Do the ecosystems of Gansu Province in Western China's crucial ecological security barrier remain vulnerable? Evidence from remote sensing based on geospatial analysis

Under the dual stress of climate change and human activities, ecological problems such as vegetation degradation, soil erosion, and desertification have disturbed the balance of the human-land relationship, damaged the ecosystem integrity, and seriously affected the sustainable development of human societies and ecological environments. Scientifically assessing the stability or vulnerability of an ecosystem is a key prerequisite for measuring its degree of sustainability. Ecological vulnerability (EV) provides a reasonable quantitative pathway as the comprehensive result of ecosystem change. However, to meet the challenges of variable external interference, the capabilities of existing assessment frameworks require further improvement. This study constructed a novel comprehensive remote sensing index directly based on land surface characteristics—regional ecological vulnerability index (REVI) and assessed the spatio-temporal characteristics and driving mechanism of EV in Gansu Province during 2000–2020. The applicability of three objective methods, namely principal component analysis, entropy weighing method, and spatial distance model, was verified against field data, and the effectiveness of implementing major ecological programs was discussed. The results showed that: (1) EV intensity of the study area remained at a relatively high level, and its spatial distribution exhibited apparent latitude-longitude zonality and spatially stratified heterogeneity; (2) EV decreased in 41.926% of the study area but continued to increase in 1.235%, and it exhibited an overall conversion pattern of “significant decrease in large areas and increase in small areas” in the past 21 years; (3) the effectiveness of ecological programs determined their impacts on EV, regulating the contribution and interaction of water resources, vegetation cover, soil degradation, and human activities, and promoting sustainable development of the ecosystem in a vulnerable cycle; and (4) urban expansion was achieved at the cost of occupying cropland and ecological land, and became the primary cause for the increased EV. The framework presented in this study is suitable for large-scale EV assessment, even at the global scale, with higher application potential. The results have important reference value for ecological protection, land resource utilization and sustainable development of similar vulnerable ecosystems, which are helpful for formulating sustainable and coordinated development policies.