EFFECTS OF INTERANNUAL CLIMATE VARIATION ON PHENOLOGY AND GROWTH OF 2ALPINE FORBS

Variations in growth, flowering, and phenology of two forbs, Acomastyl is rossii and Bistorta bistortoides, were compared among six years (19 83-1988) and five plant communities (fellfield, dry meadow, moist mead ow, wet meadow, snowbed) at an alpine site in the Front Range of Color ado. The purpose was to determine the extent to which the phenological patterns of these species Varied among plant communities acid how int erannual climate variability affects phenology and growth. There were significant differences in growth among communities for both species. In B. bistortoides, there were also significant differences among year s, due primarily to the influence of a single year (1983) when leaf le ngth increased by approximate to 10% and the average number of B. bist ortoides leaves nearly doubled. Key phenological events of both specie s (initiation of growth, date of maximum leaf length, leaf number, and flower number) were related to snowmelt patterns, resulting in differ ences among communities. There were also significant differences among years, again primarily related to the single year 1983, the year of a major El Nino Southern Oscillation (ENSO) event that produced high sn owfall amounts at the site. The increased leaf length in a high snow y ear is counterintuitive to the commonly accepted notion that alpine sp ecies may be limited by season length. We hypothesize that changes in phenology related to changes in snowfall or snowmelt will cause detect able changes in growth, but that these will not be predicted simply fr om phenology alone. Rather, the timing of snowmelt in relation to nutr ient availability, soil moisture, and air temperature will be critical in determining how individual species respond.