The structure of tree quantity, the distribution of diameter at breast height ( DBH), and the stratum structure were analyzed by investigating all trees in 52 enterprise and institution areas in Beijing. Some suggestions on afforestation of enterprise and institution areas were proposed. Results showed that Populus alba, Sophora japonica, Platycladus orientalis,Paulewniafortuaei, Cedrus deodara, Pinus tabulaeformis and Ginkgo biloba in the enterprise and institution areas had higher importance values, which were 0.465, 0.311,0. 188, O. 180, 0. 170, O. 150 and 0. 101, respectively. All the above trees accounted for 54.7％ of the total number of trees and their relative coverage reached 0. 697. The average tree height and average DBH of the arbors at their growth stages were 10.6 m and 21.4 cm respectively. Most tree species were within the range of 10 to 20cm in DBH and 5 to 15m in tree height. The structures of tree height and DBH of the trees were relatively reasonable, but the total number of trees was still lower. Forest communities in the majority of the enterprise and institution areas had not formed mature structures. Severe pruning, poor environmental conditions, and light blocked by buildings were the major limiting factors on the expansion of green space. Some suggestions on planting tall arbors were proposed to achieve the integrated combination of ground space and canopy space, which could effectively increase the volume of the green space in enterprise and institution areas.%在对北京建成区学校、医院、机关附属事业单位、工厂、企业等52个专属单位进行每木调查的基础上,研究了不同类型单位区树木数量结构、胸径等级分布和立木层次结构,提出了单位区绿化发展建议.结果表明,毛白杨(Iv=0.465)、国槐(Iv=0.311)、侧柏(Iv=0.188)、泡桐(IV=0.180)、雪松(IV=0.170)、油松(Iv=0.150)、银杏(IV=0.101)是单位区重要值最高的几个树种,其累计数量占到了研究区树木总株数的54.7%,相对覆盖度累计达到0.697.单位区乔木植株平均高度10.6m,平均胸径21.4 cm,径级区间(10 cm≤DB,H＜20 cm)和立木层次(5 m≤h＜15 m)上分布的植株数量和树种数量最多,单位区现有树木水平径级结构与立木层次结构分布相对合理,但树木数量整体偏少,多数单位区还没有形成一个成熟的群落结构.重度修剪、立地环境差和建筑物阻挡是制约单位区树木三维绿量扩增的主要因素,建议通过补植高大乔木的措施增加单位区绿量空间,实现树冠下地面空间利用和冠层绿量空间拓展的有机结合.
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