Drs. Dean and Graybill will continue their dendroclimatological work to reconstruct past climates in the United States Southwest. Because the size and configuration of annual growth rings in trees are affected by changes in rainfall and other environmental variables, it is possible to use them to reconstruct past climatic change. Also, since tree rings are deposited on an annual basis, they permit an accurate dating of this change. Drs. Dean and Graybill will add to an already substantial data base through the analysis of additional cores from living trees in Arizona, New Mexico, Utah, and Colorado. Their preliminary work show a major climatic peturbation at approximately 1300 AD; this corresponds to a time of major cultural change in the Southwest. The Arizona team will focus their attention on this issue. They will reconstruct changing annual and seasonal variations in precipitation, temperature, growing season length, the Palmer Drought Severity Index, and changes in stream flow. The Southwestern United States saw the rise, in pre Hispanic times, of complex cultures which covered large portions of several states. These archaeological complexes expanded and contracted over time and the largest disintegrated before the arrival of the Spanish. Archaeologists have hypothesized that these cultural changes were in fact responses to variation in the environment and that the Southwest offers an excellent change and human response. The tree ring data will significantly aid in analyses of this kind. This research will be important not only for archaeologists, but also paleoecologists and scientists interested in climate dynamics and changes. Changes in temperature and precipitation which are of such concern today occurred many times in the past. It is important both to understand them and to learn how human societies responded.
