| Since the reform and opening up,China’s economy and society have developed rapidly,and world-renowned achievements have been made,with the acceleration of industrialization and urbanization.However,the extensive mode of economic development enlarges economic aggregate at the cost of consuming a multitude of resources as well as causing serious environmental pollution,leading to regional resources and environmental carrying capacity decline.As an important economic development corridor in the national development strategy,the Yangtze River Economic Belt has established a development orientation led by ecological priority and green development,and has achieved good results in ecological civilization construction.However,there are still bottlenecks to achieve its high-quality development.The large gap among the development of the upper,middle and lower reaches of the region,the uncoordinated economic spatial layout and industrial structure of the region,the poor cross-regional flow of resource factors,and the aggravating pressure on ecosystem conservation and restoration are multiple factors that restrict it from creating a strategic engine to promote the national economy.As the Yangtze River Economic Belt is a national demonstration zone for ecological development,it is important to study the spatial correlation network pattern and formation mechanism of urban eco-efficiency in the region to optimize economic spatial layout and upgrade quality and efficiency,strengthen ecological civilization construction and regional coordination and innovation for high-quality development.This paper measures the urban eco-efficiency of the Yangtze River Economic Belt based on the non-expected output SBM model,constructs the spatial correlation network of urban eco-efficiency of the Yangtze River Economic Belt using the modified gravity model,and then uses the social network analysis method to further explore the structural characteristics and evolution trend of the spatial correlation network of urban eco-efficiency of the Yangtze River Economic Belt.Meanwhile,based on QAP model to explore the formation mechanism of the spatial correlation network of urban ecoefficiency in the Yangtze River Economic Belt.The study results are as follows.（1）The spatial distribution of urban eco-efficiency in the Yangtze River Economic Belt is extremely unbalanced,with high-efficiency areas being scattered and varying widely;in general,urban eco-efficiency in the middle and lower reaches is higher than that in the upper reaches,and low-efficiency cities are mainly distributed in the upper reaches.From 2005 to 2019,the overall urban eco-efficiency of the Yangtze River Economic Zone showed a fluctuating upward trend,and the growth rate showed the evolutionary characteristics of "fast-slow-fast",and the urban eco-efficiency showed a rapid growth at low level from 2005 to 2009,a fluctuating and stable growth from 2009 to 2014,and a high-efficiency and fast growth from 2014 to 2019.（2）The overall spatial correlation network of eco-efficiency in the Yangtze River Economic Zone has the structural characteristics of "dense downstream,scattering middle reaches and sparse upstream".The downstream Yangtze River Delta regional sub-network is radially concentrated and relatively compact,forming a stable "diamond structure".In the midstream region,Wuhan and Changsha are the cores of the regional sub-network,and the overall network structure is relatively decentralized.The spatially linked network in the upstream region is sparse except for the Chengdu-Chongqing urban agglomeration.The spatial correlation intensity of urban eco-efficiency in the Yangtze River Economic Belt ascends yearly,with increasingly significant coordinated development and spillover effects,and gradually breaks the previous spatial network structure of strict hierarchy,and the number of relationships of spatial correlation of eco-efficiency among cities gradually increases,enhancing the stability of the spatial network structure.（3）The centrality of urban nodes in the Yangtze River Economic Belt shows obvious unbalanced characteristics in space,but the regional differences are gradually reduced over time.The central cities in the region,represented by Shanghai and Chongqing,are the main radiation poles of the Yangtze River Economic Belt,driving the eco-efficiency of the surrounding cities.The Yangtze River Delta region has always been the core of the spatial correlation network of urban eco-efficiency in the Yangtze River Economic Belt,and has strong control with other central cities in the region,determining the evolution of the spatial correlation network of eco-efficiency.（4）The core area of the urban eco-efficiency spatial linkage network in the Yangtze River Economic Belt has been expanding,and gradually breaks geographical restrictions and shows a concentrated development trend.The eco-efficiency spatial association is mainly concentrated within the core area,and between the core area and the peripheral area,with less connection within the peripheral area.The strength of spatial association between cities in the core area has been increasing over time,promoting the optimization of the overall network structure.However,the cities in the peripheral area always maintain weak connections,hindering the development of spatially linked networks.（5）There are obvious characteristics of plate change of the spatially linked network of urban eco-efficiency in the Yangtze River Economic Zone,with significant differences in links between different plates,and the members of the plates develop from clustering in spatially adjacent areas to clustering with cities at similar economic development,and the spatial links within and between the plates increase over time.（6）The regression coefficients of the matrices of geospatial proximity,and differences in economic development,opening-up and labor force size are significantly positive,indicating that the larger their differences,the more they promote the formation of eco-efficient spatial linkage networks in the Yangtze River Economic Belt.The regression coefficients of the matrices of differences in technological and transportation development are significantly negative,indicating that the more similar they are,the more they can promote the formation of eco-efficiency spatial association network in the Yangtze River Economic Belt. |
