Quantitative Analysis Of Ecological Benefits On Common Street Trees In The Guanzhong Area

With the large-scale development of urbanization in China,the problem of urban road greening is increasingly fragile.As an important part of street greening,Urban street trees can release oxygen,fix carbon,drop temperature effect,add humidity effect,absorb dirt,kill germ,decrease nose and release air anion effect to modulate the micro-climate,contrast the urban heat island effect,improve the comfort of pedestrians,create a pleasant space environment and at the same time improve the quality of the sidewalk environment.Therefore,choosing appropriate trees has great significance for our city.However,by analyzing the present condition of road greening of our country,road forestation has been more focused on aesthetic and crash feeling,and neglect the ecological benefits of street trees.The paper aims to ecological benefits system of street trees suitable for local characteristics to provide guidance about street trees selection.In recent years,single ecological function of street trees has flourished.However,there are few on comprehensive index.Thus,this paper focus solely on the quantitative research and evaluation system of common street trees in Guanzhong area.This paper takes Xi'an and Yangling as representative cities in the Guanzhong region.Meantime through the measurement analysis of the green quantity,carbon fixation and oxygen release,temperature reduction and humidification,negative oxygen ion concentration,and dust retention effects of 15 street trees,the index weight is obtained.On this basis,the comprehensive ecological benefits of 15 street trees is evaluated and marked.After this we analyze and summarize the different level species of street trees in Guanzhong region.Finally,we get the cological benefit evaluation grade table of street tree species.Main results for this study are as follows:1)The differences of the canopy structure,leaf area,distribution density of different street tree species have caused their leaf area index(LAI)to vary.The leaf area index(LAI)of street tree species are ranked as follows: Magnolia grandiflora >Platanus orientalis > Ginkgo biloba > Osmanthus fragrans > Catalpa bungei >Aesculus chinensis > Magnolia denudata > Ligustrum lucidum > Cedrus deodara >Acer mono > Ailanthus altissima > Melia azedarach > Sophora japonica >Koelreuteria paniculata > Pinus tabuliformis;Their green quantities are ranked as follows: Platanus orientalis > Melia azedarach > Sophora japonica > Cedrusdeodara > Magnolia grandiflora > Acer mono > Koelreuteria paniculata > Aesculus chinensis > Magnolia denudata > Ligustrum lucidum > Catalpa bungei > Ailanthus altissima > Pinus tabuliformis > Ginkgo biloba > Osmanthus fragrans.2)With the aid of on-the-spot investigation,the paper analyze the relationship between growth parameter and leaf area index of 15 street trees in Guanzhong area and at the same time build the related functions.Experimental results show the strongly positive relationship between chest circumference,tree height,crown diameter and green quantity.That is to say,the green quantity increased with the increase of chest circumference,tree height whithin limits.3)By analyzing the data of photosynthetic rate,the seasonal variation of photosynthetic rate of 15 street trees is ranked as follows: summer > spring > autumn >winter.And the annual average fixing carbon and releasing oxygen is ranked as follows:Platanus orientalis > Magnolia grandiflora > Cedrus deodara > Ligustrum lucidum >Melia azedarach > Sophora japonica > Koelreuteria paniculata > Magnolia denudata > Acer mono > Pinus tabuliformis > Catalpa bungei > Osmanthus fragrans > Aesculus chinensis > Ailanthus altissima > Ginkgo biloba.4)Daytime change of transpiration rate of trees bring into correspondence with the photosynthetic rate.The average cooling and humidification effect is ranked as follows: Platanus orientalis > Melia azedarach > Sophora japonica > Koelreuteria paniculata > Cedrus deodara > Acer mono > Magnolia grandiflora > Ligustrum lucidum > Magnolia denudata > Aesculus chinensis > Pinus tabuliformis > Ailanthus altissima > Catalpa bungei > Ginkgo biloba > Osmanthus fragrans.5)Due to the frequent rainfall in guanzhong area,there is usually no more than three weeks of dust retention.The total dust retention of a single plant during the dust retention period is ranked as follows: Platanus orientalis > Cedrus deodara >Magnolia grandiflora > Sophora japonica > Melia azedarach > Ligustrum lucidum >Koelreuteria paniculata > Acer mono > Pinus tabuliformis > Catalpa bungei >Magnolia denudata > Ailanthus altissima > Aesculus chinensis > Ginkgo biloba >Osmanthus fragrans.6)The ability of different tree species to provide air anion was significantly different.Their negative oxygen ion concentration is ranked as follows: Koelreuteria paniculata > Ginkgo biloba >Magnolia denudata > Sophora japonica > Ailanthus altissima > Acer mono > Platanus orientalis > Aesculus chinensis > Catalpa bungei >Melia azedarach.7)according to the comparative scoring of the indicator layer by experts and insiders,the weights of the indicators are evaluated and scored.The five impact factor weights are ranked as follows: green quantity>dust retention effects>carbon fixation and oxygen release(temperature reduction and humidification)>negative oxygen ion concentration.Meantime,Based on the actual measurement analysis above,the ecological benefit evaluation ranking table of 15 street trees was finally obtained.The trees which have excellent ecological benefits include Platanus orientalis.The trees which have great ecological benefits include Cedrus deodara,Sophora japonica,Magnolia grandiflora,Melia azedarach.The trees which have general ecological benefits include Acer mono,Ligustrum lucidum,Magnolia denudata,Pinus tabuliformis,Aesculus chinensis,Catalpa bungei,Koelreuteria paniculata.The trees which have worse ecological benefits include Osmanthus fragrans,Ailanthus altissima,Ginkgo biloba.Proceed from climate of Guanzhong area,this paper explores a systematic index system for evaluating the ecological benefits of urban street trees,and at the same time build a ranking table of ecological benefits for street trees.This paper aims to provide important scientific basis for the selection and evaluation of urban street trees in Guanzhong area.