中文摘要：

以六盘山南侧的华北落叶松水源涵养林为研究对象，利用标准木树干解析法，研究了21年生低、中、高3种密度（1200、1500和2000株·hm^-2）华北落叶松人工林的生长过程和直径结构。结果表明：华北落叶松3种密度林分在10年生前各项生长指标差异不显著；10年生后的林木直径、单株材积和林分蓄积生长过程明显不同；21年生时，低密度林分的生长状况明显优于中、高密度林分，但树高生长受密度影响不显著；3种密度林分直径分布的偏度系数（Sk）差异较大，高密度林分的Sk（0．338）大于中密度（0．072）和低密度林分（0．015）。前者直径分布偏离正态分布，呈现顶峰偏左的现象；后者的直径分布接近正态分布，密度结构较合理；中密度林分直径分布的峰度系数（K，1．691）大于高密度（1．532）和低密度林分（0．665）。说明中密度林分的林木分化程度比高、低密度林分小；林龄为21年的华北落叶松人工林的合理保留密度应为1200株·hm^-2。

英文摘要：

By the method of sample trees stem analysis, this paper studied the growth process and diameter structure of 21-year-old Larix principis-rupprechtii plantations with the densities of 1200, 1500, and 2000 stems · hm^-2 in the head-water area on the southern slope of Liupan Mountain in Ningxia Hui Autonomous Region. The results showed that there were no significant differences in the growth status of L. principis-rupprechtii stands among the three densities when the stand age was less than 10 years. However, obvious differences were observed in the diameter and timber volume of individual trees and in the stand volume when the stand age was more than 10 years. The tree growth status in low-density stand was apparently better than that in medium- and high-density stands, but the height growth had no significant difference among the three densities. There was a significant difference in the skewness coefficient （ Sk ） of diameter distribution among the stands with different density, being higher （ Sk = 0. 338 ） in high-density stand than in medium-density stand （Sk =0. 072） and low-density stand （Sk =0. 015）. The diameter distribution in high-density stand deviated from normal distribution, with a zenith tending to left, while that in medium- and low-density stands approached a normal distribution, with a more reasonable density structure. The kurtosis coefficient （K = 1.691 ） of medium-density stand was higher than that of high-density stand （ K =1. 532 ） and low-density stand （ K = 0. 665 ）, indicating a lower degree of polarization of tree growth in medium-density stand than in other two stands. The reasonable remaining density of 21-year-old L. principis-rupprechtii plantations was suggested to be 1200 stems · hm^-2.