| Since reform and opening up,China has experienced a rapid urbanization process with remarkable achievements in social and economic development,in the meantime,the proportion of urban population has rose from 10.64%to 57.35%.The rapid growth of population and insufficient land area promoted urban land space expansion,which resulting in changing the nature of the underlying surface of the city and increasingly fragmenting the habitat patches.These phenomena seriously damaged ecological environment and weakened the urban ecosystem services and sustainable development ability of the city.The green infrastructure(GI)is a multifunctional green space network,which contains a variety of natural and artificial landscape and ecological elements.Green Infrastructure is the cornerstone of urban livability and sustainable development.The multifunctional characteristic of green infrastructure can improve many services of the city,and the connectivity of urban green infrastructure can significantly improve the biodiversity and sustainable development ability of cities,which is of great significance to maintaining the health and stability of urban ecosystems.However,the traditional methods of GI construction have some limitations in analyzing the importance of patches or corridores,determining corridor width of different geo-spatial position and planning of multiple pathways.The circuit theory is a new method of GI construction,which can make up for the deficiency of traditional GI construction because it integrates the random walk theory into the measurement of landscape connectivity.However,there are few cases to construct the urban GI pattern using the circuit theory,and rarely considered the effect of map boundary when using circuit theory.In the present study,we used circuit theory to map the landscape connectivity of GI in the main urban area of Nanjing.In the first step of our approach,we analyzed the effect of map boundary.Artificial boundaries on a map occur when the map extent does not cover the entire area of study;edges on the map do not exist on the ground.These artificial boundaries might bias the results of animal dispersal models by creatingartificial barriers to movement for model organisms where there are no barriers for real organisms.Here,we palced a buffer around the study area as a solution to this problem.The optimal buffer width is determined by calculating the current density correlation and the Manhattan distance under different buffer widths.Then,we used the circuit theory to quantitatively analyze the landscape connectivity between natural ecological patches in the main urban area of Nanjing,and identified all the potential pathways between natural ecological patches and analyzed the relative importance of patches and corridors according to current density.Next,we used a search window to detect barriers of the study area with the help of GIS software linkage Mapper tool,and then used the circuit theory to quantitatively analyze the influence of barriers on landscape connectivity.Finally,based on the above analysis,we constructed GI network in Nanjing and put forward a specific strategy of GI network pattern optimization landscape connectivity optimization strategy for Nanjing.The main conclusions of this study are as follows:1)Artificial map boundaries overestimate resistance values,and the map boundary caused more biases around the edge than the whole or core area of the research region.The method of placing buffer outside the research area can effectively remove the deviation of circuit theory simulation,and even a very narrow buffer(4%of the study area width)can effectively eliminate the effect of map boundary.A 3000m buffer(13.3%of the width of the study area)can basically remove the effect and when the buffer width was greater than 7000m(the width of the study area is 30%),the effect of map boundary can be completely eliminated.And the best buffer width of Nanjing is 3000m.2)Habitat fragmentation in the main urban area of Nanjing was significant.The total area of the patches was about 70.45 km2,and 40%of patches area had a low contribution to connectivity.The southern part of the study area exhibited the best landscape connectivity,followed by the middle and northern parts.In the south,numerous corridors clustered into net structure,and the network structure is complex.In the middle of the study area,the Qinhuai River mainly formed a circular corridor.Relatively few corridors were observed in the northern part of the study area,and the patches were isolated.There were 155 barriers in the study area,and 84.5%of those barriers were>5 ha,so the landscape connectivity in the main urban area of Nanjing can still improve greatly.Based on the above results,we combined the important patches,important corridors and the important area after removing barriers points into Nanjing GI network.Then,we adjusted the GI network according to satellite map and divided the GI network into ecological key area,ecological maintenance area,ecological restoration area and ecological improvement area.Finally,we put forward some specific GI optimization strategies,such as protecting important GI elements,restoring necessary landscape corridor and reducing barriers'resistance.Although many methods have been developed and used for predicting connectivity,circuit theory has rarely been used to map connectivity in urban areas.The present study demonstrates how circuit theory can be used to map connectivity in complex landscape and to identify important habitat patches and movement corridors for conservation planning,which is an advance in mapping the landscape connectivity of GI.The circuit theory incorporates all possible pathways and combines structural and functional corridors,which improves corridor redundancy and provides an efficient and cost-effective tool for mapping GI landscape connectivity.The results of this study provided an important reference for Nanjing GI networks.The whole thesis contains about33 579 words,31 pictures and charts. |
PDF Full Text Request