Study On Delimitation Of Urban Growth Boundary Based On Ecological Security Pattern

In the past 40 years of reform and opening up,China’s urbanization process has been advancing rapidly.However,the expansion of urban land excessively depends on the disordered and extensive consumption mode of land resources,resulting in the erosion of a large number of high-quality cultivated land and ecological land.Facing the current severe situation of serious environmental pollution,ecosystem degradation and tight resource constraints,as well as the growing demand of the people for the ecological environment,China is also constantly strengthening the ecological environment protection and accelerating the top-level design and system reform of ecological civilization.In the aspect of urban and rural construction planning,urban growth boundary,as a technical means and policy tool to curb urban sprawl and guide the orderly development of urban space,has been widely studied and applied in practice.At present,the research on the delimitation of urban growth boundary is still in the stage of exploration and expansion,and has not yet formed mature and systematic operational rules of delimitation methods.China has also implemented a series of spatial management and control tools with Chinese characteristics similar to the urban growth boundary to control the unlimited expansion of cities and coordinate the contradiction between urban ecological protection and spatial growth demand.However,in the process of practice,the spatial planning is self-contained and lack of interaction mechanism,resulting in the conflict between scale boundaries,the contradiction of land use rights,and the difficulty in coordinating the interests of various departments,which seriously restricts the development and protection of land and space.Therefore,how to ensure the social and economic development,at the same time,through the rational delimitation of urban growth boundary,alleviate the contradiction between urban development and habitat protection,Realize the organic unity of smart growth of urban development and precise protection of ecological environment,is still an important topic of current research.As a typical representative of mountain city,Chongqing’s unique landscape pattern has gradually formed a"multi center,group"urban spatial structure.Compared with plain city or single center city,the complex topography and geomorphology lead to more limited space for construction land expansion,and the mountain sensitive environment constraints make the ecological environment protection more challenging.In view of this,this paper takes the main urban area of Chongqing as the research object and fully grasps the evolution law of land use landscape pattern and ecosystem service value in the research area from 1995-2019.On the one hand,it comprehensively analyzes the regional ecological environment quality,constructs the ecological security pattern and delimits the rigid growth boundary of the city;on the other hand,it uses the linear programming model and the flus prediction model to improve The objective function and constraint conditions are set for the purpose of regional ecological benefits.The scenario of land use optimization in the main urban area of Chongqing in 2035 is predicted by simulation,and the boundary of urban elastic growth is defined.At the same time,the paper puts forward countermeasures and suggestions from three aspects of technology optimization,policy system and long-term management mechanism.The main conclusions are as follows:(1)From 1995-2019,the landscape pattern in the main urban area of Chongqing changed significantly.In terms of quantity structure,each land use type shows the change characteristics of"one rise,one fall and four stability".That is to say,the area of construction land is on the rise,the area of cultivated land is on the decline,and the area of forest land,grassland,water area and unused land is basically stable.The transfer in type is mainly construction land and forest land,and the transfer out type is mainly cultivated land and forest land.In terms of spatial form,the overall landscape structure is developing towards the direction of complexity,the degree of patch separation is gradually expanding,and the connectivity and the proportion of the number of dominant types of patches are decreasing.The value of ecosystem services(ESV)in the study area is decreasing,and the contribution rate of cultivated land and forest land to the value of regional ecosystem services is the largest.(2)The quality of ecological environment in the main urban area of Chongqing is from low to high,showing an increasing trend of radiating and extending from inside to outside based on Yuzhong District.The high-quality regional landscape types are mainly cultivated land and forest land,while the low-quality regional landscape types are concentrated in construction land.According to the ecological environment quality and strategic layout of the study area,the ecological security pattern is constructed and divided into three levels:high,medium and low.The identified birthplace is1668.52km~2,accounting for 30.34%of the total area of the study area.There are 21ecological corridors with a total length of 515.5km and 40 ecological nodes.The ecological origin is regarded as the rigid growth boundary of the city.In this paper,a small amount of urban rigid growth boundary is used to ensure the regional ecologic security,avoiding the disorderly expansion of cities occupying high-quality ecological land.(3)The construction land is extracted from the land use scenario in 2035 in the main urban area of Chongqing for revision.Finally,the scale of urban elastic growth boundary is defined as 1825.72 km~2,the scale of existing construction land within the boundary is 988.66 km~2,and the reserved space for urban development by 2035 is837.06 km~2.The planning service life of the reserved space is reclassified according to the three stages of short-term,medium-term and long-term,so that the expansion as a whole meets the distribution law from the inside to the outside.The elastic growth boundary defined in this paper accords with the general law of urban expansion,meets the regional demand for land supply in the next 15 years,and can effectively guide the coordinated and high-quality development of cities.