Natural Forests Accelerate Soil Hydrological Processes and Enhance Water-Holding Capacities Compared to Planted Forests After Long-Term Restoration

Abstract

Understanding the impacts of afforestation practices on water resources is essential for sustainable land management in water-limited ecosystems. However, the over decades long-term effects of vegetation restoration on soil hydrological processes and water-holding capacity remain poorly understood. In this study, we conducted field monitoring during 2006–2024 in a typical catchment on the Loess Plateau, and systematically monitored soil hydrological processes, soil water-holding capacities, soil properties (0–180 cm), and vegetation attributes (across the tree, shrub, and herbaceous layers) of four vegetation types: planted Pinus tabuliformis forest, planted Platycladus orientalis forest, planted Robinia pseudoacacia forest, and natural secondary forest. The results indicate that natural secondary forests outperform planted forests in soil hydrological properties. Specifically, secondary forests show 68.7% more macroporosity, 13.7% larger mean equivalent diameter, and 8% higher soil moisture compared to planted forests. They also have 34.2% higher saturated hydraulic conductivity and enhanced soil organic carbon (SOC), field capacity, and available water content. Long-term trends (18-year) reveal that secondary forests maintain higher soil water content and exhibit faster soil hydrological processes, particularly in precipitation redistribution, with higher water conversion into soil water storage. Mantel test and structural equation modeling reveal that soil properties (e.g., bulk density and SOC) and understory diversity are key influencing factors on soil hydrological processes and water-holding capacities, indicating that natural regeneration promotes a more optimal ecosystem structure. These findings highlight the resilience of naturally regenerated ecosystems in conserving water resources, regulating hydrological processes and sustaining water resources during afforestation efforts on the Loess Plateau.