Abstract: [Objective] In this study,the effects of thinning on Quercus wutaishanica trees form quality were investigated by the analytic hierarchy process in Huanglong Mountains in order to provide theoretical basis of trees form quality evaluation system and thinning on Q. wutaishanica on Loess Plateau.[Method] Experimental sample plots, which are the heavy thinning (keeping canopy density of 0.6), medium thinning (keeping canopy density of 0.7), light thinning(keeping canopy density of 0.8) and control plots (canopy density of 0.9) on Q. wutaishanica forest in Huanglong Mountains of the Loess Plateau were set up. In order to keep invariant canopy density of different thinning intensities of the experimental sample plots, every three years proceed on a tending thinning. The Q.wutaishanica form quality evaluation system was constructed by using the analytic hierarchy process (AHP), with growth situation(height mean increment, DBH mean annual increment, crown diameter ratio, health condition), stem form situation (ratio of height to diameter, tree tapering, stem straightness, bifurcation situation), lateral branch situation (natural ability of self thinning, lateral branch number, index of branch coarse, average base diameter of branches) as Q.wutaishanica form quality evaluation index, calculated Q.wutaishanica trees form quality scores of comprehensive evaluation with the heavy thinning (keeping canopy density of 0.6), medium thinning (keeping canopy density of 0.7), light thinning(keeping canopy density of 0.8) and control plots (canopy density of 0.9).[Result] The stem form situation was the most significant influencing for the tree form quality with the relative contribution rate of 0.653, followed by growth situation, which influenced the tree form quality had the relative contribution rate of 0.285, the less influencing of lateral branch situation for the tree form quality with the relative contribution rate of 0.062. Weights with all the evaluation indexes of Q.wutaishanica form quality evaluation were in sequence of stem straightness (0.344 6) > bifurcation situation (0.227 1) > health condition (0.190 7) > DBH mean annual increment (0.051 3) > ratio of height to diameter (0.046 3) > natural ability of self thinning (0.037 7) > tree tapering (0.035 2) > height mean increment (0.031 6) > average base diameter of branches (0.012 6) > crown diameter ratio (0.011 4) > index of branch coarse (0.008 9) > lateral branch number (0.003 0); Comprehensive evaluation score was in sequence of medium thinning (92.892) > light thinning (83.314) > heavy thinning (79.644) > control plots (74.376), trees form quality score firstly increased and then decreased with the increase of thinning intensity so that medium thinning had the highest score and the form quality of Q.wutaishanica was the best.[Conclusion] Quercus wutaishanica trees form quality were promoted by thinning, and the height mean increment and health condition of the form indexes increased with thinning intensity, and ratio of height to diameter decreased with increasing thinning intensity. Compared with the control, the medium thinning and heavy thinning had significant influence on the crown diameter ratio, lateral branch number and average base diameter of branches.The thinning had significant influence on the stem straightness and bifurcation situation. The best thinning intensity for form quality of Q.wutaishanica was medium thinning (keeping canopy density of 0.7), followed by the light thinning(keeping canopy density of 0.8), the heavy thinning (keeping canopy density of 0.6) being the last,which should be suitable for application in Q.wutaishanica forest tending thinning. With AHP to establish the trees form quality evaluation system can provide the basis for other species form quality evaluation.

Key words: tending thinning, form quality evaluation, analytic hierarchy process, Quercus wutaishanica