The Effect of Thinning on Form Quality of Pinus koraiensis Plantations

Taking Pinus koraiensis plantation of Linkou Forestry Bureau in Northeast China as the research object, 3 evaluation factors for growth situation, stem shape and branching conditions, including 11 indicators of height mean increment, DBH mean annual increment, crown diameter ratio, ratio of height to diameter, tree tapering, bifurcation ratio, loose knot ratio, natural ability of self-thinning, lateral branch number(> 1.5 cm), index of branch diameter, average base diameter of branches were used as the evaluation indicators for P. koraiensis form quality. Analytic Hierarchy Process(AHP) was used as the main analysis method to explore the influence of different thinning intensities(heavy thinning: plant amount intensity 65%, the accumulation intensity 43%; medium thinning: plant amount intensity 50%, the accumulation intensity 28%; light thinning: plant amount intensity 40%, the accumulation intensity 18%) on the trees form quality of P. koraiensis. The results indicate that the highest comprehensive form quality score of 73.427 was obtained for medium thinning, which showed the best form quality that the quality evaluation grade isⅡ, 68.114 for heavy thinning with grade Ⅲ, 59.150 for light thinning with grade Ⅳ, and 43.432 for the control group with grade Ⅴ. The stem shape had the greatest influence on the trees form quality of P. koraiensis, accounting for about 65.5% according to the judgment matrix of form quality indicators. Appropriate thinning of closed P. koraiensis plantation can effectively improve the habitat of reserved trees and improve the trees form quality, which has important guiding significance for the production and management of P. koraiensis plantation.