黄土区不同密度侧柏人工林树冠二维特征的差异

以陕西省永寿县马莲滩林场22年生侧柏人工林为研究对象，比较分析了林分密度具有明显差异的2组侧柏人工林的树冠二维特征，以期为黄土高原地区不同密度侧柏人工林的合理修枝抚育提供理论依据。结果表明:1) 平均冠幅和平均活枝下高均以密度较小林分（2 080～2 120株·hm^-2）大于密度较大林分（3 560～3 760株·hm^-2），而平均冠长和平均冠长率均以密度较大林分较大；2) 不同密度的侧柏人工林中，相同径阶和相同树高组林木的活枝下高、冠长和冠长率均具有极显著差异，而冠幅只在3 m树高组具有显著差异。表明林分密度对林木冠幅、活枝下高、冠长和冠长率均具有显著影响。因此，对于不同密度的侧柏人工林应采取不同的修枝强度进行人工抚育。

Differences of Crown Two-dimensional Features of Platycladus orientalis Plantation under Different Stand Densities in Loess Area

Compared with diameter at breast height (DBH), tree height,canopy could be more intuitive in reflecting interaction of individual tree with its surrounding environment.In order to provide a theoretical basis for the rational pruning of Platycladus orientalis plantations with different densities, two-dimensional features of P.orientalis plantations (22 years old) with the density of 2 080～2 120 plants·hm^-2 and 3 560～3 760 plants·hm^-2,located in Yongshou,Shaanxi were examined.Low density plantation showed higher mean crown width and mean alive under branch height,but lower mean crown length and mean crown ratio.Alive under branch height,crown length and crown ratio in same diameter class or same height class showed most significant differences between the plantations with different densities.The crown width showed significant differences only in 3 m height class.The results suggested that stand density had significant effects on crown width,alive under branch height,crown length and crown ratio.Therefore,different pruning intensities should be adopted for the plantations with different densities.