Erosion and/or failure of slope being due primarily to forest road construction activities has become long-term key issues in Okinawa Island as it demands special techniques and high cost for its recovery and maintenance. Early detection and identification of hazardous sites correlated with slope failure is important for forest road network and drainage system planning. This study presents a method to identify and to map slope failure hazardous sites in Yambaru Forest Area (YFA) in the northernmost part of Okinawa Island. The assessment was performed through the detailed analyses of Digital Terrain Model (DTM) and Digital Surface Model (DSM) derived from the Light Detection and Ranging data (LiDAR) at 1m resolution. SAGA CIS software was effectively used to simulate secondary terrain attributes related to erosion development namely LS factor, SP index, and TW index. Vegetation cover assessment was done by the extraction of the Digital Canopy Height Model (DCHM) from the LiDAR data. All parameters were integrated and a slope failure hazard map was produced. For verification, the simulated hazard map was then compared with the ground truth data of slope failure locations. Results indicated that 84.6% of slope failure recorded from field verification fall within the severe identified zone (Class 1 and Class 2) in the simulated map and the analytical method discussed here would become an effective tool for hazard assessment associated with forest road construction in the areas.

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To determine how to mutually use the forest information utilizing the forest geographic information system (GIS) and solve the problem of integrating it, I conducted a questionnaire survey to determine the operative situation of forest GIS among metropolises, districts and forest administration bureaus nationwide amid demands for increased production of domestic lumber via premeditated material production. Consequently, it emerged that integrated computer systems at an early stage would be difficult, given differences in the system and software of the forest GIS which I managed as well as varying numbers of data items. It is thought that the organization and short-term personnel changes affect personnel training to operate GIS. With regard to the exchange of information with external organizations, there were still cities, towns, villages and forestry owner associations which had yet to install forest GIS, but the low budget involved meant system development was considered feasible. I believe the analytical function of GIS was not used very much. It is because it does not accumulate topography data and road line data in order to decide production method by condition of stand, road, and topography. I suggest that we push forward progressively with sharing of forest GIS data and mutual use of GIS between private and national forests.

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