不同造林密度对米老排人工林枝条发育的影响

目的 探究不同造林密度对米老排枝条发育的影响规律，为米老排修枝培育无节良材提供理论依据。 方法 本研究以8年生米老排密度试验林为研究对象，通过调查一级枝条的数量、基径、长度、分枝角、分枝高和方位角等观测数据，分析5种造林密度对米老排林分9 m以下枝条发育以及空间分布的影响。 结果 表明：米老排枯枝层的高度随密度的增大而增高，枝条总量和枯枝数量受密度影响不显著，林分枯枝率随密度的增大而增大，活枝量与密度呈负相关；米老排树干9 m以下枝条基径、枝长和分枝角均随密度的增大而减小；水平方向上，同一密度，不同方位的枝条基径、枝长、分枝角和数量均随方位角的增大先减小后增大，在光照条件较好的方位区间（0~90°或316~360°）内达到最大值；垂直方向上，枝条基径、长度、数量随相对位置的升高先逐渐增大，之后无显著变化。 结论 造林密度对米老排枝条大小的影响显著，高密度（2 500株·hm-2）可以抑制枝条的生长；建议根据培育目的选择合适的造林密度，并采用目标材种培育技术，在幼龄期对优势木及亚优势木进行人工修枝，提高木材质量。

Effects of Planting Density on Branch Development of Mytilaria laosensis Plantations

Objective To study the effects of planting density on branch development and provide references for improving the wood quality of Mytilaria laosensis. Method The effect of planting density on branch development was examined in an eight-year-old M. laosensis plantation with five planting densities. The branch quantity (amount, proportion), morphology (diameter, length and angle of first-branch), position (height and orientation) and branch statues (dead or live) of 80 sample trees (5 033 branches) were investigated. Result The results showed that the dead branch layer increased with the increasing densities. No close relation was found between the amount of total branches or dead branches and the planting density, but the rate of dead branch increased with the increasing planting density. The basal diameter, length and angle of branch under 9 meters decreased with the increasing planting density. In the horizontal direction, the basal diameter, length, angle and amount of branch in same density and different orientation increased at first and then decreased with the increasing position angle. It reached the maximum value in a better illumination condition in the range of position angle (0-90° or 316-360°). In the vertical direction, the amount of branch increased gradually with the relative position and then closed to the uniform distribution. The basal diameter and length of branch correlated positively with the increasing height, and then less change was observed. The branch angle decreased from bottom to top in the vertical direction. Conclusion The diameter of branch is affected by planting density significantly. The branch growth is inhibited by high density (2500 tree·hm-2). It is suggested that the planting density should be chosen according to the cultivation aim, and pruning should be made as early as possible on the dominant or co-dominant trees, so as to improve effectively the wood quality.