| The ecological security of the Three Gorges Reservoir Area is of great significance to the whole Chongqing and even the upper reaches of the Yangtze River.In recent years,affected by natural factors and human activities,the regional landscape pattern has been constantly changing,which further affects the land use and landscape ecological security.The analysis of spatiotemporal heterogeneity of landscape ecological security will be beneficial to establish the early warning mechanism of ecological risk,reducing the probability of ecological risk,to maintain regional ecological security.In this paper,Zhong County,the hinterland of the Three Gorges Reservoir Area was taken as the research object,with the use of 3S technology,taking four periods of remote sensing image data in 2000,2006,2012 and 2018 as the main data sources,as well as with terrain,climate and human activities combined,to make an in-depth analysis of the land use and landscape pattern in the study area from the perspective of time series and spatial scale.On this basis,based on the function,organization and stability of the study area,the evaluation of the degree of landscape ecological security was carried out,and the influencing factors of landscape ecological security was explored.According to the influencing factors,methods of ecological restoration were sought out,in order to provide theoretical basis and scientific suggestions for the ecological protection and sustainable development of the study area.The main conclusions of this study are as follows:(1)At present,the main type of land use/cover in Zhong County is cultivated land,which accounts for more than 59%of the total area in the four periods.The cultivated land is a continuous distribution pattern in the form of large area interactive coverage,dominant in the landscape.Other types of land use/cover are embedded in the cultivated land landscape patches in the form of block pattern,line pattern,point pattern,or dispersion and aggregation.During the 18 years,all types of land use/cover showed a trend of"three increase and three decrease",which was mainly manifested as:forest land,construction land and water area increased by 93.91 km~2,83.33km~2 and 35.07 km~2 respectively,while grassland,cultivated land and unused land area decreased by 104.48km~2,99.15 km~2 and 8.69 km~2 respectively.With the passage of time,the growth rate of construction land area accelerated.The change of cultivated land and woodland was relatively stable.Unused land was constantly being developed,the area of which was greatly reduced.(2)The degree of land use in the study area had been improved,and the land use was developing towards diversification and homogenization.The areas with relatively high land use comprehensive degree was mainly located in the middle reaches of the Yangtze River,where was the main urban area of Zhong County and near the northwest area.From 2000 to2018,the change map of land use/cover type was mainly from cultivated land to woodland,grassland and unused land,and forest and grass land to construction land.Stable chromatographic units accounted for the largest proportion among all kinds of variation pattern chromatographic units,39.90%of the total area of the study area,and regional topography,population growth,economic level and policies and regulations were the main factors affecting the change of regional land use/cover types.(3)The degree of landscape fragmentation in Zhong County was alleviated,with the aggregation degree of patches increasing,the connectivity degree between patches increasing,as well as the landscape pattern tending to be more complex.The heterogeneity of landscape increased,of which the degree of human disturbance increased.In recent years,construction land has been most significantly affected by human activities,the grassland scattering around woodland with the highest degree of fragmentation.The distribution of grassland and unused land was smaller and more uneven.The number of patches increased,with the fluctuation of area-weighted average shape index increasing,the dimension of area-weighted average decreasing,and the patch shape tended to be complicated.(4)From 2000 to 2018,the landscape ecological level of Zhong County declined,and the critical safety area was mainly transferred to the low ecological security area,while the range of the high ecological security area was gradually reduced.The area of the four periods was 13.40%,61.32%,28.34%and 13.33%,respectively.The low ecological security areas were mainly concentrated in the northeast and central part of the study area,while the high ecological security areas were mainly concentrated in the Yangtze River and its two sides and the areas with good vegetation coverage in the northwest.The Moran'I values of landscape ecological security in the four periods were all greater than 0.5,showing a strong positive spatial correlation,and the trend of agglomeration increased first and then decreased.The autocorrelation pattern of landscape ecological security degree in the four periods was consistent,and the high value-high value and low value-low value regions were dominant.The high value-high value region was concentrated in the Yangtze River Basin,and the low value-low value region was mainly distributed in the central and northern part of the Yangtze River Basin.(5)The main obstacle to landscape ecological security had changed from functionality to stability.The complexity of landscape pattern,such as patch connectivity,aggregation and fragmentation,hindered the improvement of landscape ecological security quality.The linear correlation coefficient between vegetation coverage and landscape ecological security degree in the study area was 0.731,indicating that vegetation coverage in the study area determined about 3/4 of the landscape ecological security degree area.For different altitude,slope direction,slope degree of landscape ecological security of the three-dimensional model of trend surface analysis,landscape ecological safety area of low concentration in the hilly area,slope direction(22.5°-67.5°)in northeast China,east direction(67.5°-112.5°)and the altitude of 100 m,400 m cross area,with the increase of altitude,landscape ecological security index showed increasing trend.In low altitude area,slope played little influence on landscape ecological security degree.With the increase of altitude,the smaller the slope,the degree of landscape ecological security was greater.And the greater the slope was,the smaller the degree of landscape ecological security was.According to the spatiotemporal dynamics of landscape ecological security in Zhong County,four ecological function zones were put forward,which were the ecological key restoration area,the ecological vegetation construction area,the ecological agriculture development area and the ecological security maintenance area.The main ecological construction emphases of each district were discussed,which provided a valuable reference for understanding and planning the regional development,in order to improve the landscape ecological security level of Zhong County gradually. |
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