Plant, community, and ecosystem responses to long-term snow depth forcing.
Loik, Michael*,1, 1 University of California, Santa Cruz, CA, USA
ABSTRACT- Uncertainty limits the utility of General Circulation Models (GCMs) for diversity management and ecological restoration in the face of climate change. Patterns of future precipitation for the arid and semi-arid regions of the western United States are highly uncertain, as some GCMs envision increased winter snowfall, whereas others anticipate reduced snowfall. Short-term shifts in ecological phenomena have been demonstrated in many global change experiments, yet little is known about the potential impacts of decadal increases or decreases in seasonal precipitation on ecological patterns and processes. This research evaluates the question: For semi-arid shrub land ecosystems, how have long-term, simultaneous increases and decreases in snow depth affected community patterns and ecosystem processes? This research utilizes fifteen 50-year-old roadside snow fences that span a 50 km transect as the source of long-term manipulations of snow depth. The study site is the Sagebrush – Bitterbrush shrub community of eastern California, for which the annual water budget is based primarily on winter snowfall. Results show that snow fences increase snow depth in "+snow plots" (by about 80% compared to upwind, ambient snow depth plots), and decrease snow depth (by about 20%) further downwind ("-snow plots"). Soil water content during the melt period was greater in +snow compared to -snow and ambient-depth plots. Species richness was highest in +snow plots, but overall canopy cover was not different among the three treatments. There was a shift from co-dominance by Artemisia tridentata and Purshia tridentata on ambient and +snow plots, to dominance by P. tridentata on -snow plots. In this regard, mortality of A. tridentata was highest on -snow plots, but there was no difference in mortality for P. tridentata. Plant water potential and photosynthesis were significantly higher in +snow compared to -snow and ambient-depth plots. There was greater litter and soil carbon at 10 cm depth in +snow and -snow plots compared to ambient-depth plots, but no effects on soil nitrogen. Overall, changes in plant community composition and ecosystem processes are consistent with altered patterns of snow depth, soil water content, plant production, recruitment, and mortality.
Key words: precipitation, Great Basin Desert, Artemisia tridentata, Purshia tridentata
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