| Since reform and opening up,China has experienced a rapid urbanization process with remarkable achievements in social and economic development.However,in the meantime,this period also witnessed inefficient land use and damaging ecological environment.In the pursuit of economic development,Nanjing has experienced a similar situation as other big cities:urban built-area expanded exponentially,economic-development-oriented urban construction eroded agricultural land and ecological space continuously.Urban ecological security and eco-system integrity of Nanjing is suffering significant challenges.Facing the severe situation of environmental pollution,tight resource constraints and the degradation of ecosystems,our nation put forward the goal of "ecological civilization construction" and "New-type Urbanization".All cities gradually recognize the dangerousness of pursuing economic development without taking environmental protection seriously,come to emphasis on the balance of these two sides,and actively seek the strategic transformation of urban development.Urban Growth Boundary(UGB)is an effective tool to curb disordered urban spread and to guide the rational development of cities.UGB protects the natural resources through rigorous boundary and guides the quantity and development direction of urban construction through elastic boundary.Its implementary effects are consistent with current urban development goals,thus UGB attracts more and more attention in China.Although there are urgent needs for UGB,no mature technical process and unified delimitation method has formed.Previous methods emphasize either ecological protection or construction needs,seldom reflect the balance between the two sides.The delineation methods of rigorous boundary usually only passively protect existing ecological space,and often neglect the potential ecological space which has important ecological connection function to maintain the balance of urban and regional ecosystems.So that the designated ecological control units often become habitat islands in the city,and hardly exert the overall ecological effect.The elastic growth boundary needs to analyze the dynamic land demands of urban development,while existing methods either simply replace space management with land demand quantity or evaluate the threshold value instead of dynamic urban growth progress.Although there are some methods that could directly forecast urban growth in space,complex technical processes and difficult code operation frustrate most urban planners.In addition,previous methods still exist some deficiencies,such as strong subjectivity,poor spatial guidance,and ambiguous timing guidance and so on,which have become obstacles of UGB development and implementation.Taking Nanjing metropolis district as an example,this paper attempts to integrate static data analysis with dynamic land prediction by using the analysis methods of ecological sensitivity,ecological network and urban growth simulation under the guidance of ecological security pattern and smart growth theory.So that the rigorous growth boundary and elastic growth boundary of study area are scientifically developed.In the development of the rigorous growth boundary,existing high ecological sensitive spaces are identified through ecological sensitivity analysis,and potential ecological corridors and key ecological areas with important ecological significance to the study area are identified by least-cost path method.Landscape connectivity index based on graph theory are used to determine the width of ecological corridors,then the potential ecological networks of the study area are constructed.By integrating the existing and potential ecological spaces,rigorous growth boundaries are scientifically delimitated,protecting the existing and potential important ecological space.In the case of elastic growth boundary,four possible development scenarios are set up using SLEUTH model.By accuracy evaluation,the scenario that matches reality best is selected and used to predict elastic growth boundaries.The results show that:(1)The land for ecological protection and restoration identified by rigorous growth boundary is 1802.4 km2,accounting for 41.08%of the study area.Elastic growth boundary identify that the quantity of urban construction area would be confined in 1180 km2 and its plastic area is 1247 km2.Other conclusions are also obtained in the process of rigorous UGB development:1)Ecological sensitivity analysis is effective in identifying the existing high ecological sensitivity spaces,with the spatial pattern of high ecological sensitivity areas demonstrating that no matter how large or small,ecological sensitivity patches are usually isolated and scattered;and 2)By considering the ecological sensitivity areas simultaneously,71 sources,119 important corridors,and 61 key ecological patches were selected to develop the ecological networks.The developed ecological networks can significantly enhance the original landscape connectivity,and can effectively improve overall ecological security both at the urban and regional scales.The study indicated that ecological sensitivity analysis could capture the established natural status effectively but neglect the importance of potential ecological connectivity;however,ecological network analysis could make up for this shortcoming perfectly.Therefore,combining ecological sensitivity analysis with ecological networks analysis as performed in the present study is very useful and could be a good method to develop rigorous boundaries on different scales.(2)The conclusions of elastic UGB are as follows,1)In SLEUTH model,multi-scenario analysis can be not only applied to the prediction of future uncertainties,but also to the determination of historical growth pattern.Multi-scenario analysis helps to determine the process of urban growth that is most consistent with the real history,so that it can improve the accuracy of model predictions.2)SLEUTH model simulated urban growth in study area quite well,and the historical simulation accuracy of UGB is as high as 84.77%.The universality of SLEUTH model has been further validated.3)Core protection of urban ecology has difficulty in curbing urban sprawl.Bottom-line protection and eco-oriented urban development simply searches for suitable construction land,paying no attention to the agglomeration effects of socio-economic factors,so there is a possibility of invisible urban sprawl.4)Elastic growth boundaries developed by "multi-factor fusion scenario" take into account social,economic,location,traffic and other driving factors and ecological environmental protection constraints,reflecting ecological priority and smart growth ideas.This thesis establishes a set of concise analysis framework and easy-to-operate technology for the scientific delimitation of UGB,which can provide an important reference and method support for the delineation of UGB in the study area and other cities.The results of the study can provide important references for the delimitation of ecological control line in Nanjing,and provide important decision-making basis for Nanjing urban planning,land use planning,ecological corridor and green infrastructure construction planning.At the same time,the research conclusions also have referential value for the docking of ecological corridors at the regional level,the regional co-ordination of ecological resources and so on. |
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