Spatio-temporal variations of vegetation cover in the Qilian Mountains from 2000 to 2023

The Qilian Mountains (QLM) are characterized by their ecological fragility and environmental sensitivity. Vegetation, the dominant ecosystem in this region, plays a crucial role in water conservation, climate regulation and biodiversity protection. Based on fractional vegetation cover ( FVC ) data, this study employed trend analysis, Pearson correlation analysis, and PLS-PM (Partial Least Squares Path Modeling, PLS-PM) methods to investigate the current distribution characteristics of vegetation in the QLM in 2023 from the perspectives of annual and intra-annual variations, with a detailed exploration of its latitudinal zonality and regional differentiation patterns. Additionally, the spatiotemporal trends of vegetation changes in the QLM from 2000 to 2023 were analyzed, and the contributions of various influencing factors to vegetation dynamics were assessed both qualitatively and quantitatively. The results indicated that: (1) In 2023, the FVC in the QLM exhibited a pattern of lower values in the northwest and higher values in the southeast, with overall vegetation coverage being relatively low. The Huangshui River Basin (HB) had the highest mean FVC at 0.51, while the Haerteng River Basin (HETRB) had the lowest mean FVC at 0.05. Mean FVC decreased with elevation, peaking in the 2,500–3,000 m altitude range. The 98°E longitude line served as a distinct boundary, with more abundant vegetation coverage in the east than in the west. Higher monthly mean FVC values was observed between June and October. Vertical zonal differences in FVC distribution across different basins were significant, with the maximum FVC value of 0.96 observed in July within the 3,000–3,500 m elevation range of the HB. (2) From 2000 to 2023, vegetation in the QLM showed an increasing trend, with the rate of increase fluctuating with elevation and exhibiting upward fluctuations with increasing longitude. Significant differences in vegetation change rates were observed across different basins. The Shiyang River Basin (SYRB) had the highest average annual FVC increase rate at 0.40 %, while the HETRB and the Yuka-Tataleng River Basin (YKTTLRB) had the lowest rates at 0.13 %. The average FVC change rate demonstrated a significant increasing trend from May to October. (3) Climate remained the primary driver of vegetation growth, exerting a significant direct effect on FVC with a coefficient of 0.9072. Among climatic factors, actual evapotranspiration and precipitation were identified as the dominant influences on vegetation change in the QLM. Altitude and solar radiation had negative feedback effects on FVC , with coefficients of −0.0090 and −0.2244, respectively. Among all factors, climate exhibited a significant total effect (0.6125) on human activities.