Earlier snowmelt accompanied by warmer soil temperatures in mid-latitude aspen forest and subalpine meadow: Implications for soil carbon

Abstract

An advance in snowmelt timing in seasonally snow covered ecosystems has a wide range of potential impacts on plant and soil processes. Plants may respond to earlier melt through changes in phenology and altered allocation of resources to growth and reproduction, and earlier snowmelt may impact active pools of soil C such as microbial biomass and dissolved organic C (DOC). In subalpine aspen forests and open meadows in the Wasatch Plateau of the western Rocky Mountains, we manipulated snowmelt timing by adding dust to the snow surface. We obtained a treatment-induced snow-free interval of 6 to 22 days (3% to 11% reduction in snow-covered days). We observed the growth of early and mid-season herbaceous species, measuring above ground biomass, flower and seed counts, and seed mass. We also monitored microbial biomass, DOC, and soil respiration in the days and weeks following snowmelt. We observed generally warmer soil temperatures in the early snowmelt plots compared to controls. However, we found no difference in microbial biomass C or DOC following snowmelt and we found no legacy effect in growing season soil respiration as a result of earlier snowmelt. After three years of repeated treatments, total soil organic C remained unchanged between treatment and control plots. Although earlier snowmelt is likely to have a variety of impacts on subalpine ecosystems, we found no change in plant biomass or reproductive allocation and we found that carbon pools and fluxes were not perturbed by earlier snowmelt. A common expectation is that earlier snowmelt will lead to more frequent freeze-thaw cycles in soils, and studies have shown that freeze-thaw events can have significant but temporary impacts on soil C efflux. This study indicates that subalpine plants and soils may be at least partially buffered from some of the anticipated effects of earlier snowmelt. One direction of continuing research may be to identify adaptive buffers in subalpine ecosystems, an understanding of which may be useful in anticipating and responding to future climate change.