Abstract
Low thinning of 26-year-old stands of Sugi (Cryptomeria japonica) was performed to study the effect of the degree of thinning on canopy openness. Thinning in P-2, P-3, and P-4 was repeated twice, four times, and four times respectively, and the thinning ratios based on number of trees after the last thinning were 26%, 51%, and 70% respectively. Before and after thinning, hemispherical photographs were taken at six places in each plot and the Hemiphot method used to measure canopy openness. No differences in the relationship of canopy openness with thinning ratio based on number of trees and in the relationship of canopy openness with thinning ratio based on basal areas were found between the plots. The relationships of the enlargement of canopy openness with thinning ratios based on number of trees, with thinning ratios based on basal area, and with the decrease of the yield ratio were identical for each plot and each relationship could be expressed by a quadratic curve.
