エゾシカの増加が洞爺湖中島の維管束植物相に与えた影響

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We surveyed the vascular flora on the Nakanoshima Islands in Toya Lake, Hokkaido, Japan, during the years 2002-2004. Here, the impacts of an excessive population of sika deer (Cervus nippon Temminck) have lasted for more than 20 years. The present survey found 150 plant species in 68 families on the islands (excluding the species recorded only in the areas impossible for the deer to enter), a decrease to 32.6% of the 460 species surveyed in 1977. The survival ratios of herbaceous, shrub and tree species were 18.8% (n=67), 35.0% (n=14), and 62.5% (n=40), respectively. The survival ratios of herbaceous and shrub species were lower than for tree species. These results suggest that shrub and herbaceous species, which utilize the same space as deer, were more affected by the deer compared to the tree species. Numbers of alien plants did not change since the first survey, and the failure to increase was probably because of heavy foraging pressure. In recent years, deer have started foraging on unpalatable plants such as Cephalotaxus harringtonia var. nana and Senecio cannabifolius. The current findings suggest that the flora on the island change rapidly in response to pressure from browsing deer.
2007-09-10