Phenology


Plant activity is governed by two parameters: temperature and soil moisture availability. Cold winter temperatures limit growth activity between November and March (Caldwell 1985, Comstock and Ehleringer 1992). While a limited number of species, such as the early spring ephemeral Ranunculus testiculatus (bur buttercup), may begin activity during warm periods in February, most annuals do not begin growth until the warm periods between snowstorms in early March. At lower elevations, a number of herbaceous perennials such as Balsamorhiza macrophylla (cutleaf balsamroot) may begin to leaf out during March, but most woody perennials do not leaf out until mid- to late April. The annuals and most herbaceous species at lower elevations have completed growth and reproduction by mid-June and then remain dormant until the following autumn or spring (Smedley et al. 1991). In contrast, woody species at lower elevations remain active from April through October, although the vast majority of the growth will occur during the spring (Donovan and Ehleringer 1991). At higher elevations, vegetative and reproductive growth are delayed until late May or June by cold temperatures. Plants at higher elevations will remain active throughout the summer, even though there may be little summer precipitation (Dina 1970, Dina and Klikoff 1973).