| Urban agglomeration is the main form of China's current development,but its development is also a process of resource consumption.China is in an important stage,which is characterized by rapid urbanization,sustained industrialization and economic and social transformation.However,the time-lag of urban development planning and the extensive development mode of exchanging resource consumption for economic expansion in the early years have destroyed the space-time development order of the natural ecological environment,thus posing a threat to the living environment of human beings.Therefore,in the development process of urban agglomeration and its spatial network,ecological security should be taken into account.In essence,the polycentric evolution of urban agglomeration spatial network can be regarded as a process of order change caused by the spatial interaction of urban elements.Elements in urban agglomeration may interact with each other in the form of material,energy and information flow.Various "factor flows" will be associated with different spatial units,resulting in corresponding changes in the network structure and spatial organization pattern of urban agglomeration,forming a polycentric network development trend.The research on the formation mechanism of this polycentric process can not only enrich the theory of urban agglomeration development,but also help to provide decision-making basis for regional comprehensive governance.Taking the urban agglomeration around Poyang Lake as a case study,this paper constructs the analyzed framework through the "pattern identification-process analysis-mechanism study",so as to provide a new perspective and methodological basis for the study on the polycentric evolution of urban agglomeration spatial network.On the basis of the literature review at domestic and abroad,the relevant concepts are identified and their theoretical relationships are analyzed,and the analytical framework of the paper is proposed.Secondly,taking ecological security as the relaxation constraint,semantic analysis,morphological spatial pattern analysis,landscape connectivity and elasticity analysis were applied to identify the constraint pattern of ecological security.Thirdly,according to the the development stage of the research area,the industrial network and information network are selected as the representative elements of agglomeration and externality,and the "global agglomeration degree-intensity of industrial flow" model and the "SNA-gravity model" are constructed respectively to identify the polycentric pattern of the industrial network and information network in the research area.Fourthly,the complex ecosystem theory is used to integrate ecological security,industrial network and information network,and the mechanism of polycentric evolution of spatial network around Poyang Lake urban agglomeration is obtained.The research conclusions are as follows :(1)During 2000-2015,the connectivity of ecological sources around Poyang Lake urban agglomeration has gradually decreased,and the connectivity at the end of the study period can be divided into three levels according to their importance: "absolutely prohibited development","strictly restricted development" and "conditional development".The reduction rate of ecological source AREA(Area)slowed down,but the corresponding loss rate of ecological service value(ESV)did not decrease.The occupied ecological source areas have greater elasticity to GDP and fixed asset investment,but no obvious elasticity to population index.This is mainly because the development of the study area is dominated by urban infrastructure,and it is currently in the initial stage of urban agglomeration development.(2)It is found that the industrial network around Poyang Lake urban agglomeration during the study period is supported by labor-intensive and resource-intensive industries,and then shifted to a development mode of labor-intensive and resource-intensive industries,and technology-intensive industries as the leading industries.In terms of spatial distribution,the urban districts are the industrial centers,while the periphery areas with strong industrial flow show the potential to grow into the secondary centers.In terms of structural change,the long-term coexistence of competition and cooperation between Nanchang and Jiujiang leads to the intersecting of the hinterlands of the two cities and the obvious tendency of backward development.The emergence of other secondary centers reduces the compactiveness of urban agglomerations and increases the degree of equilibrium,thus leading to the structural evolution from dual-core to multi-center.(3)From 2000 to 2015,the information network around Poyang Lake showed a polycentric evolution pattern,with Nanchang City as the most important node,and the secondary centers began to develop.Specifically,in the study period,the number of intercorrelations among cities increased significantly,and the connections within urban agglomerations became increasingly close.However,from the perspective of centrality,the jurisdiction of Nanchang always occupied an important position in the network.From the perspective of hierarchical structure,the hierarchical structure of urban agglomeration network around Poyang Lake is relatively simple,with only a few cities in the information block group.From the perspective of network heterogeneity change,the scale-free attribute value ? of the information network around Poyang Lake has been greater than 1 since 2010,indicating that the network began to evolve into a polycentric network.(4)The driving factors of industrial network evolution in the Poyang Lake urban agglomeration under the constraint of ecological security are discussed.On the macroscopic urban level,the formation mechanism of external economic connection and spatial agglomeration between cities is discussed.It is found that under the constraint of ecological security,the outward function between cities expands,and the industrial flow between cities is formed under the action of spatial spillover effect.At the micro enterprise level,the formation mechanism of industrial agglomeration within the city under the constraint of ecological security is discussed by focusing on the site selection behavior within the agglomeration circle.It is found that under the slack constraints of ecological security,enterprises choose to move into the existing industrial agglomeration circle or the location of adjacent similar enterprises mainly for the consideration of their own financing costs,and the location behavior of enterprises is actually a manifestation of the division of industrial value,which gradually induces the formation of economic production center.Therefore,the correlation creation between cities on the macro level and the superposition and compound of economic production centers on the micro level form a polycentric industrial space network around Poyang Lake urban agglomaration.(5)In the context of ecological security,the essential core of information network is the ability to provide basic public services to the society.The three aspects of urban function distribution,urban competition and cooperation relationship and ecological security objective constraint are the evolution pattern that promotes the polycentric development layout of basic public services in the form of information network.(6)Taking the industrial network of the urban agglomeration as the economic subsystem,the information network as the social subsystem,and the ecological security constraint as the representative of the natural subsystem,the Poyang Lake urban agglomeration composite ecosystem was constructed.The driving factors of polycentric evolution of urban agglomeration spatial network and the relationship among three subsystems constitute the mechanism of polycentric evolution under the constraint of ecological security.The innovation points of this study are as follows :(1)Taking ecological security constraints as a bottom-line perspective,the study proposes a new view and method to identify regional ecological security constraints based on the connectivity and intertemporal changes of ecological sources,thus realizing the multi-dimensional connotation unification of the same concept.(2)Taking ecological security,industrial network and information network as interaction subsystems,the concept and analyzed framework of complex ecosystem for the evolution of spatial network of urban agglomerations in the lake region are proposed,which provides a new perspective and technical route for the research on the evolution of spatial network of urban agglomerations.(3)in combination with the study area's stage of development,the selection of industrial network and information network as the agglomeration and externality representative elements,respectively,to build "DO index-industry flow intensity" model and "SNA-gravity model" to identify the study area industry network and information network center model,thus providing methodology basis for urban agglomeration spatial network model. |
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