Abstract: [Objective] The long-term excessive harvesting of larch forest in Great Xing'an Mountain has caused unbalanced forest structure and decreased stability. In order to promote the forest recovery and stand growth in the region, forest tending with varied thinning intensities were implemented and the optimal thinning intensity was determined to optimize the overall management effect.[Method] In this paper, a total of 10 larch forest plots with varied thinning intensities in Great Xing'an Mountain were studied. Thirty-four indices such as biodiversity, stand spatial structure, canopy structure, photosynthesis, and growth of forest trees were used to describe the basic information of the plots and the mean value and standard deviation of each index were calculated and index differences among the plots were tested with SPSS19.0. Meanwhile, Principle component analysis (PCA) was used to establish the comprehensive evaluation system of forest tending effects and the management effects of the forest plots with different thinning intensities were evaluated.[Result] There were significant differences in Shannon-Wiener diversity index and Pielou evenness index among the forest plots with varied thinning intensities. The species diversity index was relatively higher for the plots with thinning intensity ranging from 20.86% to 40.01%. The stand spatial structure also varied with thinning intensity. For the plots with thinning intensity of 12.52%, the stand distribution, mingling degree, neighborhood comparison, and stand layer index showed larger value while the competition index and open degree were small. For the canopy structure of the sample plots, there were no significant differences in cap fraction, leaf area index, total site factor, and PAR over canopy. However, the PAR under the canopy differed significantly among the sample plots. The best canopy structure was achieved in the plots with tending intensities ranging from 12.52% to 34.38%. The photosynthesis indices differed significantly among the plots with varied tending intensities and the photosynthesis effect was relatively better for the plots with tending intensities ranging from 12.52% to 27.85%. The growth rate of the three regenerated seedlings increased first and then decreased over time for all sample plots with varied tending intensities. However, the survival rate of the seedlings didn't follow any specific rules for the plots with varied tending intensities. The regenerated seedlings grew well for the plots when the thinning intensity ranged from 6.23% to 20.46%. The comprehensive scores of the management effect of the forest plots with varied tending intensities were as follows:0.00%(-0.18),6.23%(-0.10),12.52%(0.37), 20.86%(0.80),27.85%(0.35),34.38%(-0.39),40.01%(0.33),50.61%(-0.51),59.92%(-0.01),67.25%(-0.65). The higher the score, the better the management.[Conclusion] The management effect with thinning intensities of 20.86% was the best among the larch forest plots in Great Xing'an Mountain. The evaluation results provide references and guidance for the management of larch forest in Great Xing'an Mountain.

Key words: Great Xing'an Mountain, timber forest, thinning intensity, management effect, principle component analysis