Precipitation in alpine and subalpine ecosystems is variable from year to year and exerts a strong influence on ecosystem properties. Annual precipitation is dominated by winter snowfall, making the growing season short and soil moisture levels partially dependent on spring snowmelt. Primary production in these ecosystems is predicted to be highly vulnerable to variations in precipitation, especially changes in seasonality. To begin exploring this issue, I collected samples of aboveground biomass and plant community structure from alpine and subalpine sites throughout Colorado in 2007.  Sites were chosen to represent a broad gradient of seasonal precipitation patterns.
Results/Conclusions

Across all sites, aboveground biomass decreased significantly with increasing winter precipitation. This response is hypothesized to be due to differences in growing season length, although the interaction of soil moisture and growing season length is difficult to separate. Growing season length is influenced primarily by winter precipitation, whereas soil moisture is determined by an interaction of snowmelt and summer precipitation.  I outline an hypothesis for how changes in seasonal patterns influence primary production, by an interaction between growing season length and soil moisture constraints. I then explain an experiment being conducted to test this hypothesis.