| China’s urbanization rate has been increasing since the reform and open,and the constructed land in cities has been expanding greatly.In the processes of urban expansion,ecological land is constantly occupied,and the integrity of the ecosystem is damaged,which seriously affects the sustainable development of the region.Urban expansion simulation can provide a useful guidance for orderly expansion of urban land and,further,taking ecological factor into urban expansion simulation it is of great significance for keeping the balance of development and protection.Although ecological factors had been taken into consideration in previous researches of urban expansion simulation,the influence of ecological connectivity was ignored.However,Ecological connectivity is of great significance to the development of regional landscape function and the maintenance of regional ecological security.Establishing an ecological network and connecting fragmented habitats is of great importance in this respect.In this paper,Zengcheng District of Guangzhou city is taken as the research area.Based on the evaluation of ecological land quality,ecological nodes are extracted,and ecological corridors are extracted by the method of minimum resistance path.By extracting ecological nodes and building ecological corridors among them,regional ecological network is constructed.Then,the protection of ecological network space is taken as the constraint condition,and the minimum cumulative resistance model(MCR)is used to simulate the urban expansion in different scales.Finally,the simulation results of urban sprawl are presented Compare with other cases.The main conclusions are as follows:(1)The main types of land use in Zengcheng district are forest land and cultivated land,which account for 78.5% of the total area of the study area.Taking forest land and grassland as ecological land,it is found that the ecological land in Zengcheng district has an obvious dominant position in the landscape composition,and its fragmentation degree and interference degree by human development and construction activities are relatively low.Construction land has experienced rapid growth in the past decade,and urban expansion is mainly marginal expansion.Combining patch area,Normalized Difference Vegetation Index(NDVI),landscape indexes of fractal dimension to evaluate the quality of ecological land,the results indicated that the high-quality ecological land is mainly distributed in the mountains in the north and the hills in the middle of Zengcheng district.The ecological land in the south is relatively fragmented and greatly disturbed by the construction and development activities.(2)Combined with the ecological land quality evaluation results and the Forest Park and Wetland Park planning data in Zengcheng District,40 ecological patches in Zengcheng district are selected as ecological nodes.Then,78 ecological corridors between ecological sources were constructed by the minimum cumulative path identification method,and 22 ecological nodes were set at the intersection of corridors.By extracting ecological sources and building ecological corridors,the ecological network was constructed.Based on the graph theory,the importance of ecological connectivity of sources and corridors were evaluated.The results indicated that the number of ecological nodes with high importance of connection was less,mainly including large Forest Park or natural forest patches in the middle and north of study area,and the number of corridors connected with high importance was also less,mainly short and medium distance corridors.(3)The ecological node,ecological corridor and stepping stone patch in the ecological network were taken as the ecological expansion "source" in the minimum cumulative resistance model,and the "source" is classified according to the importance of connectivity.In this way,the resistance surface of ecological expansion was generated by combining the location and natural factors.The resistance surface of ecological expansion was used to simulate urban sprawl.The results of urban sprawl simulation showed that the newly-added construction land is very concentrated in Xintang Town and Shitan town in the south of study area in the early stage.With the increasing intensity of urban expansion,the new construction land is concentrated in Zhongxin town and Licheng street in the middle of study area.The urban expansion space under the constraint of ecological network presents an obvious clustered distribution pattern.(4)Compared with the urban expansion scenario considering the ecological network constraints,the urban expansion space mainly layout in the edge of existing construction land in the scenario without the ecological network constraints.Urban expansion space in the scenario without the ecological network constraints showed spreading distribution characteristics,and had stronger interference on the formation of key ecological nodes and ecological corridors.The scenario which considered the restriction of ecological network protect the integrity of ecological network in a better level and benefit to the ecological function of the research area. |
