Quantitative Analysis And Optimization Of Eco-spatial Structure In A High-density City

It has been well acknowledged that a sound ecological environment is the most equitable public product and the most inclusive well-being of the people.With the acceleration of urbanization and the growth of urban scale,ecological green space is eroded by the increasingly expanding construction.This brings considerable negative effects to human society,including the fragmentation of urban ecological land,the loss of biodiversity,and the decline of the quality of ecological space.Focusing on the reconstruction of the spatial planning system,the optimization of the development and protection pattern of the land space,as well as the promotion of the modernization of the land space governance capability,the government is making efforts to improve the quality and stability of the urban ecosystem.As the ground public open space,a reasonable and orderly structure of urban ecological space is taken as the natural basis and ecological guarantee for urban survival and development.Through research on urban ecological spatial structure,it is expected to achieve the construction of urban natural ecosystem and the maintenance of urban ecological spatial pattern.In theory,by bringing human factors into the category of traditional ecological space research and combining with the particularity of high-density cities,the conceptual framework,logic line and key points of ecological spatial structure are systematically proposed.In this way,the conceptual system and technical methods of urban ecological spatial structure shall be expanded.In practice,existing problems in urban ecological spatial structure are examined and diagnosed from multiple dimensions.While contributing to the adaptive optimization and integration of urban ecological space,this will provide reference for the improvement of the ecological space governance capacity of other cities.As a representative of the dramatic urbanization in China and even the world,despite limited space resources,Shenzhen accommodates a large population and therefore presents a pattern of high-density development in spatial form.Taking Shenzhen as the research area,this paper adopts system ecology and graph theory as theoretical guidance,with comprehensive application of interdisciplinary knowledge including ecological process,source & sink principle,complex network,spatial analysis,big data and computer simulation.The modeling,analysis simulation and optimization of Shenzhen’s ecological spatial structure is conducted based on three major issues,namely "building the ecological spatial structure model of high-density city","quantitative analysis of the hierarchical relationship,organizational mode and anti-destruction ability of the ecological spatial structure",and "optimization path of the ecological spatial structure coupled with technology and policy".The results are of practical significance for the maintenance of urban ecological security,the allocation of spatial elements and the optimization of land layout.In this paper,there are different insights and innovations in the concept model of urban "nature-society-system" ecological space,quantitative diagnosis method of network structure and technical scheme of structural optimization.The main research contents are as follows:(1)Analysis of the characteristics and the construction of the conceptual framwork of the ecological spatial structure of high-density citiesFollowed by a systematic review of theories related to urban ecological space,network and complex scientific theory,urban ecological system is considered to be a ternary system including "natural system,semi-natural system and social system" based on the understanding of the heterogeneity and functional compounding of high-density urban space.This suggests the necessity of integrating "natural service" and "social service" in spatial structure.Hence,the concept model of ecological spatial structure is constructed,and the overall research framework and key points of high-density urban ecological spatial structure are put forward.The main technical schemes,such as structural element extraction,community structure development,stability simulation and structure optimization simulation,are then proposed.(2)Modeling and Element identification of ecological spatial structureThe ecological process scenario is set in accordance with the understanding of the characteristics of high-density cities.The "patch-corridor" functional structure is constructed based on the ecological process by adopting the shortest path algorithm of grid resistance surface.Through the setting of humanistic process scenarios and the introduction of mobile signaling data,the construction of supply and demand service structure is built.According to the defined structural semantic model,the patch structure is composed of the source and the connection between sources,which are not directional and are entitled to make edge connection;Composed of recreational service supply nodes,residential demand nodes and their connection paths,the supply and demand structure is directional and is as well entitled of edge connection.(3)Quantitative evaluation and problem diagnosis of ecological spatial structureBy introducing quantitative ecological analysis,the framework of urban ecological spatial structure analysis is explored from different perspectives,namely structural hierarchy(micro),structural agglomeration(meso)and structural stability(macro).At the micro level,the assessment of structural hierarchy is carried out with nodes as the objects,while the significance and primacy of nodes are divided to reveal the problems of low connectivity and patch isolation.At the meso level,the local relations between nodes and edges are taken as objects to conduct key evaluation of the local clustering characteristics of nodes.The community structure of the portico structure and the supply and demand service structure is explored,so as to analyze the spatial organization mode of the structure.At the macro level,the structural stability is emphatically evaluated with the network formed by nodes and edges as the objects.The threshold and failure spatial distribution of nodes that lead to network collapse are then discussed.(4)Optimization technology and implementation strategy of ecological spatial structureWith management oriented application as the goal,in view of the analysis of problems in the ecological spatial structure,the technical path of ecological spatial optimization is explored on the one hand.It is proposed to improve the connectivity and stability of the portico structure,as well as the balance and stability of the supply and demand service structure.On the other hand,oriented by governance,Based on the space boundary and policy landing,policies suitable for spatial and usage control is then put forward by combining the scenarios in reality and planning.The main conclusions of this paper are:(1)The "patch-corridor" structure based on ecological process and the "supply benefit" service structure based on human process are constructed by setting two types of "flow space" scenarios.Model semantics include node,edge,weight,directionality,etc.(2)The structure of ecological space demonstrates certain hierarchical characteristics.The node hierarchy feature of the supply and demand structure is more significant on the whole.The distribution of high-level nodes tends to be neutral.The adjacent relationship of spatial nodes in edge areas is extremely weak.(3)The ecological spatial structure shows the characteristics of community structure.11 communities of portico network and 16 communities of supply and demand service network(including one super-large community)are explored,which assume distinct local clustering feature with an modularity greater than 0.5.Thus it can be seen that the boundary of communities is obviously.(4)On the whole,the ecological spatial structure is relatively stable.In the selected attack simulation scenario,the performance of the network shall be halved when the node proportion is removed by about 30%.At this point,the network structure in the middle of the research area is important but be vulnerable to serious damage.(5)Point and edge increase is believed one of the optimization strategies suitable for the area,such as planning strategies of rebuilding the existing green space resources and increasing small and medium-sized recreational space.(6)The nearest distance criterion and the priority connection criterion are proposed through the local evolution model.After optimization,the connectivity of the portico network increases by 15% and the Gini coefficient of the supply and demand service network decreases by 24%,indicating the improvement of the survivability threshold of both.