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Improving Estimations of Past and Future Environmental Changes in the Western United States Using Stable Isotope and Plant Morphology Analyses: Peter Kent Van de Water

Project Title: Improving Estimations of Past and Future Environmental Changes in the Western United States Using Stable Isotope and Plant Morphology Analyses
Mendenhall Fellow: Peter Kent Van de Water, (541) 754-4495, pvandewater@usgs.gov
Duty Station: Corvallis, Oregon
Start Date: October 1, 2003
Education: Ph.D. (Geosciences), 1999, The University of Arizona
Research Advisors: Sarah L. Shafer, (541) 754-4498, sshafer@usgs.gov; Robert S. Thompson, (303) 236-5347, rthompson@usgs.gov; Steve Hostetler, (541) 737-8928, steve@usgs.gov

Project Description: Many studies designed to reconstruct past environments have assumed that the relationships between climate and individual plant species are relatively constant through time. Yet modern studies have shown that changing atmospheric carbon dioxide (CO2) concentrations can alter a plant’s physiological acquisition of carbon and its associated water-use efficiency. These physiological changes produce distinct signatures in the stable carbon and oxygen isotopic ratios within plant tissues, alter the micro-morphology of plant organs (such as the number and size of leaf stomates), and affect how a plant responds to changes in climate. This research project uses stable isotope and micro-morphological analyses of plant tissue to investigate both past and current interactions between plant species, climate, and atmospheric CO2 concentrations. For past time periods, analyses of plant macrofossils contained within packrat middens in the western United States allow us to track the relationships between vegetation and past changes in climate and atmospheric CO2 concentrations over the last 21,000 years and across wide spatial scales. For modern time periods, we are studying the interactions between vegetation, climate, and atmospheric CO2 by sampling vegetation along elevation transects in the western United States. These modern sampling transects focus on those plant species that are most abundant in the packrat midden fossil record. Together, the data gathered from these modern and paleo-vegetation studies will improve our ability to reconstruct paleoenvironments and will be used to develop better numerical model simulations of both past and future environmental change.

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