Effects of sika deer (Cervus nippon) and dwarf bamboo (Sasa senanensis) on tree seedlings in a cool-temperate mixed forest on Hokkaido Island, Japan

Overabundant deer populations have direct and indirect effects on forest vegetation. For forest regeneration, it is important to identify the response of tree seedlings to deer browsing following a reduction in deer density. We examined the effects of deer density, dwarf bamboo coverage, light availability, and tree species on seedling survival and growth inside and outside deer-excluding fences, from 2009 to 2011 in a cool-temperate mixed forest on Hokkaido Island, Japan. The occurrence probability of browsing was high in the plots with high pellet density. Bamboo coverage decreased significantly with increased pellet density. The survival rate of seedlings was negatively affected by both the occurrence of browsing and bamboo coverage. The growth of seedlings was negatively affected by the occurrence of browsing. Our study showed that deer browsing had both a direct negative effect by decreasing seedling survival and an indirect positive effect by reducing bamboo coverage. These results suggest that we should examine browsing intensity and the response of forest vegetation and recognize the competitive and facilitative effects of neighbouring plants on tree seedlings.