Analysis On Characteristics Of Roadside Trees In Wuhan,Nanchang And Changsha

As an important part of the urban green space system,street trees play an irreplaceable role in the lives of urban residents.Quickly and accurately grasp the structural characteristics and health status of urban street trees,which is conducive to the construction and management of urban forests,thereby enhancing its ecological service functions.Based on the Baidu Street View platform,this research uses the Street View tree test method to conduct a network survey of street trees in the main cities of Wuhan,Nanchang,and Changsha in the middle reaches of the Yangtze River.A total of 2828 sample plots and 66498 street trees were investigated.Our measurement indexes includ:Size indexes(Tree height(TH),Diameter at breast height(DBH),Under-branch height(UBH)and Crown width(CS)),Health indexes(Stent ratio,Dieback ratio,Unhealthy leaf color ratio,and Death ratio)and Vertical structure grade of vegetation.In addition,we studied the spatial distribution characteristics of road trees in different administrative regions and different urbanization intensities(urban-rural gradient under the development of ring roads),and explored the complex relationship between social road development factors,geographical factors and characteristics of roadside trees.The relevant results are Provide basic data and suggestions for the management of urban street trees.The main conclusions of this paper include:1.The size,health and vertical structure of street trees.Wuhan,Nanchang,and Changsha are dominated by small trees,but there are significant differences in the size of street trees in different cities.The street trees in Changsha are generally larger,and the street trees in Nanchang are generally smaller.Compared with the other two cities,The DBH of Changsha is 4～5.5 cm larger than that of the two cities,the UBH is 14～51 cm,the TH is 122～201 cm,and the CS is 155～164 cm.The health status of roadside trees in Nanchang is better than that of Wuhan and Changsha.Although there are significant differences in different areas within the city,they are all at a lower level.In addition,the health status of the leaves on the streets of Wuhan and Nanchang is more prominent,reaching 37%and 65%respectively.The vertical structure of urban vegetation is dominated by arbor-shrub-grass.The proportion of Changsha is the lowest,but it is also over 50%.The proportion of bare land in Changsha is relatively large,reaching 15%,which is 4-5 times that of the other two cities.In terms of tree growth,the proportion of street trees in Nanchang with weaker growth is higher,at 44.63%,which is 1.7 times that of Wuhan City and 3 times that of Changsha City.2.Spatial distribution characteristics of street tree structure and health.The spatial distribution of each index shows a consistent gradient change law.From the urban-rural junction to the city center,the individual street trees show an increasing trend,while the vertical structure is gradually simplified.This change has reached a significant level of difference,but the level of difference is different.As far as the vertical structure is concerned,the difference between the inner and outer rings of Wuhan is 1.2 levels,the difference between the inner and outer rings of Nanchang is 0.9 levels,and the difference between the inner and outer rings of Changsha is 1.8 levels.The overall health of forest stands in the three cities is relatively good.Although there are differences among the administrative regions and ringroad,the overall health is at a relatively low level.Almost every city’s outer ring area has average or poor forest stand health.Among them,Wuhan’s outer ring area and the entire western area of Nanchang City have poorer leaf color health,and the proportion of stents in Caidian and Jiangxia districts in the outer ring area of Wuhan is relatively high.,The proportion of stents in Kaifu District of Changsha is relatively high.3.Analysis of the complex relationship between the health,the size and structure of the street trees.The three cities all show that the size of street trees and their health are mostly negatively correlated,and the higher-level Vertical structure can often increase the risk of unhealthy trees.Between different cities,the impact of vertical structure levels on the health indicators of street trees shows differences.In Wuhan City,with the increase in the level of vertical structure,there is an increasing trend in the proportion of The Stent and the Death.In Nanchang City,with the increase in the level of vertical structure,the proportion of unhealthy leaf colors and the Stent increased.However,In Changsha City,the proportion of Stent,unhealthy leaf color,Diebacks,and Death all increase with the increase of the Vertical structure level.4.Analysis of the complex relationship between street tree characteristics,vertical structure,social road development factors,and geographic factors.The total explanatory power of social road factors and geographic factors on the size,health and vertical structure of street trees is 17.3%.DBH,TH,UBH,and CS are positively correlated with traffic flow,pedestrian flow,and shop volume,but negatively correlated with street tree density,number of lanes,and green belt width,The vertical structure is the opposite relationship with the above relationship.With the increase of longitude and latitude,the proportion of Stent increased,and the proportion of diebacks and unhealthy leaves decreased.The street trees in Wuhan,Nanchang,and Changsha showed some large,small,healthy and unhealthy conditions,but in general,the changes were relatively continuous and there was no obvious difference in distribution.All factors have reached a significant level in explaining the characteristics of street trees.The use of the surrounding environmental factors directly related to the street trees is used for evaluation,which is more conducive to the management of the street trees.Finding out the most critical indicators is the basis for clarifying the reasons for urbanization and adopting more reliable measures in the future to build a more sustainable and resilient forest.Based on these simple indicators,social development factors,geographic factors,and urban forest characteristics can be comprehensively analyzed.In summary,the overall health of the street trees in the core cities of the middle reaches of the Yangtze River is good.The street trees are relatively small and have a multi-layer structure.Based on street view measurement,a more comprehensive evaluation and spatial illustration of tree size,health and vertical distribution in a large range,multiple indicators,will be more helpful to the improvement of urban forest management based on data.Provide basic data support for regional green infrastructure construction and planning and management of urban street trees.