Eighty two plots were set at the riparian forests along the Kinugawa River and its tributaries in Tochigi Prefecture and relationships between tree species composition and site conditions were investigated. By PCA, site conditions of the plots were characterized mainly by the axis representing valley width and altitude, and secondarily by the axis representing relative elevation from water surface. By the cluster analysis, tree compositions were classified into nine: Aesculus type, Zelkova type, mixed type, Alnus-Cercidiphyllum type, Pterocarya type, Toisusu-Salix type, Toisusu type, Ulmus type, and Salix type. At the riparian area with narrow floodplain, Toisusu and Toisusu-Salix types developed on the lower floodplain, and Aesculus type on the higher floodplain and adjacent hill-slope. The montane areas (800-1,400 m in alt.) were characterized by wider riparian area and by diverse microtopographic units, resulting in six of the nine types observed there. Furthermore, major types at the montane areas tended to distribute at lower altitude along the tributaries than the main river. This was attributed to the similar topography of the tributaries to the main river at higher altitude. Thus, diverse microtopographic conditions were realized within wide range in altitude when considering both the main river and tributaries, and should enable diverse riparian forests to establish in riparian habitats of the Kinugawa River basin.

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This study investigated the effects of salvage logging on deer browsing and the impact of browsing on vegetation in a windthrown conifer plantation forest. We compared browsing pressure among three treatments: “log”, fallen logs retained; “planted”, planting after salvaging; and “residual”, residual rows with coarse woody debris that emerged after establishing planting rows. Then, we established a deer enclosure fence for each treatment. The results showed that browsing pressure was highest in the “planted” site, followed by the “residual” and “log” sites. This suggests that deer avoided places where fallen logs were left and that the arrangement of logs influenced browsing. Assessing the impact of browsing on the vegetation, we found increased herbaceous species richness outside the fence at the “planted” site and decreased vegetation height and herbaceous species richness outside the fence at the “residual” site. We did not find an impact of browsing on the vegetation at the “log” site. These changes may have been caused by differences in the species composition, height, and coverage of the vegetation among the treatments, by deer browsing, which decreased the volume of dominant plants, and by seed dispersal by deer. It was suggested that deer browsing can be decreased by keeping large fallen logs, although the effects of deer browsing on the vegetation were complicated and should be subject to long-term monitoring.

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Thirty-years data at the Mt. Naeba Experimental Beech Forest were analyzed to suggest criteria for successful natural regeneration after clear-cutting of the cool temperate forests in Japan. In this forest, partial logging of canopy trees was conducted with different intensities (0, 30, 50, 70, and 100%) and removal of shrub, herb and dwarf bamboo were conducted by different methods (weeding or herbicide with or without soil scarification, and control) in 1968 (totally 25 treatments), and the remnant canopy trees were harvested in 1978. The stem length of the tree saplings and the coverage and the maximum height of the vegetation (for each species) were investigated repeatedly in the quadrats. The probability of trees regenerating successfully (the coverage of tree species >50%) in 2008 was modeled based on the density and the mean height of the saplings and vegetation height in 1982. The probability was primarily determined by the density of saplings within the quadrat in 1982. For example, it exceeded 80% when the density of saplings of 50-cm height were >200,000 per hectare. Thus, current criteria (ca. 30-cm height, >5,000 per hectare) should be too optimistic. For successful regeneration, it is highly recommended to establish much more seedlings by weeding before cutting.

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Dry ravel and soil creep caused by the gravity acting on soil particles are the typical soil movements in steep mountain area. Since these sediment movements result in loss of regolith as well as damage of standing woods, countermeasures are needed for forestry in mountain area. We, therefore, tried to clarify characteristics of sediment movement in steep mountain forests based on field observations. We also investigated effect of wood fences made of thinned woods on the check of sediment movement. Our observations conducted in Akaishi Mountains, central Japan, showed that the freeze-thawing in winter induces active soil movements as the dry ravel and the soil creep. Without influence of active sediment source on upper slopes, wood fences can check soil movement in arterial forests. The area stabilized by the wood fence is considered to depend on the angle of repose as well as the slope gradient.

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In 2010, the number of living trees attacked by the Oak borer Platypus quercivorus was investigated in a Quercus crispula forest which had or had not been attacked by the borer in the previous year. The attack density per tree was correlated negatively with that in the previous year, except for one data that showed the maximum density in each year. Thus, the trees attacked by the borer in the previous year received fewer attacks than non-attacked trees, and the past-record effect of reducing tree mortality approximated 81%. These results suggest that further beetle attack and tree mortality were controlled on the living trees that had been attacked at a high density in the previous year.

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In order to understand the effects of line thinning on forest biota, we compared ant community structure between the line thinned and an adjacent control stand in two Japanese cedar plantations in Hyogo Prefecture. The stand, which was heavily thinned 11 years ago, tended to have more woodland specialists and less habitat generalists compared with the control plot. In the stand, which was lightly thinned four years ago, the opposite trend was observed. The effect of environmental factors on ant species composition was not clear, but there were some effects of the amount of incident light to the forest floor and the biomass of understory vegetation. Our results indicate that more investigation is needed in order to use ant species composition as an indicator of the degree of disturbance and subsequent recovery of forest biota after forest management practices.

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