Abstract
BACKGROUND: Natural regeneration is pivotal for sustaining evolutionary processes in plant species. Identifying determinants that shape recruitment dynamics could elucidate key factors governing this critical biological process. However, the relationship between environmental variables and recruitment patterns in Fagus hayatae remains uninvestigated, despite its dual significance as a species endemic to China and a National Grade II Protected Plant. This knowledge gap persists even though understanding such ecological interactions could enhance conservation management for this vulnerable endemic tree species. METHODS: This study employed Pearson correlation analysis, redundancy analysis (RDA), and structural equation modeling (SEM) to examine environmental factors of natural regeneration in Fagus hayatae populations across ontogenetic stages (seedling, sapling, small tree) within three stratified elevational bands (low: 1,670-1,700 m; mid: 1,770-1,800 m; high: 1,890-1,940 m) of Micangshan Nature Reserve, located in Sichuan Province, China. CONCLUSIONS: Structural equation modeling (SEM) revealed altitude-specific environmental regulation of Fagus hayatae regeneration dynamics. In low-altitude stands (1,670-1,700 m), the litter layer emerged as the primary limiting factor for seedling density (direct effect: -0.80), while diameter at breast height (DBH) suppressed sapling density through direct negative pathways (-0.63). Soil pH exhibited indirect positive mediation on seedling establishment via litter layer modification (0.42), suggesting synergistic management of litter removal and soil acidity regulation enhances regeneration success. Mid-elevation populations (1,770-1,800 m) demonstrated contrasting dynamics: DBH positively influenced sapling density (0.57), small tree density (0.89), and height growth (0.38), whereas available potassium indirectly reduced regeneration capacity through cascading effects involving canopy structure (DBH-mediated) and soil moisture, necessitating balanced canopy light penetration and weak acidic pH maintenance. High-altitude ecosystems (1,890-1,940 m) exhibited distinct nutrient-temperature synergies: available potassium exerted the strongest direct positive effect on small tree density (0.70), while air temperature (0.58) and litter thickness (0.53) jointly promoted vertical growth, highlighting the dual importance of organic layer preservation and thermal constraint mitigation in alpine forest regeneration. These findings delineate elevation-dependent multifactorial interaction networks governing Fagus hayatae population dynamics, establishing mechanistic frameworks for natural regeneration prediction while informing altitude-specific silvicultural interventions to optimize conservation outcomes.