Interactive Effects of Soil Properties and Species Richness on Community Stability Along Tibetan High-Altitude Road Slopes

To better understand restoration processes on the plateau, we assessed plant diversity and community stability in restored roadside patches dominated by herbs (H), shrubs, and herbs (SH), or trees, shrubs, and herbs (TSH) at four elevations (3100, 3300, 3500, and 3800 m a.s.l.). We examined how vegetation configuration, altitude, climatic conditions, topography, and soil properties were associated with plant diversity and community stability. Vegetation configuration and altitude significantly affected plant diversity, with mixed vegetation patches generally supporting greater diversity below 3300 m, whereas herb-dominated patches performed better at higher elevations. Nested composite structural equation modelling indicated that soil properties were important predictors of alpha diversity and were themselves associated with altitude. Community stability increased with species richness at lower richness levels but declined after a threshold, consistent with a shift from complementarity to stronger interspecific competition under resource limitation. Mantel and RDA analyses indicated that dissolved organic carbon (DOC) was closely associated with herb-layer diversity, whereas total potassium and available phosphorus were important for shrub and tree layers. Soil water content (SWC), available potassium (AK), and DOC were negatively associated with community stability. Together, these findings highlight the importance of site-specific species selection and coordinated soil management for restoring and stabilizing high-altitude roadside vegetation.