Woody Vegetation Succession and Prediction of the Occurrence Cycle of Shallow Landslides on Steep Granite Slopes

Abstract

We investigated woody vegetation succession and the rate of topsoil development on shallow landslide scars on steep granite slopes in Kagoshima Prefecture, Japan. We used our results to predict the occurrence cycle of shallow landslides. For this study, nine shallow landslide scars of ≥40º were selected. The age of the scars ranged from 2 to 49 years. We installed 5 m × 5 m quadrats in the scars and conducted a field study. The results showed that woody vegetation in the quadrats had a smaller Fisher-Williams index of diversity and the rate of evergreen broad-leaved trees than a climax forest. Accordingly, the succession of woody vegetation in the quadrats was not at the level of a climax forest. The rate of topsoil development, based on the relationship between topsoil depth and the time since the occurrence of the shallow landslide, was 0.25 cm/year. Thus, the occurrence cycle of shallow landslides, based on the topsoil depth needed to generate a shallow landslide and the rate of topsoil development, ranged from 200 to 300 years (average 248 years). Our method was effective for predicting the occurrence of shallow landslides on steep granite slopes.