Effects of experimentally reduced snowpack and passive warming on montane meadow plant phenology and floral resources.

Abstract

Climate change can have a broad range of effects on ecosystems and organisms, and early responses may include shifts in vegetation phenology and productivity that may not coincide with the energetics and forage timing of higher trophic levels. We evaluated phenology, annual height growth, and foliar frost responses of forbs to a factorial experiment of snow removal (SR) and warming in a high-elevation meadow over two years in the Rocky Mountains, United States. Species included arrowleaf balsamroot (Balsamorhiza sagittata, early-season emergence and flowering) and buckwheat (Eriogonum umbellatum, semi-woody and late-season flowering), key forbs for pollinator and nectar-using animal communities that are widely distributed and locally abundant in western North America. Snow removal exerted stronger effects than did warming, and advanced phenology differently for each species. Specifically, SR advanced green-up by a few days for B. sagittata to >2 wk in E. umbellatum, and led to 5- to 11-d advances in flowering of B. sagittata in one year and advances in bud break in 3 of 4 species/yr combinations. Snow removal increased height of E. umbellatum appreciably (~5 cm added to ~22.8 cm in control), but led to substantial increases in frost damage to flowers of B. sagittata. Whereas warming had no effects on E. umbellatum, it increased heights of B. sagittata by >6 cm (compared to 30.7 cm in control plots) and moreover led to appreciable reductions in frost damage to flowers. These data suggest that timing of snowmelt, which is highly variable from year to year but is advancing in recent decades, has a greater impact on these critical phenological, growth, and floral survival traits and floral/nectar resources than warming per se, although warming mitigated early effects of SR on frost kill of flowers. Given the short growing season of these species, the shifts could cause uncoupling in nectar availability and timing of foraging.