Spatial heterogeneity and its factors of sediment transport after logging of a sugi (Cryptomeria japonica) plantation

Abstract

We investigated sediment transport rates during 6 months after clearcutting of a 100-year old sugi (Cryptomeria japonica) plantation in order to compare its spatial heterogeneity of sediment transport an uncut stand. After clearcutting, the extremely large sediment transport rate (STR) owing to the possible formation of `the water path' contributed to the higher coefficient of variation (CV) of STR compared to that in the uncut stand. To examine the factors affected the variations in STR, we classified the STRs of the clearcut stand into two categories (high and low STR) based on positive or negative deviation from the mean STR, and compared the forest floor cover by forest residues (woody debris and litter: FCR), litter movement rates, and slopes inclination between the categories. The low STR (negative deviation) had significantly higher FCR and smaller litter movement rates. STR showed a strong negative correlation with FCR. A decision tree analysis demonstrated that STR was low (negative deviation) when the FCR was less than 44.5%. These results suggested that the increase of STR due to the formation of water paths by skidding and the control of sediment transport by scattered forest residues contribute to the heterogeneous sediment transport in the clearcut stand.