EFFECTS OF INTERANNUAL CLIMATE VARIATION ON ABOVEGROUND PHYTOMASS IN ALPINE VEGETATION

Relationships between peak annual vascular aboveground phytomass and a nnual climate variation in alpine plant communities located on Niwot R idge, Colorado, were analyzed using path analysis. The live community types, fellfield, dry meadow, moist meadow, wet meadow, and snowbed, r epresent 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 l onger term analysis of alpine phytomass and climate and one of the lon gest nonagricultural production records available. Live phytomass rang ed from 97 g/m(2) (snowbed) to 237 g/m(2) (fellfield). Among-community differences in phytomass were greater than differences among years, b ut there was also significant phytomass variation among years. Path an alysis 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 sensit ive to previous year precipitation, the moist and wet meadow communiti es were most sensitive to current growing season soil moisture, and th e snowbed community was most sensitive to date of snow release. Becaus e of the relatively high amount of variation attributable to variables related to precipitation, changes in precipitation regimes that may o ccur in alpine ecosystems will likely result in changes in phytomass t hat are detectable with clip-harvest methods. Key words: alpine tundra ; climate change; Colorado; ecosystems; path analysis; phytomass; plan t community; soil moisture.