Soil evolution and driving factors in Pinus tabuliformis forests of the Loess Hilly Region

Understanding the long-term interactions between vegetation restoration and soil evolution is critical for ecological management in degraded regions. This is particularly urgent in the Loess Hilly Region, where severe soil erosion threatens ecosystem sustainability. However, key knowledge gaps remain regarding how soil indicators co-evolve with biotic communities during prolonged restoration. This study assesses soil physicochemical indicators, faunal communities, and herbaceous dynamics across a 1- to 22-year chronosequence of Pinus tabuliformis forests in Wuqi County's Loess Hilly Region, with pre-afforestation (PRG) and 22-year natural grasslands (AG) as controls. The results revealed, as restoration progressed, the interconnections among soil indicators strengthened, resulting in more cohesive and robust network structures. In contrast, the network structure of grasslands became increasingly fragmented over time. Soil fauna significantly influenced Saturated water content, Capillary porosity and Total nitrogen in the early stages of Pinus tabuliformis forest restoration; however, this influence gradually diminished. Conversely, the contribution of the Margalef richness index of herbaceous communities increased over time. In grasslands, the Margalef richness index and the Pielou evenness index of soil fauna significantly affected soil physicochemical indicators. Restoration duration positively influenced soil quality index, total carbon pool, electrical conductivity, and organic matter, with the most pronounced effects on soil physical indicators (Total porosity and Electrical Conductivity) and fauna diversity. However, the path coefficient of restoration duration on HR was -0.31, indicating a negative impact on herbaceous community richness. These findings provide valuable data and a theoretical foundation for assessing ecological benefits and guiding high-quality development in long-term vegetation restoration practices in the Loess Hilly Region.