2018 Volume 60 Issue 2 Pages 63-70
We investigated the relationship between vegetation development and sediment transport rates during 13 months after clearcutting of a 100-year old sugi (Cryptomeria japonica) plantation in order to examine the factor of limiting the interaction of vegetation and sediments in the early development process of ground vegetation after logging. Following two hypotheses were examined; 1) vegetation cover controls sediment transport rates, 2) sediment transport inhibits vegetation development. For the first hypothesis, there was no significant relationship between the periodical average vegetation cover and the sediment transport rates per unit rainfall. A decision tree analysis did not also detect threshold values of the vegetation cover to discriminate the sediment transport rate. For the second hypothesis, in contrast, the inclement of vegetation cover standardized within each of their periodical average classes tended to be lower when the periodical sediment transports were larger. A decision tree analysis demonstrated that the standardized inclement of vegetation cover became larger when the periodical sediment transport rates were lower than a threshold of 22.25(g/m/day). These results indicated that the sediment transport rates are the limiting factor of the interaction with the vegetation development at the early stage after clearcutting when the vegetation cover is low and the sediment transport rate is high; the effect of sediment transport to inhibit vegetation development is predominant to the effect of vegetation to control the sediment transport. The analyses also suggested that the spatial heterogeneity of vegetation development was partly affected by the distribution of unstable sediments such generated by road construction and of the remaining course and/or fine woody debris on the logged forest floor.
