Plants and plant communities on Kinkazan Island, Northern Japan, in relation to sika deer herbivory

Abstract

Due to an extremely high density of sika deer population (50 deer/km2), the vegetation on Kinkazan Island, northern Japan, is heavily affected. Unpalatable plants including forbs, ferns, and shrubs containing secondary compounds such as Senecio cannabifolis (Aleutian ragwort), Primula japonica (primrose), Pteridium aquilinum (bracken fern), and Leucothoe grayana (Ericaceae) are abundant on Kinkazan Island. The forest structure is modified, the shrub layer is quite poor, and regeneration of the forest is prevented by deer browsing. Forest gaps are formed by strong winds, and the gaps are invaded by Miscanthus sinensis (silver grass). At the density of 100-200 deer/km2, the Miscanthus community is maintained, but it is often concentrated on by sika deer because of great forage biomass, and the deer density often exceeds this level. Thus, Miscanthus cannot tolerate heavy graz ing, and the Miscanthus community is replaced by the Zoysia japonica (Japanese lawngrass) community which is the most grazing-tolerant lawn-type community. The Zoysia community is favored by deer grazing because grazing removes other competitive tall plants while Zoysia japonica can produce leaves under a good light condition. Z. japonica also owes seed dispersal to sika deer. Thus, forest is decreasing and grassland communities, particularly the Zoysia community, are increasing on Kinkazan Island.