response of forest floor vegetation and tree regeneration to deer exclusion and disturbance in a riparian deciduous forest, central Japan

The response of forest floor vegetation and regeneration of major tree species to deer exclusion in a riparian forest were studied for 3 years with the interactive effects of natural disturbances. At the start of this study, deer density had quickly increased to a fairly high level (29-31 individuals km-2) during the last decade and had severely reduced the amount of forest floor vegetation in the study area. Dwarf bamboos, which were dominant before, had almost diminished from the forest floor. During the study period, aboveground biomass increased steadily but species diversity did not change much in the exclosures. Outside the exclosures, the seedlings of all tree species were damaged greatly by deer browsing, especially the taller ones. Deer browsing had little effect on the emergence of tree seedlings, but deer trampling might have accelerated emergence indirectly by disturbing the soil surface for some species. Differences in plant responses were also observed for deer browsing and the presence of dwarf bamboo that strongly inhibits the recruitment of tree seedlings. The nine major species were classified into three groups according to the response of seedlings to deer browsing and disturbance. Group 1 consists of the species whose seedling survival is affected by browsing, but seldom by disturbances (Phellodendron amurense, Kalopanax pictus, Quercus crispula and Malus toringo). Groups 2 and 3 consist of species adapted to tree-fall disturbance (Betula spp.) and riparian disturbance (Alnus hirsuta var. sibirica, Ulmus davidiana var. japonica, Populus maximowiczii and Salix sachalinensis), respectively, and seedling survival of these two groups is principally affected by light conditions. The effect of deer browsing on seedling survival and growth was greater for Group 2 than for Group 3.