2023 Volume 105 Issue 11 Pages 338-343
In October 2018, spur road construction and small-area thinning were conducted in No. 2 (along the ridge) and No. 4 (near the stream) of the Kamabuchi experimental watershed. Logging rates by volume were estimated at 3.5％ and 4.4％ respectively. To assess the effects of small-scale practice on water runoff in snowy regions, we compared monthly runoff before and after thinning. In the analysis of the monthly runoff ratio to the No. 1 control watershed, the runoff ratio in No. 4 increased after thinning in June only. However, No. 4 had water seepage problems, and the monthly runoff ratio was positively correlated with monthly precipitation. The increased runoff is likely due to several years of high precipitation after thinning. The monthly runoff ratios in No. 2 and No. 3 gradually increased in August, possibly unrelated to the thinning. Then the relationships between the monthly runoff in the No. 1 and the other three watersheds were analyzed for the three seasons (midwinter, snowmelt, and warm seasons). No differences were observed before and after thinning in any season or watershed. Given the limited tree removal during small-area thinning, its impact on water runoff is considered insignificant.
