| In recent years,high-intensity land development has continuously eroded the ecological patches and deepened the degree of landscape fragmentation in the city with the acceleration of urbanization and the rapid development of economy,thus reducing the connectivity of ecological patches in the region,isolating different biological populations,incomplete ecosystem service functions,and seriously threatening biodiversity.Using corridors to connect ecological patches and optimize ecological networks can protect and improve their connectivity,which plays an important role in maintaining urban ecological benefits.Taking Xiangyang City in Hubei Province as an example,based on the data of five time phases from1997 to 2017 on various geographic information system(GIS)platforms,the landscape indices,morphological spatial analysis method(MSPA),graph theory index and the minimal cumulative resistance(MCR)model were used to analyze the current situation and changes of landscape pattern,identify ecological patches and potential ecological networks in the study area,and analyze the changes of ecological networks in different periods.The analysis results were as follows:(1)The number of patches(NP),patch density(PD)and Shannon's diversity index(SHDI)increased significantly,contagion index(CONTAG)and articulation index(AI)decreased gradually on the landscape scale of Xiangyang City,suggesting that the patch fragmentation deepened and complexity became higher.However,the patch cohesion index(COHESION)still remained at a relatively high level,which indicated that the flow level between different patches was relatively high,and the connectivity had not decreased significantly due to landscape fragmentation.In addition,the change of type scale was mainly related to the large-scale expansion of construction land,and the original forest patches were seriously eroded under the pressure of agricultural and construction land.The main changes in villages and towns were that the increase of the number and density of patches contacted with the surrounding areas of the built-up areas,agricultural land and forest land were significantly higher than those in other areas.In recent years,the changes of the core ecological patches and central urban area tended to be stable with the promulgation of the national policy about protecting the natural environment and the improvement of the central urban area construction.(2)The patch area in the core area of Xiangyang City was continuously decreasing,among which the larger forest patch was seriously eroded,while other types of patches mostly showed a trend of increasing first and then decreasing,which was closely related to the slowdown of the trend of erosion and fragmentation of the core area due to the protection of the ecological environment by the state in recent years.Using graph theory index analyzed the patch connectivity in the study area based on the analysis results of morphological spatial pattern analysis,the results showed that integral index of connectivity(IIC),probability of connectivity(PC)and consistency chance of patch(CCP)all showed an upward trend of volatility,indicating that the connectivity remained at a high level in the study area.However,the Flux and Harary indexes decreased,suggesting that the connection resistance between different patches increased.Moreover,the betweenness centrality(BC)and density-group index(Dg)were both maintained at a relatively high level in the western mountainous area,but showed different degrees of decline in the southeast hilly area due to the interference of human activities.(3)The MCR model was used to generate the potential ecological network of patches complete connection and 10 km connection threshold in each year in the study area.The results showed that the average resistance of corridor increased from 1.57 to 1.60 when the patches were completely connected,and when the connection threshold was 10 km,the average resistance of the corridor increased from 1.56 to 1.61.The number of high resistance corridors(average resistance > 2)and the average resistance of all corridors in the potential ecological network were the highest in 2017 compared with other years.However,the potential corridors in the study area gradually concentrated to the southern region under the ideal condition of no distance threshold limit due to the increasingly serious interference of human activities in the source patches in the central and northern regions.Moreover,the number of corridors decreased significantly in the southeast hilly region,and the potential ecological network showed serious degradation from 1997 to 2017,affecting the maintenance of the stability of the ecosystem in the region.(4)The network closure index(?),network connectivity index(?)and network connectivity rate index(?)were used to evaluate the potential ecological network with 10 km connection threshold.The results showed that ? and ? index decreased from 0.772 and 0.849 in 1997 to 0.723 and 0.815 in 2017,respectively.This indicated that the number of loops in the potential ecological network and network connectivity gradually decreased in the study area,i.e.the number of routes that could be selected during the migration and communication of biological species gradually decreased and the degree of difficulty increased. |
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