Species Composition And Vertical Structure Of Urban Roadside Trees In Main Cities Of China

Urban environment deterioration in China requests urban vegetation(mainly composed by urban forest and tree)exerting larger ecological service,while one basis for policy makers is an overall,exact and efficient evaluation of urban forests both inter-cities level and different districts within a city.The popularization of urban street scene big data provides a new method for rapid,large-scale and wide-area urban vegetation survey.Previous studies were mostly located in a single city or region,and it was difficult to reveal its general rule.We selected China's 35 major cities,with a total of 88632 plots by using Baidu Street View(BSV).The tree species composition,relative abundance and vertical structure were investigated.Based on this,the paper analyzed the characteristic differences of forest trees in different cities and regions(Northern,Southern,Qinghai-Tibet and Northwestern cities),compares the literatures,and puts forward some suggestions.The preliminary conclusions are as follows:(1)There were 99 street trees commonly used in the 35 cities based on the street BSV survey.The most common tree species were Populus spp.,Salix spp.,Cinnamomum camphora,Pinaceae,and Sophora japonica.Only Kunming and Guilin street species configuration were reasonable at species level according to the 10/20/30 "rule of thumb".In particular,the relative abundance of Populus spp.was as high as 61.2%,in Karamay.The proportion of Cinnamomum camphor a trees exceeds 50%of the total number of tree species in Changsha and Hangzhou.The primary reason was that single-species occupy absolute predominance which made the relative abundance ratio of other tree species less or even no.(2)Most of the street trees in Southern cities are broad-leaved trees e.g.,Cinnamomum camphora,while in Northern and Northwestern cities,Populus spp.,Salix spp.and Sophora japonica were dominant,and in the Qinghai-Tibet area,Populus spp.and conifer were dominant.In the four areas,the dominance of single species was obvious,more than 23%,street tree configuration was unreasonable at the species level.The study on the composition of main tree species in the city had little difference with that in the past.All cities was reached consistency,and only 8 cities were not ideal(fair consistency).In terms of tree species relative abundance,this study filled the blank of species relative abundance in 22 cities.This paper also expanded the research scope and samples of 13 cities,making the data more reliable.(3)There was no significant difference in the vertical structure of 35 cities,and in most cities the proportion of arbor,shrub and grass three-layer combinations was much higher than others.In the geographical area,the proportion of the three-layer structure of urban was higher than that of other combinations in the region,all of which exceed 45%.There was little difference in the overall score of arbor,shrub and grass three-layer combinations,which showed homology.Grassland desert was different from the Climatic top-level vegetation structure.The proportion of shrub structure was relatively low,no more than 0.7%.Therefore,the planting of shrub should be increased in each region,and reduced bare land,so as to build a low-cost and efficient greening program based on nature.Our results supplement the previous data of tree species composition,relative abundance and vertical structure,and provide important parameters for the national planning of urban forests and the comprehensive improvement of ecological services function.