Abstract
The transition of shallow landslides that has occurred after clear-cutting beech (Fagus crenata BLUME) stands and planting conifers (Cryptomeria japonica D.DON or Larix leptolepis GORD), on heavy-snow mountain slopes was investigated using aerial photographs. The number, the area and the range of shallow landslides increased for more than 10 years. However, heavy rain or heavy snow initiating the landslides was not found during this period. Small shallow landslides, less than 100 m2, held a greater part in number through the survey duration. The area of shallow landslides increased according to data collected in the years after afforestation. However, the area of shallow landslides changed in very little in the area that afforestation was not carried out. As a result, the occurrence process of shallow landslides is concluded as follows : 1) the glide of snow cover was restrained by the stumps and the effect of the stump roots on slope stability emerged in the several years after the clear-cutting. 2) the glide of snow cover became obvious with the decrease of the stumps and the effect of the stump roots on slope stability deteriorated. 3) the glide of snow cover was restrained by ground clearance and the frictional resistance increased at the bottom of the snow cover be cause of weeding. 4) the growth of planted trees was not enough to restrain the glide of snow cover and affected slope stability for several years after planting. 5) the brush wood decayed and the restraint function of the glide of snow cover was lost several years after afforestation. 6) the shallow landslides resulted in shear fracture by the annual snow displacement.
