We carried out field surveys to study the effect of Japanese black pine trees on sediment yield caused by sheet erosion during a period of low volcanic activity (July 2008 to June 2009). As well, we investigated the differences in sediment yield caused by sheet erosion during periods of heightened (July 1984 to June 1985) and low (July 2008 to June 2009) volcanic activity on a hillside slope of Mount Sakurajima. The amount of sediment yield caused by sheet erosion measured on a slope covered by Japanese black pine trees during the low activity period was about 48 percent of that measured on a slope covered by broadleaf trees during the same period. It was about 2 percent of that measured on a bare land slope during the same period. The amount of sediment yield caused by sheet erosion measured on a slope covered by Japanese black pine trees during the low activity period was much less than that measured during the heightened activity period. The reason for this large decrease in sediment yield caused by sheet erosion during the low activity period was thought to be to the result of the increase of infiltration capacity and the decrease in the magnitude of the surface runoff caused by the recovery of vegetation following an ebb in volcanic activity.

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Between 1991 and 1995, the Mt.Unzen volcano erupted with numerous pyroclastic flows; the flow deposits thickly covered wide areas of the volcano's hillside slopes and radically altered the hydrologic and erosion regimes of the area. As a result, debris flows have frequently occurred in the hillside rivers of Unzen-Fugendake. The frequency and the magnitude of debris flow occurrences decreased after 1994 because of the recovery of infiltration capacity, due to erosion of fine surface tephra. Vegetation recovery was caused by active revegetation works using helicopters. We investigated the impact of recovering vegetation on infiltration capacity and surface roughness based on a field study. Revegetation on devastated hillside slopes increased infiltration capacity and surface roughness, and both infiltration capacity and surface roughness increases were considered to contribute to a decrease in overland flow.

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To determine the recurrence of sediment discharge in the riparian zone of a granite basin in northwestern Kagoshima based on analysis of terrace deposits, aerial photograph interpretation, soil survey and soil profile analysis were carried out. Slope failure has occurred repeatedly in the basin. Slope failures were distributed mainly on slopes >30 degrees in the lower and middle reaches of the basin, and occurred both at sites of previous failures and sites where no previous failures have been observed. Number of sediment discharge events via bed load transport and debris flow was between 4 times and 7 times based on terrace deposit analysis, and relatively large-scale sediment discharges have also occurred several times. The recurrence of sediment discharge was correlated with slope failure in the basin.

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Forest management practices for soil and water conservation was investigated to address current forest management related issues in Japan. This case study was conducted in the Ehime University Forest, Ehime Prefecture, Japan. The main objective was to find the forest management practice as to control soil erosion in artificial forests in the studied area. Among the forest characteristics analyzed in this paper figure forest type (natural forest and artificial Japanese cedar and Japanese cypress) in one hand and on stand density of Japanese cedar and cypress in the other hand. Relative yield index (Ry) was used as an indicator of stand density to reflect the degree of management operations in the watershed. For each forest characteristic (forest type and stand density), soil loss was measured. Data analysis was conducted using General Linear Model Analysis of Statistical Package for the Social Sciences in order to test whether differences in soil loss were statistically significant in different treatments after different rainfall amount and intensities, followed by Tukey's HSD test in case of significance. Multiple regression analysis was conducted to compare soil loss among those different forest conditions which mainly differ from the degree of forest management practice based on thinning operations. Findings showed that areas having experienced forest thinning operations showed lower values of soil loss in comparison to those without any operations. The best scenario of forest management was found in Japanese cedar plantations having Ry between 0.60 and 0.70, followed by the same plantation with Ry between 0.50 to 0.60 and in Japanese cypress plantations having Ry between 0.60 to 0.70. Thus, an appropriate forest management operation is needed not only for timber productions but also for soil conservation which can be insured by stand density control.

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Possible use of alternative broadleaf trees to Pinus thunbergii is examined as one method to reduce the cost for the control of pine wilt in P. thunbergii coastal forests in Japan. However, tree species that are tolerant to the severe coastal environment and have as large maximum tree height as P. thunbergii are unknown. Therefore, to retain canopy height, constructing a coastal forest from a single tree species other than P. thunbergii is not possible. Hence, dividing the site into zones of tolerance to the severe environment and choosing appropriate trees with high tree height for each zone was necessary. Then, species with the necessary characteristics for zoning were arranged based on site investigation and a literature search. Tree height of P. thunbergii was also used as an index for the zoning, in which geographical and surrounding features of the site were not controlled. As a result , finding tree species suitable for each zone was possible based on the existing height of P. thunbergii trees.

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The growth form of coastal black pine (Pinus thunbergii) forest, in the coastal city of Fukuoka, was investigated to provide information for disaster mitigation. These forests provide windbreak against high wind and salt spray. In each stand, growth of shoot, branch, crown and the relative light intensity were measured. The largest biomass occurred in current-year shoots (the outer most shoot of a branch) and current-year shoot length was related to the relative light intensity. The current-year shoot biomass, branch biomass and crown biomass were all proportional. The current-year shoot biomass ratio in the lower to upper crowns was related to the crown length ratio and to the mean of relative light intensity from bottom to the top of crown. Crown length ratio became smaller at higher stand density as current-year shoot growth was restricted by neighboring trees. In low-medium density stands, the crown biomass decreased with increasing stand density, but crown biomass increased slightly in high-density stands. As crown length ratio and crown biomass influence the efficacy of disaster mitigation of the forest, the function can be enhanced by adjusting stand density to optimize these crown elements that provide high levels of windbreak.

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To protect forests as carbon sinks and provide best practice guidelines for restoration projects of coastal dune forests, this work was carried out in Jumundo-ri, Gangwha-gun, Korea. In this work, the methods such as tree planting and hedges for windbreak and sand dune fixation were used to restore coastal forests on a budget of 132 million won for 1.3 hectares in area. Since then, field monitoring has been conducted to evaluate the success of restoration work.

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