Exploration of ecological environment quality in the "Two Mountains, Seven Rivers and One Basin" area of Shanxi Province, China

The middle reaches of the Yellow River represent a critically ecologically sensitive and fragile area within the Yellow River Basin (YRB), holding significant scientific value for ecological security assessment and environmental management strategies. This study comprehensively evaluates the evolution of the eco-environment in the "Two Mountains, Seven Rivers, and One Basin" (TSO) area of Shanxi Province from 2000 to 2020 based on fraction vegetation cover (FVC) derived from the Normalized Difference Vegetation Index (NDVI), net primary productivity (NPP) calculated via the Carnegie–Ames–Stanford approach (CASA), and the remote sensing ecological index (RSEI). The results indicate a significant improvement in the TSO's eco-environment from 2000 to 2020, with the RSEI values increased from 0.34 in 2000 to 0.41 in 2020 (an increase of 17.76%). Both FVC and NPP demonstrated notable upward trends, with FVC increasing by 22.74% and NPP by 53.11%. Spatially, FVC rose by 21.84%, 19.72% and 26.06%, respectively in the Two Mountains, Seven Rivers, and the YRB in Shanxi Province. Similarly, the NPPs increased by 51.60%, 48.60%, and 61.65% in these regions over the past 21 years. Both FVC and NPP exhibited decreasing patterns from southeast to northwest, with significant eco-environmental improvements in the northern region and slower recovery in the southern region. Precipitation was the primary causes influencing vegetation recovery, showing positive trends in the central and northern TSO regions, while this trend reversed in the southern. The RSEI value indicate substantial eco-environment improvements in the central and northern areas (Sanggan, Daqing and Hutuo River Basins), whereas the southern regions (e.g., Zhang, Qin, Fen and Sushui River Basins) remain in poor grade. Human activities, particularly land use/cover changes marked by increased forestation and urbanization alongside decreased cultivated land, significantly affected vegetation cover patterns. This study provides scientific references for formulating policies on ecological construction and high-quality development in the YRB.