Abstract
For the problematic erosive tendencies of Chamaecyparis obtuse Endl. (hinoki) forest, fast fragmentation of the scale like leaves due to raindrops striking the soil surface is often referred to. The objective of this study is to evaluate sediment movement in the form of erosion and deposition at three plots set on a steep slope reforested with hinoki in Kochi Prefecture, Shikoku. In case of Plot I having 8 years' observation period, the erosive tendency of whole observation period has turned gentle on the way due to the thinning effect. Fair soil compaction seemed to contribute to an immediate fall in erosion tendency. We found mean erosion heights of 7.412.31 mm per year in three plots during the common observation period, which is higher than that of denuded mountain slopes of weathered granitic rocks. We found mean daily rainfall as an effective rainfall intensity index to evaluate sediment movement tendencies. Sediment movement on the experimental slope occurs even after a little rainfall, which is not usually considered erosive. Most of the deposition was found in the winter season having little rainfall, whereas almost all of the erosion was found in the summer and rainy seasons. As for the preparation of the unstable sediment, the fall of smaller scale soil pillars was found to be the most important factor, and their fall prevails in the winter season.
