| The rapid urbanization process not only improves the living standard of urban residents,but also changes the original urban landscape with the rapid expansion of urban land use scale,which greatly restricts the green and sustainable development of cities.It is of great significance to analyze urban landscape pattern and ecological environment characteristics,improve regional ecological environment and construct urban landscape security pattern.Ya ’an is known as "the lung of Tianfu" and "the gene bank of animals and plants",which is the fundamental principle for conducting research on land use change and landscape ecological pattern construction under the new situation.Ya ’an is the ecological ladder of the transition from the Sichuan Basin to the Qinghai-Tibet Plateau,the hometown of giant pandas and the birthplace of world tea culture.This study takes Ya ’an as the research object,involves the transformation of urban land use types,and uses remote sensing technology,GIS technology,landscape pattern analysis and other methods to comprehensively analyze and evaluate the landscape pattern of Ya ’an and its impact on the urban ecological environment.To construct the landscape ecological security pattern in Ya ’an,Sichuan Province,one of the most important biodiversity hotspots in China.This study provides a scientific basis and a reference example for the construction of rational urban landscape planning and the harmonious development of urban and ecological environment.Firstly,based on the land use data of the study area from 2000 to 2020,this paper analyzed the structural changes of cultivated land,woodland,shrub,grassland,water area,construction land,bare land and glacier in Ya ’an during the past 20 years through the land use transfer matrix.Landscape fragmentation(Ci),patch number(NP),patch density(PD),proximity index(PROX＿MN),patch area(CA),degree of separation index(DIVISION)and degree of convergence index(AI)were selected to calculate the landscape pattern in 2000,2005,2010,2015 and 2020 The MSPA model and MCR model were used to construct the landscape ecological security pattern of Ya ’an.The MSPA model was used to identify eight landscape types including branch,edge,perforation,ring,island,core opening,core area,edge opening and connecting bridge in the study area,and the core area patches were extracted.Land use type,slope,elevation,vegetation cover and road were selected as first-level indicators to construct the comprehensive index system of MCR model.The arcgis10.5 cost path tool was used to identify potential ecological corridors in the study area.The Linkage Mapper tool was used to build potential ecological corridors,and 20 ecological corridors were identified by eliminating redundant ones.The main research results are as follows:(1)The land use types of Ya ’an are mainly woodland and cultivated land,followed by grassland.The sum of the area of the three land types exceeds 95% of the total area of the study area.Among all land use types,grassland and woodland have the largest area base and the most drastic change.Forestland-arable land,forestland-grassland,cropland-woodland,grassland-woodland are the main types of land transformation in Ya ’an.The overall change range of the area of various land use types is small,and the change of woodland area is more significant,which decreased by 2.28% in 2020 compared with that in 2000.The change degree of other land types is not significant,and the structure of the quantitative relationship among different areas basically remains unchanged.According to the characteristics of topography and topography,there are significant differences in the distribution,which shows the distribution characteristics of arable land in the north,middle and west,and near the water area,and woodland in the north and southwest.Other land use types mainly show a mixed and scattered distribution trend.These changes may be due to the implementation of the policy of returning farmland to forest in recent years,ecological environment construction and management projects,panda base and tourist area planning and construction of human activities.(2)Landscape pattern indices of different land types in the study area: from 2000 to 2020,four types of proximity indices of grassland,arable land,woodland and shrub changed significantly,and their spatial distribution changed significantly.The proximity index of other land classes did not change significantly.The patch density index and aggregation index of cultivated land in the study area changed significantly in 2010,while the patch density index and aggregation index of other land classes did not change significantly,and the overall level of the separation index remained unchanged.The density of grassland patches was higher than that of other land classes in all years,and the degree of grassland fragmentation was higher in Ya’an.(3)10 patches with core area greater than 100km2 were selected as the ecological source area of the study area,and 10 patches with DPC index greater than 1 were added as the ecological source area.The northern part of the study area was qualified as the high-quality habitat patch under the study standard.There are 20 ecological source patches in Ya ’an,with a total area of 10307.06km2,accounting for 68.49% of the total area.By superimposing each single factor resistance surface,the total resistance value of the study area is calculated to be between 1 and 4.76,and the resistance value of the study area is generally low.Based on the above results of ecological source and resistance surface,this study adopted two different methods to construct ecological corridors.A total of 21 ecological nodes were identified.The generated low-resistance corridors were superimposed with river corridors,national roads,provincial roads and built-up areas,and the intersection points were found.The intersection points of river corridors and land corridors and land corridors were regarded as general ecological nodes.(4)The focus of this study was to identify Ya ’an ecology,ecological corridor,the important ecological corridor,in general,the important ecological ecological node,ecological corridor,on the basis of this connection with national ecological function zoning,each landscape component partition,zoning,corridor group improve and optimize the construction of landscape ecological security in the study area.The superposition analysis of the results and the distribution of nature reserves showed that these corridors could effectively improve and stabilize the landscape ecological security pattern,and further promote the development of biodiversity in Ya ’an.The study further put forward the countermeasures to optimize the landscape ecological security pattern. |
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