The U.S. Geological Survey (USGS) Geosciences and Environmental Change Science Center (GECSC, Denver, CO) is offering a funding opportunity to a CESU partner for research in developing new techniques and using existing techniques to enhance understanding of the longterm effects of changes in climate and other environmental factors on the distributions of plant species and ecosystems in arid and semiarid portions of the western United States. Three questions of major interest over the next decade are (1) What plants and ecosystems are vulnerable to potential future changes in climate and atmospheric chemistry, (2) What are the long term responses of plant species to a range of changes in climate and atmospheric chemistry, and (3) What combinations of climatic conditions that could have been associated with distributions of species/ecosystems during past climatic episodes (including episodes of cooler than present and warmer than present climate) and how it might relate to the future. This research and information will advance our understanding of atmospheric CO2 and possible global warming that will contribute to decision-making that protects the sustainability of the earths¿ ecosystems. Through this CESU agreement, the federal and state university partners will cooperate fully in development of a research program that will produce data of plant/climate realationships and plant fossils to be used in support of CO2 and other global change research. The cooperation of the USGS and its CESU partner brings a combination of expertise to address this objective that is greater than that possessed by either partner on its own.