Doctoral Dissertation Research: Holocene Climatic and Ecologic History of the Northern Great Basin

University Of Oregon Eugene, Eugene OR

Investigators

Abstract

The objectives of this doctoral dissertation research project are to reconstruct the climate, vegetation, and fire history in the northern Great Basin from an examination of fossil pollen and charcoal records contained in lake-sediment cores. The Great Basin is a region of diverse topography, vegetation, and climate, and as such it provides an excellent opportunity to study the response of ecosystems to a wide array of environmental changes in the past. By focusing on three lake sites at different elevations, this study will (1) elucidate the response of vegetation and fire regimes to changes in effective moisture, temperature, and other bioclimatic variables; (2) reconstruct the biogeographic history of important conifer species growing at different elevations; and (3) apply modern pollen-climate relations in western North America to identify the magnitude of past climate and vegetation changes. Past changes in vegetation will be determined by changes in the relative and absolute abundances of pollen types in stratigraphic records. The presence of plant macrofossils in the cores will help confirm species identifications in cases where the pollen cannot. Variations in past fire activity will be inferred from changes in the rates of macroscopic charcoal accumulation in contiguous samples. Interpretation of the fossil pollen data in terms of past climate and vegetation will be based on the quantitative relationship between modern pollen data and present-day climate information. The chronology of environmental changes will be developed from a series of radiocarbon dates and lead-210 dates, as well as the age of known tephra layers. The products of this study will be a better understanding of Holocene forest development at different elevations in the northern Great Basin, and information on the role of fire and climate in the ecological history. The results of this research will contribute to a better understanding of (1) the effects of global climate change, past and present, on regional vegetation patterns and fire regimes in the Great Basin; (2) modern pollen-climate relations and their use in the reconstruction of past climates; and (3) the environmental controls on human activities in the northern Great Basin during the Holocene. Since 1988, the western U.S. has experienced a number of large, stand-replacing fires. In the year 2000 over 8 million acres burned in the U.S., and in the first six months of 2002 there have been ~2.5 million acres consumed by wildland fires. Many of these fires may be attributable to anomalously dry conditions throughout the west. Heightened fire activity is predicted in models of future climate change, and the best analogue for these conditions may be past periods when the climate was warmer- and drier-than-present. By understanding the linkages between climate, vegetation, and fire in the past, recent fire events can be placed within a context of natural variations occurring on decadal-to-millennial time scales. Information on the natural range of variability will help land-use managers in the United States develop strategies that consider forest sensitivity to climate change and disturbance regimes. The use of modern pollen and climate analogues will improve our ability to reconstruct past climate conditions from fossil pollen records. Pollen data are the primary terrestrial database used to reconstruct past climate, so this refinement is an important contribution to paleoclimatology and geography. Finally, this study will contribute to archeology by providing an environmental backdrop for cultural changes in the Great Basin. Periods of drought, for example, seem to be associated with changes in subsistence patterns in this region. This research will help to clarify these relationships. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.