Forest Succession and Climate Change: Coupling Land-Surface Processes and Ecological Dynamics.
Growing evidence supports the hypothesis that humans are in the process of inadvertently modifying the Earth's climate by increasing the atmospheric concentrations of carbon dioxide and other radiatively active trace gases. The present man-induced climatic change, often referred to as the "greenhouse effect", is different from natural changes because of its unprecedented pace and our incomplete knowledge of its consequences. As some scientists put it, humanity is performing on itself a "global experiment" which may entail a number of surprises. The potential changes in the behavior of atmosphere/biosphere interactions are of particular importance. Such changes could affect atmospheric dynamics, the local and regional hydrology, the global biogeochemistry, and, therefore, human societies. In the present thesis, five distinct aspects of climate/vegetation interactions are examined. First, the climatically and physiologically mediated impacts of increases in the concentration of carbon dioxide on the evaporation from agricultural crops, grassland, and forests are investigated using the Penman-Monteith combination equation. Second, the degree of coupling between the vegetation and the atmosphere, as defined by Jarvis and McNaughton, is reexamined taking radiative losses from the vegetation to the atmosphere into account. Third, the effects of changes in the mean vs. the variance of climatic variables are investigated using a modified version of the forest dynamics model developed by Pastor and Post, LINK-AGES. Fourth, using the same model, changes in the production of non -methane hydrocarbons are estimated as climate and/or vegetation change. Finally, the main part of the thesis focuses on the response of forests to climatic changes using a model treating the physics of energy and water exchange in detail. Because the Energy, water, and momentum eXchange, and Ecological dynamics model (EXE), couples the land-surface processes and the ecological dynamics of forests of northeast America, new insights are gained into the behavior of forests, in general, and the possible consequences of a greenhouse effect on forest hydrology and vegetation succession, in particular.
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- Physics: Atmospheric Science; Biology: Ecology; Hydrology