北京5种典型风景游憩林的大气颗粒物吸滞特征

Characterization of Retention of Atmospheric Particles by Five Typical Scenic Recreational Forests in Beijing

【目的】探究不同树种在叶片和冠层尺度上吸滞大气颗粒物的特征,解析相同污染背景下不同树种单叶和林分冠层对大气颗粒物吸滞特征的变异,为营建能够高效吸滞大气颗粒物的城市森林提供理论依据。【方法】对北京市五环路周围具有代表性的平原风景游憩林进行调查后,选择奥林匹克公园内5片典型风景游憩林(华山松-银杏混交林、毛白杨-白蜡混交林、旱柳纯林、毛白杨纯林、多树种复层针阔混交林)作为研究对象,采用洗脱称量粒度分析法得到各树种单位叶面积大气颗粒物吸滞量,通过叶面积指数计算每公顷各树种对不同径级颗粒物的吸滞量,依据各树种冠层占整个林分冠层的面积比例计算纯林或混交林单位面积林分对不同径级颗粒物的吸滞量。【结果】不同林分各树种叶片吸滞大气颗粒物的粒径分布特征存在显著差异,单位面积叶片颗粒物吸滞量在树种间的差异随颗粒物径级和林分类型有所改变。单叶尺度上,各树种对不同径级大气颗粒物的吸滞能力综合排序为银杏>圆柏>元宝枫>栾树>华山松>侧柏>白蜡>旱柳>毛白杨。不同林分冠层对大气颗粒物的吸滞能力差异明显,相差倍数高达20倍左右;各类型林分单位面积的大气颗粒物吸滞量大小不随颗粒物径级而变化,对所有径级颗粒物均为华山松-银杏混交林的吸滞量最高,然后依次为多树种针阔混交林、旱柳纯林、毛白杨-白蜡混交林和毛白杨纯林。【结论】本研究9个树种中,银杏、圆柏和元宝枫为高滞尘树种,栾树、华山松和侧柏为中等滞尘树种,白蜡、旱柳和毛白杨为低滞尘树种;能够对大气颗粒物进行高效吸滞的林分结构特征为含多个高滞尘树种+具有多层林冠+林木疏密相间,欲使城市森林发挥其大气颗粒物吸滞效能,需同时关注高滞尘树种选择及合理林分结构设计。

【Objective】This study aimed to characterize the retention of atmospheric particles by different tree species at both the leaf and canopy scales by the analysis of the variation in the retention of atmospheric particles by individual leaves and forest canopies of different tree species under the same pollution background,therefore to provide a theoretical basis for creating urban forests that can efficiently retain atmospheric particles.【Method】A survey was carried out on representative scenic recreational forests in plain areas around Beijing’s Fifth Ring Road,five typical scenic recreational forests in the Olympic Park(Pinus armandii-Ginkgo biloba mixed forests,Populus tomentosa-Fraxinus chinensis mixed forests,Salix matsudana pure forest,Populus tomentosa pure forest,and multi-species and multi-layer conifer-broadleaf mixed forest)were selected for the study.The elutionweighing-particle size-analysis method was used to measure the amount of atmospheric particles retained per unit leaf area of each tree species.The leaf area index was used to calculate the amount of particles retained by different tree species per hectare for different particle size categories.Based on the canopy area ratio of individual species to the entire forest,the retention amount of different particle size categories per unit area of pure forest or mixed forest was calculated.【Result】There are significant differences in the particle size distribution of atmospheric particles retained by the leaves of different tree species among different forest types.The retention amount of particles per unit leaf area varies among tree species with particle size categories and forest types.At the leaf scale,the comprehensive ranking of the ability to retain atmospheric particles with different particle size categories is:Ginkgo biloba>Juniperus chinensis>Acer truncatum>Koelreuteria paniculata>Pinus armandi>Platycladus orientalis>Fraxinus chinensis>Salix matsudana>Populus tomentosa.The ability of different forest canopies to retain atmospheric particles differs significantly,up to a 20-fold difference.The ranking of the amount of atmospheric particles retained per unit area of different forest types does not change with particle size categories.For all particle size categories,the retention amount is the highest in the Pinus armandi-Ginkgo biloba mixed forest,followed by multi-tree conifer-broadleaf mixed forest,Salix matsudana pure forest,Populus tomentosa-Fraxinus chinensis mixed forest,and Populus tomentosa pure forest.【Conclusion】Among the nine tree species studied,Ginkgo biloba,Juniperus chinensis,and Acer truncatum are high dust-retention species;Koelreuteria paniculata,Pinus armandii,and Platycladus orientalis are medium dust-retention species;Fraxinus chinensis,Salix matsudana,and Populus tomentosa are low dust-retention species.Additionally,the study identifies forest structure characteristics that can efficiently retain atmospheric particulate matter:multiple high dust-retention species+multilayered canopy+staggered tree density.To maximize the dust retention effectiveness of urban forests,attention should be paid to both the selection of high dust-retention tree species and the reasonable design of forest structure.