2017 年 4 巻 2 号 p. 39-46
It is concerned that intensive browsing by sika deer (Cervus nippon) has caused declines and disappearances of vegetations in forest floor, resulting in degradations of forest ecosystems across Japan. To determine the effects of deer browsing on forest ecosystems in Gifu Prefecture, we surveyed the decline of understory vegetation in deciduous hardwood forests in 376 forest stands using the shrub-layer decline rank (SDR), which was assessed by combining the coverage of the shrub-layer vegetation and the presence of signs of browsing by sika deer in each forest stand. We found that remarkable declines of vegetations (i.e., shrub-layer vegetation coverage was less than 38%) due to deer browsing were observed in 31.1% of the surveyed stands. We then estimated the spatial distribution of SDR in deciduous hardwood forests, based on sampled data, using a spatial interpolation method in the Geographic Information System. The results of the spatial estimation indicated that remarkable vegetation declines due to deer browsing could be occurred in 22.2% of the forests (1,133.5 km2), mainly distributed western and central areas of the prefecture. Moreover, our findings indicated that effects of deer browsing on forest ecosystem have started to expand northward and eastward of the prefecture. For conservation of forest ecosystem, we suggest reinforcing sika deer culling in the northern and eastern areas of Gifu Prefecture, where numbers of deer caught were relatively smaller than those in the western and central areas.