| The construction of an ecological security pattern aims to reasonably and effectively protect and regulate the key ecological elements that exist or potentially exist to maintain and control specific ecological processes,thereby ensuring the sustainable supply of ecosystem services and functions,and promoting the harmonious coexistence of man and nature.As a special geographic unit of national land space,mountainous areas are characterised by ecological sensitivity,resource gradient and disaster-prone,while China is a mountainous country with complex human-land relations in mountainous areas.This dissertation uses the Qinling-Daba Mountains area,the main north-south transition zone in China,as the study area,and is based on the logical paradigm of "ecological source site identification-resistance surface construction-ecological corridor construction".The evolutionary mechanisms of ecosystem services and the trade-offs and synergies within the source areas were explored through geographical probes and correlation analysis.Spatial principal components were used to assign weights to the ecological source site spreading resistance factors and corrected for topographic relief to obtain the ecological source site spreading resistance surface.The minimum cumulative resistance(MCR)and gravity models are used to extract potential ecological corridors and to analyse their importance.Finally,the ecological safety pattern of the Qinling-Daba Mountains was evaluated by using comparative analysis and graph theory.The main conclusions are as follows:(1)During the period 2000-2020,habitat maintenance,climate regulation and soil conservation services in the Qinling-Daba Mountains show an inverted ’U’-shaped trend of growth followed by decline,while water conservation services show a declining trend over the 20-year period.The integrated ecosystem services in the Qinling-Daba Mountains are dominated by extremely important areas,with obvious spatial differentiation.The minimum area threshold for ecological source patches was set at 40 km~2,when the number of patches and the proportion of patch area began to stabilise.The overall potential connectivity of the potential ecological source patches and the number of patches in the landscape is set at 8 km,which is a good reflection of the subtle relationships between patches and is consistent with the actual ecological conditions.Combining the importance of integrated ecosystem services and the importance of landscape patches,the number of ecological source sites was identified as 17,20 and 26 in 2000,2010 and 2020 respectively,with the number of ecological source sites increasing while the total area showed a trend of first increasing and then decreasing.(2)During 2000-2020,the explanatory power of DEM,precipitation and GDP was greatest for habitat maintenance services;the explanatory power of DEM,temperature and GDP was greatest for climate regulation services;while precipitation and topographic relief had more significant effects on water conservation services;and topographic relief,precipitation and slope had the greatest effects on soil conservation services in the Qinling-Daba Mountains ecological source area.In terms of factor interaction detection,the four ecosystem services in the ecological sourceland are influenced by the interaction of multiple environmental factors,and the combined effect of two environmental factors on ecosystem services is greater than the independent effect of individual environmental factors.On a global scale,the three pairs of ecosystem services-habitat maintenance-water harvesting,habitat maintenance-soil conservation,and water harvesting-soil conservation-have always been synergistic during 2000-2020,and the three pairs of ecosystem services-habitat maintenance-climate regulation,climate regulation-water harvesting,and climate regulation-soil conservation-have gradually shifted from a trade-off to a synergy.At present,synergistic relationships between the four ecosystem services are predominant.From the bivariate local spatial autocorrelation results,the bivariate spatial autocorrelation of ecosystem services in the ecological source areas of the Qinling-Daba Mountains during 2000-2020 was dominated by high-high clustering synergistic relationships.Habitat maintenance-climate regulation high-aggregation synergies gradually shift from west to east,habitat maintenance-water connotation high-aggregation synergies are relatively dispersed,climate regulation-water connotation high-aggregation synergies expand from the southwest to the northwest,while climate-regulation-soil conservation and water connotation-soil conservation pairs of ecosystem services high-aggregation synergies gradually shift from east to west.(3)In general,the resistance surface of the ecological sourceland expansion in the Qinling-Daba Mountains is dominated by medium and low resistance areas;spatially,the layout is characterized by "high in the west and low in the east",with high resistance values in the areas west of the Jialing River,followed by a concentration of high values in the northeastern part of the Qinling-Daba Mountains in Henan Province.A total of 325 ecological corridors were identified,with a total length of 51,263.54 km,and 89 ecological nodes were extracted;in terms of spatial distribution,the ecological corridors show a network-like distribution pattern of "dense in the west and sparse in the east,dense in the north and sparse in the south".There are 6 primary corridors,16 secondary corridors and 303 general corridors,and the distribution of primary and secondary corridors is mainly in the central and eastern parts of the Qinling-Daba Mountains.(4)By comparing the spatial distribution and area overlap rates of nature reserves and ecological source sites in the Qinling-Daba Mountains,the regional characteristics of their concentrated distribution are basically the same,with 59 nature reserves overlapping with ecological source sites by as much as 73.28%.In addition,the network closure degree value of the ecological safety pattern in the Qinling-Daba Mountains is 0.63,the line point rate reaches 1.86,and the network connectivity degree γ is 0.74.The comprehensive comparative analysis and quantitative evaluation of the network structure show that the structure of the ecological safety pattern construction in the Qinling-Daba Mountains is reasonable,and the network connectivity and its structure are relatively complex. |
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