P2C2:Collaborative Research: Rocky Mountain Ecohydrology During the Eemian Interglacial

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This award's goal is to assess controls on Rocky Mountain forest health during the Eemian-interglacial (beginning ~130,000 and ending ~ 115,000 years ago), the most recent period in Earth?s history when growing season temperatures exceeded those of today. Since the Eemian warming occurred in the context of pre-industrial partial carbon dioxide (pCO2) concentrations, the research aims to isolate the response of dominant tree species to growing season temperatures that are comparable to those predicted to be normal by AD 2100. The project takes advantage of recently recovered and well-preserved Eemian-age wood samples from Snowmass, Colorado available to this project through collaboration with the Denver Museum of Nature and Science. The Eemian wood samples provide a rare opportunity to explore how forests in the western U.S. have responded in the past to summer temperatures ~3-5°C higher than today?s. Boreal forests play a critical role in the global carbon cycle and provide important macrofaunal habitat and ecosystem services. The simultaneous and coupled influences of warming, changes in mountain hydrology (such as the timing of snowmelt) and elevated pCO2 that are predicted to occur over the next century have led to widely disparate projections on the response of this ecosystem to global change. The researchers will make sub-seasonally-resolved delta oxygen-18 and carbon-13 (d18O and d13C) isotopic measurements on modern and Eemian wood samples from species in the southern Rocky Mountains that were common during the Eemian and remain dominant today. These wood samples will be used to test how growing season length, water utilization (i.e., summer rain versus snowmelt) and Water Use Efficiency during the Eemian (i.e., warm temperatures and low pCO2) compare to today (i.e., "cool" temperatures and high pCO2). This analysis will provide clarity on whether recent changes in a plant?s Water Use Efficiency is a product of the CO2 fertilization effect or from coupled changes in CO2 and temperature. In addition to the isotope measurements, the researchers will generate nested (50 km resolution) isotope-enabled general circulation model (GCM) simulations under Eemian and modern forcings to provide climatic inputs for the ecohydrological and ecophysiological process models used to interpret the proxy data. The products of this research will be an assessment of how temperature-driven shifts in surface hydrology (snow and soil processes), atmospheric circulation (North American Monsoon extent and duration), and surface/leaf temperatures combine to improve or disintegrate forest health, including increases in large wildfires and rates of tree mortality in the western U.S.The project will support two early career scientists working at the intersection of paleoclimatology, ecology, and climate dynamics. The Chicago-based multi-institutional collaboration will facilitate undergraduate and graduate research opportunities in stable isotope geochemistry and climate modeling that are leveraged between institutions and are fundamental for twenty-first century scientific training. Additionally, there is a strong collaboration with the Denver Museum of Nature and Science for research and education.