| Presently,from the perspective of dynamic evolution,the city-clustering has become an important trend of urban development.From the objective results,some urban clusters formed by city-clustering have become the new economic growth pole,which has led to the accelerated introduction of a series of urban cluster development plans.In the meantime,the ultra-high-speed and extensive development has brought tremendous pressure on resources and environment,making China's green development increasingly important under the new normal.Then,is there a relationship between the two development paths worth exploring? Can the urban cluster construction and the expected goal of achieving green development coexist?Scholars have continuously explored the urban cluster construction and the papers on the eco-efficiency of urban clusters have gradually increased,which has provided rich theoretical and practical guidance for China's economic transformation as well as useful reference for our thesis.But something gap in extant papers need to be fufilled.First,existing research has not examined the impact of urban clusters on urban eco-efficiency.Second,the literature has not systematically combed and summarized the mechanism of urban clusters affecting urban eco-efficiency,and the relevant evidence is also missing.Third,studies have not paid enough attention to the spatial difference and spatial effects of eco-efficiency between typical urban clusters and non-typical ones.To fill the gap,we need to answer the following questions in turn: What is the current status of urban cluster development in China? What is the current state of urban eco-efficiency and is it improved? Do urban clusters have an impact on urban eco-efficiency? If impact exsits,is there any heterogeneity? If impact exsits,what about the mechanisms? Is there a new perspective to explore the spatial effects of the eco-efficiency in terms of typical urban clusters?Based on such considerations,this paper focuses on the following logic: ?Discovering the problem--analysing the problem--solving the problem? and obtains some following findings.Firstly,we employ urban clustering degree and eco-efficiency measurement to investigate the evolution of urban cluster and eco-efficiency.The main conclusions are as follows: the urban clustering degree in China is gradually increasing.And it presents a spatial trend characterized by increasing in two ways,i.e.,north to south and west to east,which shows spatial imbalance.The urban eco-efficiency has improved,and eco-efficiency of different levels has shown an upward trend.In terms of spatial distribution,the eastern cities are slightly higher than the central and western cities,and the trend of spatial agglomeration has been strengthened.Secondly,we build panel data models to examine the impact of urban clusters on urban eco-efficiency.The main conclusions are as follows: The development of urban clusters has positively promoted urban eco-efficiency.In general,for every 1% increase in clustering degree,the eco-efficiency will increase by 0.24-0.26%;the time-separated research shows that with the acceleration of China's urban clusters construction,the positive marginal effect of clustering degree on eco-efficiency is enhanced.The sub-sample studies confirm that the impact of urban clusters on urban eco-efficiency is heterogeneous.Taking the east,central and west cities as sample,we know that the improvement of the urban clustering degree in the east,central and west is conducive to the urban eco-efficiency.Over time,the positive marginal effect of urban clusters on urban eco-efficiency has been reduced slightly in east cities;the positive effect of urban clusters on urban eco-efficiency has gradually emerged in central and west cities;similarly,the core-periphery subsample can be concluded: the improved clustering degree benefits the eco-efficiency of the core and peripheral cities,but with differences.The positive effects of the core cities in urban clusters on the eco-efficiency are stronger than those in the peripheral cities.Thirdly,through theoretical analysis,mediating effect model and moderating effect model,we explore the mechanisms of urban clusters affecting urban eco-efficiency.We argue that urban cluster can enhance the urban eco-efficiency through the following three paths,i.e.,structural transformation,market integration and factor agglomeration mediation.The main conclusions are as follows:1)We first estimate the urban market integration and then with the empirical evidence,we have the following conslusions.From the overall perspective,the urban clusters have the promotion effect of market integration,which could benefit the eco-efficiency.Sub-sample research shows that in the process of urban cluster development,the central and western cities are relatively insensitive to weakening local protection and promoting market integration compared with eastern cities;the market integration response coefficient of core cities is significantly better than that of marginal cities;the market integration effect of inter-provincial urban clusters is weaker than that of urban clusters placed in one province.2)We first estimate the rationalization and supererogation of industrial structure,which can represent the transformation of industrial structure,and then with empirical evidence,we have the following conslusions.From the overall perspective,the urban clusters can drive the industrial structure transformation,which has positive influence on the urban eco-efficiency.Sub-sample research shows that the driving effect in different regions is heterogeneous,and also represents difference in economic logic.For the eastern cities,the cluster development positively affects the rationalization and supererogation of the industrial structure,and the latter two are positively related to the eco-efficiency;for the central and western cities,the clusters negatively affects the rationalization of the industrial structure,and the latter is negatively correlated with eco-efficiency;for central cities,its cluster development positively affects the industrial structure,and the latter is positively related to eco-efficiency,while the path of industrial structure supererogation in western is unstable.3)We first estimate the industrial agglomeration and population agglomeration of cities,and then with the empirical evidence,we have the following conslusions.From the overall perspective,the urban clusters has moderating effect of factor agglomeration,which is conducive to the urban eco-efficiency,and with the increase of urban clustering degree,the moderating effect has been enhanced gradually.Sub-sample studies show the factor agglomeration moderating effect is heterogeneous,which is more significant in high-density and eastern cities,while not obvious lowand medium-density cities and the central and western cities.This can not benefit the release of the complementary effects of urban factor agglomeration and urban clusters when improving the urban eco-efficiency.Compared with industrial agglomeration,the moderating effect is relatively weak when population is agglomerated.Fourthly,we employ the hot zone Yangtze River Economic Belt and use the spatial Dubin panel model to explore the spatial effect of eco-efficiency.The main conclusions are as follows: From the overall perspective,the eco-efficiency of typical urban clusters is higher than that of non-typical urban clusters,and former one has spatial effects.Sub-sample studies show that: there are spatial effects of high-value eco-efficiency on low-value eco-efficiency in different samples.The Yangtze River Delta urban cluster is dominated by positive spatial spillover(diffusion effect);the Yangtze River middle reaches urban cluster has the negative effect(siphon effect),which then change to a weak positive effect(diffusion effect);The Chengyu urban cluster has the negative effect(siphon effect).Additionally,the spatial effects of eco-efficiency of urban clusters with better development level are more significant,which has represented positive space spillover.However,the spatial effects in terms of the urban cluster that characterized with rising period is unstable,showing the coexistence of positive and negative spatial effects.Finally,based on the conclusions,several policies are proposed to optimize the urban clusters to drive the urban eco-efficiency and green development in China.Recommendations are shown below: to continuously promote urban cluster and build a complete urban cluster system;to enhance favorable conditions for strengthening the mechanisms of eco-efficiency growth effect;to take spatial effects seriously,and build a synergistic improvement pattern of eco-efficiency. |
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