Diverse effects of sika deer are evident in the forest vegetation of the Chichibu Mountains. The cover of the lowest level of understory plants in the riparian forest of Nakatsugawa in the Chichibu district of Saitama prefecture was over 90% in 1983, but had decreased to only 3% by 2004. Plant cover values of only 1% were common in the early years of the current century. Toxic plants, including Scopolia japonica, were notable exceptions to the general decline in forest floor vegetation. The decreases in plant populations are likely to be related to sudden increases in deer population density detected after 2000 by cervid researchers in this area. Plants that remain after heavy grazing tend to be diminutive and have short growing seasons. It is, therefore, likely that, in addition to reducing overall vegetation cover, the deer are responsible for shifts in plant growth forms and life cycles.

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Severe browsing pressure from deer may have great effects on the regeneration dynamics of woody seedlings by affecting seedling mortality and seedling demography. This study quantified the seasonal impact of deer browsing on the relationship between seedling survival and the timing of seedling germination. We established a fenced deer exclosure in a cool-temperate forest in Chichibu that experienced browsing pressure from deer. Newly germinated seedlings of the dominant beech, Fagus japonica, were marked and monitored frequently in the fenced plot and outside the deer fence (open plot). To compare the demography of current-year seedlings, the effects of the timing of germination, light conditions, and total seedling density in each monitoring quadrat were analyzed considering their differences between the two types of plots. The survival rate at the end of the growth period was significantly lower in the open plot (2.0 %)thaninthe fenced plot (9.4 %), mainly because of deer browsing (73.8 % of the total mortality in the open plot). Intensive browsing was observed only during the early growth season, while damping off was the major cause of mortality in the fenced plot (79.0 % of total) during the middle season. Statistical analysis detected opposite effects in the open and fenced plots; early germination was disadvantageous and advantageous for survival, respectively. Seedling demography relating to the advantage of the timing of germination may change depending on the impact of deer browsing, which has clear seasonality.

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The vegetation of Misen Mountains located in the western region of the Shimane Peninsula was investigated at 16 study sites. The purpose of the investigation was to discuss revegetation and management method for forests damaged by the pine wilt disease on Misen Mountains. Twenty-nine species of evergreen trees and 42 species of deciduous trees were identified in the tree and sub-tree layers. The dominant species with respect to number and basal area were Vernicia cordata (Thunb.) Airy Shaw, Camellia japonica L., Neolitsea sericea (Bl.) Koidz. The total estimate for C. japonica and N. sericea in the shrub layer was high, similar to that in the tree and sub-tree layers. Therefore, these trees are the species to be able to grow up in habitat by deer. In contrast, the total estimate for V. cordata and Pinus densiflora Sieb. et Zucc. in the shrub layer was low. Thus, if a protective fence for deer is not established, then the vegetation of this area will transform into that of an evergreen forest. The evergreen forest has low species diversity, and the plant species commonly found in the forest are C. japonica and N. sericea.

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Recently, deer overbrowsing dramatically decreases understory vegetation in forested areas. Also, the deer impact leads riparian vegetation, which originally covers above headwater streams in summer, to be devastated. Riparian vegetation acts important roles linking forest and stream ecosystems by controlling soil erosion, and by providing terrestrial invertebrates to stream as food resources for fishes. Soil erosion activation would induce expansion of fine sedimentation on streambed, and subsequent decrease in diversity of benthic invertebrates in aspect of inorganic materials. Meanwhile, in aspect of organic materials, soil erosion activation would also increase an input of allochthonous organic matter derived from forests that cause changes in nutrient cycling within stream ecosystem. The former impact would be heterogeneously occurred in streams because distribution of fine sediment depends on stream power determined by fluvial geomorphology. Thus for detecting impacts of sediment runoff caused by deer overbrowsing on stream ecosystem, approaches with the view from hydrology and fluvial geomorphology coupling with ecology would be important. On the other hand, changes in quantity and quality of terrestrial invertebrates provided from riparian forest to stream might influ-ence stream fishes and their original ecosystem through biological chain in forest-stream ecosystem.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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In this study, the authors monitored the size of Sasa veitchii (Carriere) Rehder var. hirsuta (Koidzumi) S. Suzuki seedlings grown under various light conditions (five experimental plots with relative solar radiation levels of approx. 90, 73, 55, 28 and 15 %) in order to clarify the relationship between light conditions and growth. The results showed that the growth rate of above-ground and underground organs was at its highest with a relative solar radiation level of around 55 %, and that the rate diminished below and above this level. In a secondary forest (a natural habitat of the species), the relative solar radiation in a canopy gap (44-56 %) was significantly greater than that at a closed-canopy site (16-32 %). The results obtained suggest that light conditions influence the growth of above-ground and underground organs for Sasa veitchii var. hirsuta seedlings, and that sites with favorable light conditions, such as canopy gaps, are advantageous for seedling growth in natural habitats. Rhizome emergence in one-year seedlings and rhizome expansion in two-and three-year seedlings were observed in individual experimental plots. The results obtained here suggest that the growth pattern of Sasa veitchii var. hirsuta seedlings involves vigorous rhizome extension from the initial stage of regeneration regardless of light conditions.

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[in Japanese]

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