Final Report for RWO 81 Rocky Mountain Ungulates
Quaking aspen is a widespread tree that is in decline across wide areas of western North America, and is predicted to experience a large range shift if future climate predictions are realized. The purpose of our study was to determine what climate factors have influenced aspen growth in Yellowstone National Park, USA, and to determine whether these climatic influences vary across a heterogeneous landscape. We extracted increment cores from 10-12 aspen in each of 16 stands spread across a 1,526 km2 area. Using ring widths, we created a182-year standardized chronology from 1821 to 2003 A.D. composed of 151 series. We then assessed correlations of growth using instrumental records of temperature, precipitation, and the Palmer Drought Severity Index (PDSI) from 1932 to 2002, and records of maximum snow depth from 1949 to 2002. We found positive relationships between growth and springtime maximum snow depth, and negative relationships between growth and temperature and moisture stress (PDSI). Aspen were impacted by these factors from the previous growing season, suggesting a lag effect of climate. Variation in sensitivity to temperature and PDSI among our stands could not be explained by landscape variables, but sensitivity to the prior March maximum snow depth was greater at high elevations and on shallower slopes. High snow depth probably produces a long- lived water source at the beginning of the growing season. Our study demonstrates that aspen respond to variation in moisture related factors, and that changes in aspen growth due to future climate shifts will vary across small scales.
Jules Erik S., Carroll Allyson L. & Kauffman Matthew J. 2010. Relationship of climate growth of quaking aspen (populus tremuloides) in yellowstone national park. Manuscript submitted for publication. Department of Biological Studies, Humboldt State University: Arcata, California.