Abstract
In the Nakatsu River basin (3,544ha) in the Tanzawa Mountains of Kanagawa Prefecture, Japan, we analyzed relationships between the residual tendency of the landslides that seen in 1947 and topographic factors using the "Quantification n" method. We classified the landslide areas into two types : a "revegetative" type, which had disappeared by 1993, and a "residual" type, which was still existing in 1993. In the analysis, elevation, azimuth, inclination, cross-sections of slopes and turning points of inclinations were employed as the topographic factors. As a result, the order of the partial correlation coefficients and ranges of the items was elevation > azimuth > turning points of inclinations > cross-section of slopes > inclination, with influence by elevation and azimuth particularly large. Residual tendency was mostly observed at 900m or more a.s.l., and increased with elevation. In azimuth, residual tendency was seen mostly in slopes facing S, SE and W. In slopes in high elevation regions, especially those facing S and SE, it appears that the residual landslide period became so long because invading plants on landslides were not established easily due to disturbance of the surface soil by freezing and melting. In such an area, it may be better to give priority to soil conservation in forest management, especially to promote the growth of the main types of vegetation in a natural forest.
