| China's urban agglomerations,as an emerging regional unit upon which the country has heavily relied to participate in global competition and international division of labor,are the growth poles of regional economic development in the future.The country has thereby issued a series of related plans.The National Plan for Development Priority Zones specifies that urban agglomerations are the key areas and priority zones for implementing development,and the National Plan on New Urbanization Plan specifies that urban agglomerations are the main form of promoting new urbanization.Compared with urban areas,urban agglomerations are a gathering place for urban land expansion.The continuous high-intensity and extensive land development has put tremendous pressure on the resource allocation and environmental carrying capacity of urban agglomeration areas,making high-quality development of urban agglomerations under modern national space governance increasingly important.Therefore,development of urban agglomerations should be corporated with ecological protection to simulate different scenarios of urban land expansion,scientifically delineate the growth boundary of urban agglomerations,and formulate corresponding management and control models.As a result,a comprehensive growth boundary management system will be formed.This is to optimize the land space of urban agglomerations,an effectiveway to ensure the quality development of urban agglomerations,and in the meantime a theoretical reference for the integration and sustainable development of urban agglomerations.Based on socio-economic,land-use coverage,basic geography and other types of data,methodolodies like urban land expansion intensity,landscape expansion index,multiple linear regression,system dynamics,cellular automaton were utilized comprehensively,with Changsha-Zhuzhou-Xiangtan(CZT)urban agglomeration as the research object.Aspects of research included the spatial and temporal characteristics of urban land expansion,the quality of expansion,the symbiotic mechanism of urban land expansion and eco-environmental protection,simulation of expansion,and delineation of growth boundaries in the urban agglomeration.These have been studied comprehensively and systematically to solve three key scientific issues:(1)exploring the influencing factors and mechanism of urban land expansion in the urban agglomeration;(2)studying the interaction and the balance point of coordination and co-existence between the development of urban agglomeration and ecological protection under the coordinated symbiosis model of "production-life-ecology" in the urban agglomeration;(3)researching and establishing a coupling model to eliminate the conflict between urban development and ecological protection,and simulating different growth scenarios by combining ecological constraints andgrowth demand as well as exploring methods of delineation in growth boundary of the urban agglomeration based on its development goals and regional functions.In accordance with the research idea of ??“characteristic analysis-scenario simulation-boundary delineation-optimization control”,this paper conducted qualitative and quantitative analysis on the expansion of urban land in the urban agglomeration and its optimization control,and the main results found:(1)There is a strong difference in the urban land expansion of the CZT urban agglomeration at different development phases.In terms of temporal intensity changes,the expansion intensity of urban land in the urban agglomeration increased in the beginning and then decreased.In terms of spatial pattern evolution,it presented a “center-periphery”expansion pattern.The type of expansion as a whole was changing from diffusion to agglomeration,which is in line with the“diffusion-agglomeration” urban growth theory.The enclave-type expansion was the dominant type from 1995 to 2010,while between 2010 and 2018 the marginal expansion type replaced the enclave type as the leading one.Regarding the quality of urban land expansion,as the urban land expanded and engulfed the suburbs and rural areas,the landscape fragmentation and its shape complexity continued to rise with the landscape pattern indicating instability.In addition,the degree ofpopulation-land synergy in this urban agglomeration was enhanced gradually,and the overall degree of economic-land synergy was rather high,which implies that the quality of urban land expansion has improved.(2)There was a strong interaction between urban land expansion and ecological environmental protection in the urban agglomeration,and the intensity of each element's action between the two systems exhibited different characteristics in different stages.Also,the drive-coordination-restriction symbiosis mechanism based respectively on the three dimensions of nature,social economic can be used to realize urban land expansion and ecological protection.(3)The ecological security pattern of urban agglomerations is the key to the co-development of urban land expansion and ecological protection.Ecological source sites,corridors and key points constitute the ecological security pattern of urban agglomerations,which is the ecological background of urban land expansion in urban agglomerations.The combined effects of socioeconomic,natural,accessibility,and spillover effects on urban land expansion could be positive or negative,and socioeconomic and spillover effects are the main controlling factors affecting urban land expansion.Hence,the framework of the “four forces” mechanism for urban land expansion in urban agglomerations was put forward.(4)Under the framework of the symbiosis mechanism,different scenarios for urban land expansion were set according to the development needs of urbanagglomerations and ecological protection requirements,among which the coordinated symbiosis scenario turned out to be optimal.The coordinated symbiosis scenario aimed at economical and efficient land use.The ecological and economic benefits generated by various types of land have met the demand of people,and the goal of optimal allocation of land use in urban agglomerations was finally achieved.This scenario is conducive to ensuring the stable development of social economy in urban agglomerations and the maximization of ecological benefits,which is consistent with the goals and principles set out in the Changsha-Zhuzhou-Xiangtan Urban Agglomeration Regional Planning.(5)Based on the spatial attributes of the development and the ecological security pattern of the urban agglomeration,the functional attributes of control and guidance,and the morphological attributes of rigidity and elasticity,the growth boundary of the urban agglomeration was delineated.By innovating the growth boundary management mechanism of the urban agglomeration,meanwhile combining the ecological security pattern with space management and control,a multi-oriented growth boundary management and control system was established.Furthermore,a“flexiblility-succession-dynamics-feedback” growth boundary management and control model was built to lead to a governance system driven by control,expansion,and protection. |
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