Spatiotemporal vegetation greenness dynamics in China's steppe ecosystems and the modulating roles of biotic, climatic, soil, topographic, and grazing drivers.

Steppe ecosystems provide vital ecosystem services but have undergone widespread degradation. Quantifying vegetation greenness dynamics and their drivers is therefore essential for evaluating ecological restoration. Here, we assessed spatiotemporal changes in vegetation greenness across China's steppe ecosystems using the kernel normalized difference vegetation index (kNDVI). Multi-source remote-sensing and gridded datasets were integrated with trend analysis, XGBoost-SHAP, and piecewise structural equation modeling (piecewiseSEM) to identify vegetation greenness patterns, key drivers, and their interaction pathways. The results showed a significant increase in kNDVI across China's steppe ecosystems from 2001 to 2023, with a mean growth rate of 0.5 × 10-3 yr-1 and improvement across 81.8% of the study area. Relative to the mean kNDVI of 0.033, this trend represents a cumulative increase of approximately 34.8% over the study period. As the proximate drivers of kNDVI growth, biotic factors accounted for 55% of the total relative importance, followed by climatic (23%) and soil (15%) factors. Notably, the positive effects of biotic factors were significantly mediated by indirect climatic and soil pathways, with standardized effect sizes of 0.32 and 0.41, respectively. Additionally, we emphasize that conservation strategies should be tailored to specific steppe subtypes, offering critical guidance for site-specific management to sustain ecosystem health and resilience. These findings enrich the understanding of large-scale spatiotemporal dynamics in China's steppe ecosystems, providing a scientific basis for restoration planning and adaptive management to enhance long-term ecosystem resilience.