| China is the second largest economy in the world.Since the reform and opening up,it has experienced a rapid urbanization process.Urban land,as the carrier of social and economic development,has obvious expansion characteristics in recent years.While bringing huge economic benefits,its disorderly spread also threatens the regional ecological environment and food security.The lack of reasonable planning and management of urban space will lead to the blind expansion of urban land to the surrounding areas,which will lead to a series of urban problems,such as the decline of ecosystem services,the decline of cultivated land quality,the waste of land resources and so on.Therefore,it is necessary to put the task of protecting the ecological environment and ensuring food production into the blueprint of future urban land layout planning,and design a spatial optimization scheme to maximize the comprehensive benefits of society,economy,food and ecology,so as to alleviate the contradiction between urban development,ecological protection and food production.Based on the scientific basis of land and space planning,this study takes Changzhou City as the research area,grasps the spatio-temporal evolution law of urban expansion in the study area based on multi-source spatio-temporal data,analyzes the response of ecological environment and food security in the process of urban expansion over the years,quantifies the quality of ecological space and food production potential,and integrates it into the urban expansion model,it shows the spatial layout of future urban development in a multi scene way.Finally,the paper describes a spatial pattern optimization scheme to coordinate ecological protection,food security and urban construction,which can provide reference for relevant departments to formulate future urban development policies,and help to realize urban green and sustainable development.The main research contents and conclusions of this paper are as follows:(1)Urban land expansion process and impact analysis.Through a variety of spatial analysis methods,the spatial and temporal evolution characteristics of urban land expansion and its impact on ecological environment and food production in the study area from 2009 to 2018 were studied.The results show that the scale,intensity,landscape pattern and center of gravity of urban expansion in the study area have certain regularity,and urban expansion poses a great threat to ecological protection and food security.In recent years,the intensity of urban expansion in the study area gradually decreases with time,the number of fragmented urban patches gradually increases,the shape tends to be complex and irregular,and the degree of fragmentation increases year by year.The center of gravity of urban land moved to the southwest in general,and after the adjustment of administrative divisions in 2015,the center of gravity moved sharply.During the study period,the urban expansion caused the loss of 812200 tons of carbon storage,and occupied 3822.94km2 of arable land.The sown area and the total grain yield gradually decreased,facing greater ecological protection and food security problems.(2)Evaluation of ecological space quality and estimation of grain production potential.In this paper,invest model is used to evaluate the quality of ecological space,and cultivated land grading method is used to estimate the grain production potential in the study area.The results of ecological space quality evaluation showed that the areas with high ecological space quality in the study area were small,mainly concentrated in Taihu Lake,Gehu Lake,Yangtze River and the surrounding wetlands,Xiaohuangshan ecological public welfare forest,Xinlong ecological forest and Yancheng forest park.The land area with low ecological space quality accounts for a large proportion.In recent years,due to the rapid urban expansion,the ecological quality of the surrounding areas of the town is poor,so it is urgent to protect the ecological land;The results showed that the grain production potential of each patch ranged from 432.47 kg / a to518.75 kg / a,and there was a spatial difference in grain production potential.The highest difference in per unit area yield of different patches was 86.28 kg / a,it is mainly distributed in the west of Wujin district and the west of Xinbei district.(3)Simulation and optimization of urban land expansion.The first mock exam results show that Blending strategy integrates three machine learning models,and has higher accuracy than single model.It can predict urban expansion effectively by combining cellular automaton model.In the cellular automata model,the results of ecological spatial quality and grain production potential with different weights are set as spatial constraints to show the urban development pattern of the study area in 2030 under the four scenarios of current situation continuation,strict cultivated land protection,strict ecological protection and overall development.Compared with the results of different scenarios,the high-quality ecological land and high-quality cultivated land in the overall development scenario are protected to a higher degree,which can effectively solve the ecological protection and food production security problems caused by the future urban expansion in the study area.Based on this scenario,optimize the layout of future urban development,design the sustainable development plan of ecological protection,food security and urban construction.This paper proposes a new method to obtain CA model cell transformation rules by using blending strategy to fuse multi machine learning models,which enriches the urban expansion model.At the same time,it quantifies the quality of ecological space and grain production potential,integrates it into the urban expansion model,shows the spatial layout of future development,and depicts a blueprint of urban spatial optimization to maximize the comprehensive benefits of society,economy,grain and ecology,so as to provide decision support for relevant departments. |
