Tuesday, August 8, 5:00-6:30 pm
Poster Session 11 - Plant physiological ecology
Exhibit Hall, Ballroom Level, Cook Convention Center

Spatiotemporal response of transpiration to climate variation in a snow dominated mountain ecosystem.

Christensen, Lindsey *,1, Tague, Christina 2, Baron, Jill 1, 3, 1 Natural Resource Ecology Laboratory, Fort Collins, CO, U.S.A.2 Department of Geography, San Diego, CA, U.S.A.3 US Geological Survey, Fort Collins, CO, U.S.A.

ABSTRACT- Total water transpired annually in western slope Sierra Nevada mountains is highly responsive to climatic variability. We used the RHESSys model to assess elevational differences in the sensitivity of transpiration rates to climate across the Upper Merced River in Yosemite National Park, CA. At the basin scale, model predictions show annual water transpired was lowest in driest and wettest years, and greatest in years of moderate precipitation. At finer spatial scales, distinct differences in responsiveness of transpiration rates to climate occurred along an elevational gradient. Low elevations showed little interannual variation in transpiration amounts due to topographically controlled high soil moistures along the river corridor. Our simulations showed transpiration was most responsive to variations in precipitation (both annual total and maximum snow depth) and temperature in middle elevations, but effects of these drivers varied with elevation. Forest stand transpiration amounts between 1800 and 2350 m responded more strongly to precipitation: the highest amount of transpiration occurred during wet and high snow years regardless of annual temperatures, while the lowest amount of transpiration occurred in warm and dry years. At elevations between 2350-3000 m, temperature was the most important climate influence on transpiration. Maximum transpiration occurred in warmest years regardless of precipitation variability. Consistent precipitation as snow at this elevation range provides enough moisture for growth, and elevated temperatures influence transpiration both directly as a control on physiologic responses such as stomatal conductance and indirectly through its relationship with atmospheric vapor pressure deficit. Transpiration rates varied little from year to year at highest elevations because of continuous seasonal snowpacks. Because temperature and annual precipitation do not vary linearly, peak transpiration rates occurred in years with moderate precipitation. Elevational differences in vegetation water use and sensitivity to climate are significant and will likely play a key role in controlling the responses and vulnerability of Sierra ecosystems to future climate change.

Key words: mountain ecosystems, hydrological processes, RHESSys

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