抚育问伐对宁夏六盘山华北落叶松人工林林分生长的影响

研究了不同间伐强度对华北落叶松人工林林分生长的影响，为华北落叶松人工林的合理间伐提供依据．在坡向、海拔一致，林龄为30年的华北落叶松人工林中，选取了9个监测样地，分别代表3种间伐强度：20％、25％、30％，每一种间伐强度3个重复；不同间伐强度林分的保留密度分别为1050、1200、1350株／hm2．同时，在同一林分中设置了3个对照样地．调查了华北落叶松人工林各间伐样地和对照样地中树木的胸径和树高，并通过对林分平均胸径、树高、蓄积生长量进行方差分析、多重比较，以确定不同保留密度下样地与对照样地中各指标的差异，从而认识不同间伐强度的抚育效果．结果表明，林分抚育间伐明显改变了林分的结构，但不同间伐强度林分的胸径、树高、蓄积增长量都存在着显著差异，其中强度为30％的间伐效果最显著．这说明适度地间伐对林木的胸径、树高、蓄积生长均有明显的促进作用．研究表明，不同间伐强度对林分生长量有明显的影响，且林木生长速度、生长量都随着林分保留密度、郁闭度的加大而减小，说明适度抚育间伐措施对华北落叶松人工中龄林的生长有明显地促进作用．

Effects of thinning on the stand growth of Larix principis-rupprechtii plantation in Liupan Mountains in Ningxia

The influences of different intensity of thinning on Larix principis-rupprechtii plantation were investigated to supply useful information on forest management for this tree species. Nine plots in a 30-year Larix principis-rupprechtii stand within the same aspect of slope and altitude were selected to represent three levels of thinning intensity （20%, 25%, 30%） of the plantation respectively, and each level had tree replicates. The density of remained trees in the three levels of thinning plots were 1 050,1 200,1 350 tree hm-2 respectively, and three control plots were also set in the same forest stand. Diameter at breast height （DBH） and tree height （TH） for each tree both in the thinning plots and in the control plots were measured. Then, analysis of variance and multiple-comparison were used to compare the difference in average of DBH, TH and increase in the total volumes among plots, aiming to understand the effects of thinning on stand growth. The results indicated that stand structure was changed after thinning, and there existed a significant difference in the average of DBH, TH and increase in the total volumes among plots, and the 30% of thinning intensity had a great effect on stand structure in this study, compared to the other levels. It meant that rational thinning had a positive effect on the growth of DBH, TH and total volumes in the plantation of this species. Intensity of thinning has a great effect on stand growth, and the rate and amount of growth decreased with increasing density of remained trees and crown density in the stand. It means that rational thinning have a positive effect on the stand growth in half-mature forest of Larix principis-rupprechtii plantation.