Snow cover manipulations alter survival of early life stages of cold-temperate tree species

Projections of future climate suggest increases in global temperatures that are especially pronounced in winter in cold-temperate regions. Thermal insulation provided by snow cover to litter, soil, and overwintering plants will likely be affected by changing winter temperatures and might influence future species composition and ranges. We investigated effects of changing snow cover on seed germination and sapling survival of several cold-temperate tree species using a snow manipulation approach. Post-winter seed germination increased or decreased with increasing snow cover, depending on species; decreased seed germination was found in species that characteristically disperse seed in summer or fall months prior to snowfall. Post-winter sapling survival increased with increasing snow cover for all species, though some species benefitted more from increased snow cover than others. Sapling mortality was associated with root exposure, suggesting the possibility that soil frost heaving could be an important mechanism for observed effects. Our results suggest that altered snow regimes may cause re-assembly of current species habitat relationships and may drive changes in species' biogeographic range. However, local snow regimes also vary with associated vegetation cover and topography, suggesting that species distribution patterns may be strongly influenced by spatial heterogeneity in snow regimes and complicating future projections.