| As the most sensitive and fragile region in the global ecological environment,the alpine pastoral region is an important ecological security barrier in China and even in Asia.In recent years,with global changes and rapid social-economic development,various eco-environmental problems have emerged frequently,such as climate warming and humidification,glaciers melting,wetland shrinkage,grassland degradation,and land desertification,which have severely restricted the sustainable development of local human society.Ecological security is an important guarantee for human survival and plays a vital role in sustainable development.However,the exploration and understanding of ecological security assessment and its mechanism in alpine pastoral regions are not comprehensive.In addition,few studies have carried out validation and uncertainty analysis of ecological security assessment models,which often weakens the reliability of assessment results.This study takes the Gannan alpine pastoral region(GAPR)on the northeastern Tibetan Plateau as the study area,constructs an ecological security evaluation framework based on ecosystem health,ecological risk,and ecosystem services,and introduces remote sensing ecological index(RSEI)and high-resolution image to verify the reliability of assessment results.Finally,the spatiotemporal variation characteristics and influencing factors of ecological security in GAPR is analyzed and discussed.These results can provide a scientific basis for the socioeconomic development and ecological protection of the study area.The main results are as follows:(1)The analysis of the importance of variables by random forest algorithm shows that elevation and slope are the variables that have the greatest impact on land use classification.The overall accuracy and Kappa coefficient values range from 86.94%–93.86% and 83.14%–92.16%,respectively.The largest land use type in GAPR is grassland(58%–60%),followed by forest land(5%–28%)and cultivated land(6–10%),with the smallest proportion of construction land(<0.71%).Spatially,grassland is mainly distributed in the northwest of the study area,while forest land is concentrated in the southeast.(2)During the study period,the overall ecosystem health index in GAPR shows a fluctuating upward trend.The spatial distribution of overall ecosystem health level shows a decreasing trend from southwest to northeast,and the most areas are above the ordinary health level,accounting for the total area of more than 68.33%.Relatively well and well ecological health levels are mainly distributed in Maqu County,Diebu County,and Luqu County,while weak and relatively weak ecological health levels are distributed in Lintan County and Xiahe County.In the past 20 years,the area of ordinary health level has gradually decreased,that of relatively well and well ecological health levels have first improved and then deteriorated,while that of the weak ecological health level shows an increasing trend.(3)Constructing ecological risk assessment results based on landscape ecological risk and ecological sensitivity is more realistic.The results show that the landscape ecological risk in GAPR presents an upward trend,and the ecological risk levels are mainly lower risk and lowest risk.The ecological sensitivity is dominated by lightly sensitive and moderately sensitive levels,and the area of the non-sensitive zones has decreased while the area of the moderately sensitive area has increased.Overall,the ecological risk shows a fluctuating and increasing trend of first decreasing and then increasing.The risk level is mainly medium risk and below,which is mainly distributed in the pastoral areas of the northwest of the study area,while the areas with higher and highest risk account for a small proportion.(4)From 2000 to 2020,food production service has increased significantly,carbon sequestration,water yield,and soil conservation show a fluctuating increase trend,and the changes in habitat quality are relatively stable.There are significant differences exist in the spatial distribution of the five ecosystem services.High food production areas are distributed in Lintan County.The carbon sequestration,habitat quality,and soil conservation services show a spatial distribution pattern of high in the southeast and low in the northwest,while the water yield service shows a spatial distribution of high in the south and low in the north.The ecosystem service index shows a fluctuating and increasing trend,and the spatial distribution pattern is high in the southeast and low in the northwest.The ecosystem service level is dominated by medium services,and the higher and highest service levels are distributed in the southeast of the GAPR.(5)The comprehensive ecological security index(CESI)of GAPR has shown a fluctuating upward trend over 20 years,indicating that the overall ecological security situation has improved.The assessment results verify that the correlation coefficient(r)between the CESI and the RSEI is between 0.653 and 0.745,and the spatial distribution is basically consistent with RSEI and high-resolution images.The ecological security level of the study area is mainly moderate and above,accounting for more than 81.48%of the total area.Spatial,the lower and lowest ecological security levels areas are concentrated in Xiahe County,Lintan County,and Bailongjiang River Basin,while higher and highest security areas are distributed in Maqu County,Diebu County,and Zhouqu County.The change detection shows that the ecological security level in the study area is dominated by the unchanged region from 2000 to 2020,of which the fluctuation and unchanged area accounted for 36.90%,and the perennial unchanged area accounted for 22.19%.(6)The results of spatial correlation analysis and bivariate spatial autocorrelation analysis both show that ecological security has a strong positive correlation with ecosystem health and ecosystem services,while showing a negative correlation with ecological risk.Univariate spatial autocorrelation shows that ecological security exhibits a high degree of spatial clustering characteristics,dominated by “high-high”and “low-low” clusters,showing spatial polarization.In addition,the center of gravity of lower and lowest ecological levels shows a northward shift trend,while the middle ecological level and above show a southward movement characteristic.Socioeconomic factors have a greater impact on ecological security than natural factors and landscape indices,and the interaction between any two influencing factors enhances changes in ecological security.Among them,average annual precipitation,industrial added value,per capita GDP,chemical fertilizer consumption,urbanization rate,and grazing pressure are identified as the dominant factors affecting ecological changes in GAPR. |
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