Abstract
We used the paired-watershed method to analyze changes in the flow duration curve after forest clear-cutting in the Fukuroyamasawa Experimental Watershed (35°12′ N, 140°06′ E) in University Forest, Chiba, Japan. The watershed is located in a Tertiary formation area and is covered by a mixed plantation of sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa). The annual precipitation and annual mean temperature are 2,170 mm and 14.2°C, respectively. The control and treatment watersheds were both about 1 ha. Daily flow was higher on almost all days after cutting in the treatment watershed, and the increase was greater on the high-flow side than on the low-flow side. However, flow changes on the first through eleventh days after cutting were not obvious. We compared pre- and post-cutting regressions of daily flow in the treatment watershed against daily flow at the control watershed; the slope of the regression lines did not change, but the y-intercepts increased after cutting. The change in daily flow after cutting was smaller than the variation caused by geological differences in the daily flow of several forested watersheds in Japan. The flow duration curves in forested watersheds are influenced by vegetation but are more strongly influenced by geology.
