Abstract: Taking mixed forest of artifical Pinus koraiensis and natural broad-leaved trees  as test material, among which the P. koraiensis was 15 (stage I) and 22 (stage Ⅱ) years old respectively, and was in the same succession layer, the height and diameter increment during 4 years experimental period and the aboveground biomass (AGB) at the 4th experimental year for P. koraiensis were measured in the opening degree (K=1.0, 1.5, 2.0) regulation experiment. The periodic increment of basal diameter (BD)/diameter at breast height (DBH), tree height and AGB of P. koraiensis trees were highest in the opening degree K=1.0 treatment. The opening degree K=1.5 and K=2.0 treatments promoted the annual increment of P. koraiensis, with the effect increased along with the experimental period elongation and approached or exceeded that of K=1.0 treatment. The stem biomass proportion of P. koraiensis trees was significantly higher in K=1.0 treatment than that in the other treatments and the control in stage I, but no significant difference among treatments was found in stageⅡ. The ratio of branch to needle biomass in all opening degree treatments was also significantly higher than that in control in stage I, but no significant difference in stage Ⅱ. The proportion and distribution of needles in different ages differed in the two stages. It was concluded that opening degrees of 1.0-2.0 were all suitable for the growth of P. koraiensis of 15-22 years old trees planted  under secondary forest.

Key words: Pinus koraiensis, opening degree, quantitative regulation, diameter and height increment, biomass