COS 31-2 - Reduced snowpack and passive warming effects on montane meadow plant growth, phenology, floral productivity, and nectar characteristics

Abstract: Climate change may have some of the most dramatic effects in montane species for which snowmelt is a phenological trigger. For plants in these systems, a relatively small amount of warming could potentially enhance vegetative growth and trigger earlier phenology. We used experimental manipulations of snow removal and warming in a high-elevation meadow from 2010-2019 to evaluate phenology, growth, foliar frost responses, flower production, nectar concentration, and nectar volume of two species of perennial forbs. We hypothesized that 1) warming and snow removal would trigger earlier phenology, but we did not know whether one variable or the interaction of variables would be stronger drivers, 2) warming would produce lower nectar volumes but similar sugar concentrations compared to control plots and 3) the effects of each treatment on flowering onset, flowering duration, and maximum floral display would strengthen over time. We examined arrowleaf balsamroot (Balsamorhiza sagittata) an early-emerging flowering species and sulphur flower buckwheat (Eriogonum umbellatum), a late-season flowering species. Both are key forbs for pollinator communities and are widely distributed and locally abundant in western North America. We found that snow removal advanced green-up in both species and led to advanced flowering in some years. Snow removal increased the height of later blooming E. umbellatum, but led to increases in frost damage to flowers of earlier blooming B. sagittata. Warming had no effects on E. umbellatum, but increased heights of B. sagittata and led to reductions in frost damage to flowers. For a subset of these years (2015-2016), we were able to examine the effects of warming on nectar concentration and volume, and found that warming reduced the nectar volume and increased nectar sugar concentration in both species in both years. We were able to examine longer-term effects of the treatments on B. sagittata from 2013-2019. The combination of warming with snow removal led to earlier flower onset, extended flowering duration, and increased maximum floral display. The effect of warming with snow removal on earlier onset and maximum floral display strengthened over time. Combined, these results suggest that climatic warming and reduced snowpack could lead to 1) earlier phenology in both species, 2) changes in the volume and concentration of nectar resources provided to local pollinators by both species, and 3) higher overall floral production in B. sagittata. These changes could have important bottom-up impacts on ecosystem functioning with changing climate.