Relationship between a high density of sika deer and productivity of the short‐grass (Zoysia japonica) community: a case study on Kinkazan Island, northern Japan

Abstract

AbstractAn extremely high‐density (ca. 800 deer km−2) wild sika deer population uses a short‐grass community dominated by Zoysia japonica on Kinkazan Island in northeastern Japan. To explain why the density of wild deer is quite high on the Zoysia community, (1) we quantified the seasonal productivity of the Zoysia community, (2) we compared food availabilities among the plant communities, and (3) we described the habitat selection by the deer in different seasons. Food availability was greater on the Zoysia community than in the forest understory from spring to fall. The productivity of the Zoysia community was high enough to support the actual high density of the deer (814 deer km−2) in summer. However, the productivity markedly decreased in winter, when the deer density decreased to less than half (358 deer km−2) of the summer value. In contrast, the deer density of the adjacent forests was highest in winter (154 deer km−2) and lowest in spring (19 deer km−2). These results suggest that the deer using the Zoysia community in summer left and were “absorbed” into the adjacent forest in winter. If such an adjacent community were absent, many deer would not survive, and consequently the deer density on the Zoysia community in summer would not be so high. This intercommunity movement is particularly important for the deer using a plant community like the Zoysia community, which is highly productive but has a small standing biomass.