Spatiotemporal evolution and driving mechanisms of soil conservation in natural forests and plantations of the Yellow River Basin

Forest ecosystems in the Yellow River Basin play a critical role in maintaining regional ecological security and soil conservation (SC). However, the contributions of natural forests and plantations to SC, as well as the underlying mechanisms driving their variations, remain insufficiently understood. In this study, we integrated multi-source datasets, including land-use, vegetation, topographic, and climatic data, to quantify SC using the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model and investigate their driving mechanisms through spatial analysis and the Extreme Gradient Boosting–Shapley Additive exPlanations (XGBoost-SHAP) framework. The results showed that the total forest area in the Yellow River Basin increased from 7.98 × 10⁴ km² to 11.08 × 10⁴ km² between 2000 and 2020, representing an increase of 38.8%. The expansion of plantations accounted for the majority of this forest increase, however, forest type transitions may substantially alter ecosystem structure and ecological functions. SC exhibited a continuous increasing trend across the basin. The SC of natural forests increased by 17.72% during 2000–2010 and subsequently stabilized, whereas plantations showed increases of 108.95% and 54.75% during the two periods, respectively, making them the primary contributors to the overall enhancement of SC. Spatially, natural forests provided higher SC than plantations in the upper and middle reaches of the basin. In contrast, plantations exhibited greater SC than natural forests in the lower reaches, highlighting the important influence of forest type and spatial distribution patterns on ecosystem functions. Driver analysis revealed that mean annual precipitation, surface roughness, and slope were common factors regulating SC in both forest types, demonstrating the dominant roles of water availability and topographic erosion processes in shaping SC patterns. Nevertheless, distinct ecological responses were observed between forest types. Net primary productivity and tree height contributed more strongly to SC in natural forests, whereas tree height and leaf area index were the dominant drivers of SC in plantations. These findings indicate that SC in natural forests are closely associated with their long-term successional development, higher productivity, and greater structural integrity, while stand structure optimization is essential for enhancing SC capacity in plantations. Under the constraints of water availability in the Yellow River Basin, priority should be given to conserving the ecological integrity of natural forests and improving plantation ecosystem services and water-use efficiency through optimized tree species selection and stand structure management. This study provides valuable insights for ecological restoration and forest management in water-limited regions.