Climate change has the potential to alter the strength of plant-consumer interactions, which can limit the ability of plant species to track suitable habitats. In temperate forests, climate change may have the most dramatic effects during winter, as even small increases in temperature can transform ecosystems from snow-covered to snow-free states. Decreased snowfall may create underappreciated changes in biotic interactions, such as seed predation, but these effects may vary across space. For example, deep snow can facilitate small-mammal foraging by providing refuge from predators, but in warmer winters, hotspots of consumer activity may form near alternative predation refugia (e.g., woody debris) in the absence of snow. We tested whether woody debris influences the effect of snow removal on small mammal activity and seed predation. In the winter of 2017-2018, we added Acer rubrum and Acer saccharum seeds to 2m x 2m plots at 10 sites across a 60 km study area in Wisconsin, USA. In each plot, we experimentally manipulated snow depth and woody debris volume, and recorded seed predation after snow retreat in May 2018. We monitored winter small-mammal activity with subnivium camera traps.
Results/Conclusions
Conifer basal area was associated with increased winter small-mammal activity, but only at sites with little ambient woody debris. Winter small mammal activity was associated with greater seed predation of Acer saccharum, but not Acer rubrum. Woody debris addition increased Acer rubrum seed predation, but only in plots with snow removed and at sites with more southern red-backed voles (Myodes gapperi). Our results suggest that as more northern temperate forests experience above-freezing temperatures, spatial variation in woody debris volume may become an important predictor of winter seed predation. Moreover, changes in snow depth could interact with climate-mediated range shifts of key small-mammal seed predators (e.g., M. gapperi) to cause unexpected changes in seed predation. Anticipating biotic interactions in warmer winters will therefore require an understanding of how the effects of reduced snow depth vary over gradients of predation risk. Failing to account for biotic responses to climate change may limit our ability to anticipate climate-mediated shifts in northern temperate forest communities.