Effects of interannual climate variation on aboveground phytomass in alpine vegetation

Relationships between peak annual vascular aboveground phytomass and annual climate variation in alpine plant communities located on Niwot Ridge, Colorado, were analyzed using path analysis. The five community types, fellfield, dry meadow, moist meadow, wet meadow, and snowbed, represent a snow depth-soil moisture gradient and broadly represent the most common vegetation types on east-facing slopes of the Front Range alpine zone. Using nine successive years of data, this is the first longer term analysis of alpine phytomass and climate and one of the longest nonagricultural production records available. Live phytomass ranged from 97 g/m^2 (snowbed) to 237 g/m^2 (fellfield). Among-community differences in phytomass were greater than differences among years, but there was also significant phytomass variation among years. Path analysis indicated that climate accounted for 15-40% of the variation in phytomass. The dry communities, fellfield (exposed rocky summit areas dominated by cushion and mat plants) and dry meadow, were most sensitive to previous year precipitation, the moist and wet meadow communities were most sensitive to current growth season soil moisture, and the snowbed community was most sensitive to date of snow release. Because of the relatively high amount of variation attributable to variables related to precipitation, changes in precipitation regimes that may occur in alpine ecosystems will likely result in changes in phytomass that are detectable with clip-harvest methods.