Spatial Distribution Patterns of Dominant Tree Species and Their Associations with Soil Factors in Subalpine Secondary Forests of Western Sichuan

Spatial pattern analysis is essential for understanding forest structure and successional dynamics. Focusing on natural secondary forests in the subalpine region of western Sichuan, China, we established two 1-hectare permanent plots to investigate the spatial distribution of dominant tree species and assess the soil's water-holding properties, aiming to clarify the relationship between species spatial patterns and edaphic conditions. The pioneer species <i>Betula albosinensis</i> exhibited a unimodal diameter distribution with scarce seedling presence, indicating limited regeneration. In contrast, <i>Abies fargesii</i> var. <i>faxoniana</i> showed a typical inverse J-shaped diameter distribution, suggesting stable population recruitment. At fine spatial scales, dominant species generally exhibited aggregated distributions, with <i>A. fargesii</i> var. <i>faxoniana</i> seedlings showing the strongest clumping; however, as the spatial scale increased, distributions tended toward randomness, likely due to self-thinning and density-dependent interactions. Bivariate spatial association analysis revealed that <i>B. albosinensis</i> was positively associated with <i>A. fargesii</i> var. <i>faxoniana</i> and <i>Picea asperata</i> at small scales, suggesting a potential facilitative effect of <i>B. albosinensis</i> on Pinaceae species. Moreover, capillary water-holding capacity was significantly higher in areas with greater conifer dominance, underscoring the strong environmental filtering effect of microhabitat moisture on community spatial structure. Collectively, our results suggest an ongoing mid- to late-successional shift from pioneer broadleaved to shade-tolerant conifer dominance, with concurrent changes in species composition and soil conditions. This study provides empirical insight into spatial successional processes and highlights their ecological implications for hydrological regulation in subalpine secondary forests.