Abstract

Surveys of herbaceous flora found in flower in the eastern central Sierra Nevada (Nevada, USA) demonstrated the influence of climate variability on herbaceous phenology and observed species richness.  Mid-summer surveys conducted in two climatically different years showed differences in number of flowering species (greater in the wetter year) and their characteristic phenological class (more early vs. late-flowering species in the wetter year).  Between-year variation in phenology and species richness appeared to be keyed to snowpack duration, spring and summer moisture availability, and early growing season temperatures.  Responses in mesic habitats were greater than in xeric sites.   Phenological responses to climate variability can be interpreted in terms of displacement, compression, and amplification of the phenological cycle.  Comparison of the two surveys suggests that both displacement and amplification generated observed differences, with, in the wetter year, late snowpack and lower spring temperatures delaying flowering times and improved spring and early summer moisture conditions resulting in greater observed species richness.   Sensitivity of herbaceous species in these montane habitats to year-to-year differences in climate highlights the importance of considering effects of climate variability on phenology and population dynamics in short-duration plant biodiversity surveys and long-term monitoring programs.

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