Study On Environmental Effect Of Common Road Afforestation Trees In Nanjing

Urban road green space system is an important part of the urban forest. From the angle of ecological function of usual road green plants in Nanjing City, this thesis, based on field observation and laboratory analysis, gives a detailed study of the dust detention amount of some road green plants and their capacity of absorbing SO2 and Cl2 as well as the property of anti-frigidity. By means of analytic hierarchy process, the environmental effect of road green tree species is evaluated and some optimal measurements on the selection and arrangement of the tree species are suggested. The result of the study shows that:(1)There is great difference on the amount of the dust detention among different tree species. In the same sampling place, the amount of dust detention of most tree species changes seasonally and the regular pattern follows: winter>autumn>spring>summer. It is clear that in winter the amount of dust detention is the highest. For different tree species, the study shows that the shrub has the highest amount of dust detention in aspects of unit area dust detention, unifoliate dust detention and dry weight dust detention. Then the evergreen trees have lower amount of dust detention and the defoliate trees have the lowest. Besides, there is also great difference on the amount of dust detention among different trees. Take the amount of unifoliate dust detention for example. The amount of unifoliate dust detention of Fatsia japonica is 9132.4319mg while Acer palmatum is only 0.3324mg. Even in the same species, different trees still shows great difference on the amount of dust detention. The difference on the amount of unit area dust detention between Ligustrun quihoui and Osmanthus fragrans could be tens of times. Different unit of measurement can also influence the amount of dust detention of the green tree species.(2)There is great difference on the amount of leaf sulfur content for different tree species. The usual pattern is shrub> defoliate trees> evergreen trees. On the whole, the sulfur dioxide pollution near Refinery of Sinopec Jinling Petrochemical Corp, Ltd. (originally Nanjing Refinery) and Xinzhuang Section of Nanjing—Zhenjiang Road is more serious than the pollution near Nanjing Forestry University and Zhongshan National Park. In the same sampling place and for the same tree species, the amount of washed-leaf sulfur content is higher than that of unwashed-leaf. Moreover, in spring and autumn, the amount of leaf dust detention and the amount of leaf sulfur content clearly have some relevance.(3)In the same sampling place, for the amount of chlorine content of different tree species, the usual pattern is that the defoliate trees have the highest amount of chlorine content, and the shrubs have lower, then the ever green trees have the lowest. Through the analysis of variance on the amount of leaf chlorine content of different tree species, the testing probability Pr>F=0.0023, which is less than the given significance levelα=0.05 proves that there is great difference among different tree species. Generally speaking, it is mainly because of the different biological characteristics of those trees. In order to further analyze the reason for the difference, the author of this thesis made some multiple comparisons. And the result shows that the amount of chlorine content of Ligustrun quihoui and Maqnolia grandiflora is much higher than the other tree species. The amounts of chlorine content of Acer palmatum, Populus Canadensis, Fatsia japonica, Osmanthus fragrans, Platanus hispanica and Buxus sinica do not have too much difference. In addition, the amount of chlorine content of Cinnamomum camphora and Viburnum awabuki is much lower than the other tree species.(4)The study of the property of anti-frigidity of different tree species indicates that through the LT50, these tree species can be divided into four categories. Pittosporum tobira, Maqnolia grandiflora, Aucuba japonica, Var. variegate and Cinnamomum camphora belong to the first category, of which the LT50 is the lowest and the property of anti-frigidity is the best. The second category includes Fatsia japonica, Osmanthus fragrans, Lorpetalum chinense. The property of anti-frigidity of these trees is also relatively good. Ligustrun quihoui, Viburnum awabuki and Buxus sinica are in the third category. The LT50 of them changes from-8.7795℃～-7.8803℃and their property of anti-frigidity is in the intermediate level. Ligustrum Lucidum Ait is in the fourth category. And its property of anti-frigidity is the worst.(5)According to the above comprehensive analysis of the environmental effects of the 15 kinds of common road green tree species, the following conclusion can be reached. Lorpetalum chinense enjoys the best overall evalution so that it can be the main arbor species for Nanjing's road planting. Platanus hispanica, Ligustrun quihoui and Fatsia japonica have the outstanding performance in a certain aspect so that they can be the ideal planting trees for the road green as well. Since the Maqnolia grandiflora, Osmanthus fragrans, Populus Canadensis, Pittosporum tobira, Buxus sinica can form the beautiful landscape; they can be planted as the common trees for the road green space. However, Cinnamomum camphora, Ligustrum Lucidum Ait, Ginkgo biloba, Acer palmatum, Aucuba japonica.Var. variegate and Viburnum aabuki are lack of some extraordinary performance in any aspect. Neither the growth adaptability nor the absorbing pollution ability is good. These plants are not suitable for ornament either. Therefore, they can not meet the multi-function demands for the road green space. As the complement trees for Nanjing's road green, they can only be planted in a small number.