Abstract
The effects of thinning on canopy interception loss, evapotranspiration, and runoff were investigated by a paired
catchment experiment in a small headwater catchment in Japan. A 0.88-ha catchment covered with a Chamaecyparis obtusa plantation that was planted in 1986 was intensively thinned in March 2009 following a 3-year calibration period (2006-2008). To avoid disturbing the soil surface, thinning was conducted by forest workers using chainsaws, and the thinned trees were left on the forest floor where they fell. Thinning removed 50 % of the trees, 30 % of the timber volume, and 22.5 % of the basal area. Canopy interception loss decreased by 4 % in the first year after thinning, and it returned gradually to the pre-thinning level for 3 years. The maximum increase in the annual runoff, 147 mm, occurred in the second year after thinning. The mean annual increase in the runoff during the post-thinning period (2010-2012) was 54 mm, although this was not statistically significant. The mean annual evapotranspiration significantly reduced by 140 mm, and the reduction was especially large during the growing season. In conclusion, it seemed that the intensive thinning in a small headwater plantation was effective to increase net precipitation and stream water for a short period.
