Integrating multiple temporal scales of snowfall, soil, and plant processes at the Great Basin Desert – Sierra Nevada ecotone

Background/Question/Methods

Snowfall is the dominant hydrologic input for high elevations and latitudes of the arid- and semi-arid western United States.  Many climate models envision changes in California’s Sierra Nevada snow pack characteristics, which would severely impact the storage and release of water for one of the world’s largest economies.  Climate change threatens the sustainability of this water supply through altered snowfall timing, reduced snowpack depth, changes in snow water equivalents, earlier snowmelt, and highly-uncertain but plausible scenarios of rain-on-snow events.  Climate model scenarios envision reduced snow pack and earlier melt under a warmer climate, but how will these changes affect soil and plant water relations and ecosystem processes, such as carbon storage?  To address this question, experiments utilize large-scale, long-term snow fences to manipulate snow depth and melt timing at a desert-montane ecotone in eastern California, USA.  A combination of instantaneous gas exchange and water potential measurements, plant community surveys, annual ring growth increments, in situ instrumentation, and long-term snow course data were used to couple physical and biological processes at daily, monthly, annual, and decadal scales.

Results/Conclusions

At this site, long-term April 1 snow pack depth averages 1344 mm (1928-2011) with a CV of 48%. Snow fences increased equilibrium drift snow depth by 100%. Soil moisture pulses were shorter in duration and lower in magnitude in low- than medium- or high-snowfall years. Evapotranspiration (ET) in this arid location accounted for about 37 mol m^-2 d^-1 of water loss from the snow pack between January 1 and May 1; sublimation was 10% of ET for the same period. Despite considerable interannual variation in snow depth and total precipitation, plant water potential stayed relatively constant over eight consecutive years, but photosynthesis was highly variable. At the decadal scale of the snow fences, changes in snow depth and melt timing have impacted growth of only three plant species. Moreover, annual ring growth increments of the conifers Pinus jeffreyi and P. contorta were not equally sensitive to snow depth. Results indicate complex interactions between snow depth, soil water, and plant characteristics at multiple temporal scales, which help drive the resilience of plant processes to large interannual variations in annual snowfall and manipulated snow depth. This resilience suggests that this ecotone may be stable in the face of anticipated changes in snow depth due to anthropogenic climate forcing.