Biotic responses to climatic change or human manipulation are inherently complex because of wide differences in organism sensitivities and response times, the influence of history and scale, and the various interactions between organisms and with the physical system. In arid and semi-arid lands, which cover about 12.5 percent of the Earth's land surface, the effects of climatic variability on vegetation are greatly magnified, particularly because most plants exist near their physiological limits. How arid land vegetation might in turn affect climate is uncertain, though there is some indication that decreasing cover and increasing albedo could promote regional drought. Whether in response to projected Greenhouse climates or intensified land use, vegetation in such critical watersheds as the Rio Grande and Colorado River basins is apt to change in the near future. There is a need to understand the direction and rate of this change and how it might affect water use and availability in the region. The objectives of this project are to achieve a dynamic understanding of vegetation change and its relation to water resources, to develop such an understanding in a manner appropriate to the hierarchy of spatial and temporal scales implicit in a study of global change, and to determine whether the responses of dryland vegetation to global change are predictable from past and present behavior of vegetation. For additional information, see the home page for the Desert Laboratory, which is operated jointly by the University of Arizona's Department of Geosciences, Department of Ecology and Evolutionary Biology, and the U.S. Geological Survey.
