| Urban green space is an important carrier of urban ecosystem,and its ecological function has an irreplaceable role in the sustainable development of modern society and the improvement of residents’ quality of life.In today’s society where urban land is expanding drastically and urbanization is developing rapidly,how to give full play to the ecological functions of urban green space system is the top priority for achieving sustainable urban development.Therefore,the construction of a reasonable comprehensive evaluation system is a pointer for the development of urban green space system,which can be analyzed for targeted evaluation and effectively guarantee the ecological function of green space system.As the capital of Jiangxi Province,Nanchang is an inter-provincial transportation corridor connecting three important economic zones(Yangtze River Delta,Pearl River Delta and Economic Zone on the West Coast of the Strait).Nowadays,with the rapid expansion of construction land,problems such as urban landscape fragmentation and ecological land reduction have emerged.It is important to analyze and evaluate the urban green space system in the central urban area of Nanchang to objectively identify the problems and shortcomings in the construction of the green space system for the future sustainable development of Nanchang.This paper takes the central urban area of Nanchang as the study area,based on the three phases of remote sensing image data,DEM data and basic data such as road network in 2000,2010 and 2020,and on the basis of analyzing the evolution of landscape pattern in the central urban area of Nanchang and constructing a network analysis model for green space system accessibility evaluation,it constructs a green space system in terms of green space quantification,patch type,landscape level and landscape structure,etc.Based on the results of the evaluation system,a comprehensive evaluation system for the green space system in the study area was constructed,and strategies were proposed for the optimization of the green space system in the central city of Nanchang based on the results of the evaluation system.The main conclusions are as follows:(1)The two most dominant landscapes in Nanchang are the cropland landscape and the built-up land landscape,which are also the two landscape types with the largest fluctuations during the study period.2000-2020 saw a decline in the cropland landscape,which is the dominant landscape in the study area,with a total decrease of over 11,000 hectares of cropland over the two decades.At the same time,the rapid economic development of Nanchang between 2000 and 2020 saw the landscape of built-up land rise year by year,with the largest fluctuation range as the landscape area increased by more than 13,900 hectares.Water landscapes,woodland landscapes and other landscapes show the opposite trend to construction landscapes,with an overall decrease from 2000 to 2020.The results of the landscape spatial transfer matrix show that the outflow type is dominated by arable land,woodland,water and other land,and the inflow type is dominated by construction land,indicating that the expansion of construction land is mainly from the development of large amounts of arable land.The analysis of the landscape pattern index shows that the landscape shape index and landscape separation have been increasing in Nanchang,and the landscape spread and aggregation have decreased,indicating that the landscape shape has become more irregular and complex during this period,and the degree of landscape fragmentation has increased.(2)From the perspective of urban green space green volume index,although the number of green spaces in the central city of Nanchang is large,they are mostly scattered small blocks and strips of green space patches,and the per capital green space area is far from meeting the needs of the city.From the overall layout of the green space system,the construction of park green spaces in the central urban area of Nanchang is relatively concentrated and uniform,but the park green spaces are mostly gathered in the core of development,densely populated areas or near river resources with rich water systems,thus leading to uneven spatial distribution,and some areas are still not covered by green space services.Combined with the accessibility analysis,it is found that the density of green spots around the core areas of urban areas is higher,the road traffic network is more complete,and the accessibility of corresponding green spaces is better.However,large integrated parks are basically built in the south and west of the study area,and residents need long transportation costs to reach them,so it is important to strengthen the convenience of the public transportation network to improve the travel speed of urban residents and the accessibility of park green spaces.(3)Based on the review of literature and the actual situation of local residents’ community life circle construction,this paper divides the accessibility into three different types of transportation modes: walking,bicycling and motor vehicle traffic,and uses the length of travel time as a more accurate and intuitive measure of local residents’ accessibility to park green spaces.The results of the analysis show that there is a medium preference for the accessibility of parkland in the central city of Nanchang.(1)Under the walking mode,the accessibility of urban parkland is poor,and the service area is mainly concentrated in the green areas that exist in the central city in the form of points,or in patches of green areas along the Ganjiang river system.The areas far from the city center cover a relatively small area.The number of green areas in parks should be increased in an appropriate amount to improve the density of green spots in each administrative district and to ensure that more citizens can reach green areas by walking.(2)With cycling,the accessibility of urban parks and green spaces increases significantly,with more than half of the population being able to reach the parks and green spaces within 20 minutes,but the accessibility is relatively concentrated in the densely populated central areas.(3)The service coverage is the most extensive and the accessibility is the best under the mode of transport of motorized travel,with more than 80% of the service area of parks accessible within 15 minutes.However,on balance,motorized travel is not only more costly in terms of travel expenses,but also does not comply with the environmental protection policy of green travel.Visitors tend to choose to use this mode of transport on weekends or holidays,thus invariably adding to the pressure on the urban environment,traffic,time spent on travel,etc.Therefore,this mode can only provide a certain reference for accessibility,and frequent use of motor vehicles is not recommended for travel under various considerations.(4)Based on the above analysis,the comprehensive evaluation result value of the green space system in the central city of Nanchang is 7.231,which is in level II from the evaluation score classification,indicating that the current urban green space system construction is in general preference and there is room for further optimization.Based on the evaluation system,we propose optimization strategies for the green volume,function and layout of the green space system based on the actual problems of the green space system construction,so that the green space system can better perform its service functions.To improve the green quantity and green quality of urban areas;to improve the road traffic network and increase the accessibility of green areas;to enhance the coherence of the park green area system and optimize the spatial layout of green areas;to improve the satisfaction of park green areas by combining the needs of residents;to optimize the green area system and build an urban green ring. |
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