Short-term effects of different thinning methods on surface soil erosion of a hinoki (Chamaecyparis obtusa) plantation.

Abstract

We investigated sediment transport rates during 9 months after line and ordinary thinning (scattered tree selection) of 49 years old hinoki (Chamaecyparis obtusa) plantation in order to examine the effects of different thinning practices on surface soil erosion. In the line-thinning site, drastic increase of sediment transport rates was observed immediately after thinning practices at skidding traces, probably due to the low infiltration rate of the surface soil disturbed by repeated skidding. However, the sediment transport rate at skidding traces decreased three months after thinning practices. This might be because unstable sediments were run off by heavy precipitation during the first summer. In the ordinary thinning site, sediment transport rates did not increase significantly after thinning practices, showing lower values compared to those at the logged lines and the skidding traces in the line-thinning site. These results suggested that the ordinary thinning has lower impacts on surface soils, and that the line thinning which promotes aggregated soil erosion should be avoided at the sites of high erosion risks such as steep slopes or volcanic ash deposits for surface soil conservation.