Abstract: Objective In this study, the effects of different pruning treatments on the trunk growth, crown changes and trunk shape of young forests of Michelia macclurei, Castanopsis hystrix and Castanopsis fissa were investigated to select their best pruning methods respectively, so as to provide theoretical basis for their pruning techniques.Method The pruning experiment was carried out in 5-year-old pure forests of M. macclurei, C. hystrix and C. fissa. Three pruning treatments and one control were set up: pruning 1/3 (trim the branches below 1/3 of the tree height), pruning 1/2 (trim the branches below 1/2 of the tree height), pruning 2/3 (trim the branches below 1/2 of the tree height), CK (no pruning). After 4 years of pruning, the effects of different pruning treatments on trunk growth, crown changes and trunk shape conditions of M. macclurei, C. hystrix and C. fissa were measured and determined. The analytic hierarchy process was used to comprehensively evaluate their form quality of different pruning treatments.Result Different pruning treatments had no significant effects on the height, DBH, volume and growth percentage of M. macclurei. Pruning 2/3 reduced the DBH, DBH growth percentage and volume growth percentage of C. hystrix. Pruning 1/2 and 2/3 reduced the tree height growth percentage of C. fissa, and pruning 2/3 reduced the volume growth percentage of C. fissa. With the strengthening of pruning degree, the under-branch height and dead branch height of M. macclurei, C. hystrix and C. fissa became higher, while the height of tree crown moving upward and the depth of dead branch layer became smaller. Pruning 1/2 reduced the crown diameter of C. hystrix, and pruning 1/3, 1/2 and 2/3 reduced the crown diameter of C. fissa. With the strengthening of pruning degree, the tree tapering, number of branches and probability of bifurcation of M. macclurei and C. hystrix decreased, while the bifurcation height increased. Pruning 1/3, 1/2 and 2/3 reduced the tree tapering, number of branches and probability of bifurcatione of C. fissa. The comprehensive evaluation scores of different pruning treatments were as follows: for M. macclurei, pruning 2/3 > pruning 1/2 > CK > pruning 1/3; for C. hystrix, pruning 1/2 > pruning 2/3 > pruning 1/3 > CK; for C. fissa, pruning 1/3 > pruning 1/2 > pruning 2/3 > CK.Conclusion The compensation threshold of different tree species is different. At the early-aged stage, the compensation threshold of M. macclurei is higher than pruning 2/3, while that of C. hystrix and C. fissa is lower than pruning 2/3. If pruning exceeds the threshold, it will reduce the growth of tree height or DBH, and ultimately reduce the growth of volume. Different pruning treatments have no significant effect on the crown diameter of M. macclurei during the early age. Pruning 1/2 significantly reduces the crown diameter of C. hystrix during early age, and pruning 1/2 and 2/3 significantly reduced the crown diameter of C. fissa during early age. The under-branch height and dead branch height are characterized that the greater the pruning intensity, the higher the height. Pruning can significantly improve the forest sanitation, outturn percentage, trunk shape quality and form quality of M. macclurei, C. hystrix and C. fissa during early age. At the early-aged stage, the best pruning treatment for M. macclurei is pruning 2/3, for C. hystrix is pruning 1/2, and for C. fissa is pruning 1/3.

Key words: Michelia macclurei, Castanopsis hystrix, Castanopsis fissa, pruning, comprehensive evaluation of form quality