The subnivium is a seasonal refuge that exists at the interface between the snowpack and the ground, and provides a haven for a diversity of species to survive extreme winter temperatures. Much attention has been given to changes in the timing of snow cover extent and duration in seasonally snow-covered environments; however, these broad-scale characteristics do not capture the finer-scale dynamics of the subnivium. To study the factors associated with subnivium development, we quantified three critical phenophases of the subnivium: establishment, maintenance, and disintegration along a latitudinal and land cover gradient in the Great Lakes Region of North America. We hypothesized that subnivium phenophases would depend primarily on snow depth and air temperature, but that these would be mediated by latitude and land cover.
Results/Conclusions
We found that both patterns in establishment and disintegration are affected by latitude more than land cover, but that variability in the timing of early season snowfall events can override the effects of both factors in subnivium establishment. In contrast, disintegration was predictably later in more northerly sites, regardless of interannual variation in weather patterns. We found that the subnivium is the result of a balance between ambient temperature, snow depth, and snow density, but that ambient temperatures constrain the system by determining the frequency of snowfall and inducing changes in snow depth and density. Based on our results, middle latitudes (42°-44°) seem to represent the trailing edge of optimal conditions for subnivium maintenance, while areas in lake effect zones may act as potential refugia for subnivia-dependent species given the predicted shifting climate regimes of the 21st century.