the response of terrestrial ecosystems to climate change and of the feedbacks to climate. Because of the expense and magnitude of these ex- periments, they cannot be implemented without focused attention. b. Research to predict the role of landscape-scale processes, especially dis- turbance and land-use change, in governing the future structure and distribu- tion of ecosystems. Because the socioeconomic and ecological disciplines re- quired to accomplish this task are not well integrated, work should begin with
SUMMARY OF RECOMMENDED RESEARCH 3 interdisciplinary workshops to define the major uncertainties and research re- quired to establish a strong theoretical framework. In the coming decades, human alterations of land use and disturbance regimes will have the largest impact on the terrestrial biosphere. Without explicit study of this phenomenon, the conse- quences of these changes for the earth system cannot be predicted, nor can in- formed policy decisions be made that would modify this human impact. c. Research to determine how changes in species composition (e.g., inva- sion or extirpation of species or functional groups with strong ecosystem im- pacts) affect the functions of managed and unmanaged ecosystems. This activ- ity should also begin by synthesizing existing information and convening workshops to develop research approaches. This program is critical because habi- tat destruction, human introductions of exotic species, and rapid climate change are causing rapid changes in species composition and loss of species diversity. Yet, these changes cannot be predicted, and little is known about their ecological consequences.
