Abstract
The effects of shading and thinning rate of upper storey on the growth of Chamaecyparis obtusa Sieb. et Zucc seedlings were studied. Four plots, each 25m×25m, were established in a artificial stand of 45 years old Chamaecyparis obtusa. Three plots were thinned at different thinning rate (B, C, D) and one plot was left unthinned (E) in 1973. In spring 1975, 3 years old Chamaecyparis obtusa seedlings were planted in these four plots and no upper storey plot (A) near these plots.
The relative light intensity under the canopy of upper storey rapidly decreases as the basal area increases till about 35 m²/ha. The diameter growth of underplanting Hinoki decreases as the light intensity decreases. On the height growth, the difference between plot A and underplanting plots is not significant till about 10% of daylight but sharply decreased at lower light intensity. Average dry weight per tree decreases as the light intensity decreases, likes as the trend of diameter growth. Some smaller trees grown in unthinned plot have lower proportion of their total dry weight in leaves so that the growth rate of these trees decrease rapidly.
