摘 要 ：公路绿化是国土绿化的重要组成部分，对于促进社会经济和自然生态系统的和谐发展具有重要的作用。以北京市顺平路（S305）顺义段两侧绿化的毛白杨(Populus tomentosa)和垂柳(Salix babylonica)群落为研究对象，应用WinSCANOPY For Canopy Analysis冠层分析仪及软件采集、分析照片，研究比较了不同径阶的两种群落光环境特性和冠层结构指标：光合光量子通量密度（photosynthetic photon quanta flux density，PPFD）、总空隙度（gap fraction）、叶面积指数（leaf area index，LAI）、平均叶倾角（mean leaf angle，MLA）等，得出以下结论：不同径阶两种群落的冠层总辐射水平基本相同，林下直射和总辐射随胸径增加而降低，而林下散射没有明显变化规律；毛白杨群落总空隙度随胸径增加先降低后增加。垂柳群落总孔隙度随胸径增加而降低，并且平均值低于毛白杨群落；两种群落叶面积指数都随胸径增加而增加，但是垂柳群落叶面积指数稍大于毛白杨群落；两种群落平均叶倾角随胸径增加而降低，平均值约为32°；从消光系数分析，可以看出毛白杨群落冠层截获光辐射能力较强，林下光环境较差；对比林下散射变化情况与平均叶倾角变化情况，还可看出林下散射在一定程度上受冠层平均叶倾角的影响显著。因此，两种群落相比，毛白杨群落的总光辐射变化更明显，并且比垂柳群落差。如果只考虑光环境，垂柳群落更有利于建立绿化复层群落结构，这为公路绿化建立复层的、多样性的和稳定性的群落结构提供了基础分析和参考。
Abstract:As an important part of territory virescence, road greening will promote social economy and eco-environment harmonious development. This study taked Populus tomentosa and Salix babylonica communities along Beijing Shunping Road(S305) in Shunyi County as research objects and analyzed light environmental characteristics indexes, such as Photosynthetic Photon Quanta Flux Density (PPFD), Gap fraction, Leaf Area Index(LAI), Mean Leaf Angle(MLA) and so on. The results showed that:(1)The total radiation and scattering radiation were basically same for the two communities, but the direct radiation and total radiation under the canopy decreased with DBH increasing. (2)The gap fraction of Populus tomentosa communities firstly decreased and then increased with DBH increasing, but it decreasd with DBH for Salix babylonica communities and the average of the latter was lower than the former. (3)LAI increased with DBH increasing for two kinds of communities, and the average of Salix babylonica communities was bigger. (4)The average of MLA was about 32° and decreased with DBH increasing for both kinds of communities. (5)Light extinction coefficient (k) showed that the Populus tomentosa had a relative higher ability of light interception. (6)And PPFD was closely related to MLA. According to the above results, we concluded that the light environment of Populus tomentosa communities changed larger apparently than that of Salix babylonica communities, and the latter was more suitable for establishing multi-layer vegetation system for road greening if light was the only factor taken into account.