Stage-dependent effects of browsing by snowshoe hares on successional dynamics in a boreal forest ecosystem

Herbivores transform landscapes and affect succession via selective foraging that alters vegetation composition. In the boreal forest, mammalian herbivores, mainly moose, facilitate a shift toward the dominance of heavily defended species over time, such as white spruce. The effects of moose herbivory are intensified by the browsing of snowshoe hares. However, unlike moose, snowshoe hares also browse seedlings of white spruce. We quantified herbivory by snowshoe hares on white spruce along the Tanana River, interior Alaska, and assessed the effects on white spruce demography via two different herbivore exclosure experiments. We hypothesized that both experiments would show reduced plant density and height growth in the presence of hares. We found evidence of extensive browsing of white spruce seedlings by snowshoe hares, which negatively affected white spruce establishment along the Tanana River floodplain. Previous research has indicated that hares facilitate floodplain succession in the forward direction. However, hare herbivory can also retard succession by depressing white spruce establishment and increase the time individual trees spend in the understory. This stage-dependent effect on successional dynamics via a unique temporal variation in snowshoe hare herbivory may contribute to alternative successional trajectories in the boreal forest.