Stand Structure and Successional Pathway in an Artificial Hybrid Pine (Pinus × rigitaeda) Plantation from a Temperate Monsoon Region

Artificial hybrid pine (Pinus × rigitaeda) plantations, widely established in Northeast Asia for reforestation and timber production, have reached maturity, necessitating an evaluation of their ecological sustainability and successional dynamics. Although numerous studies have examined succession in pure Pinus rigida or Pinus densiflora stands, the long-term structural transition and regeneration potential of hybrid P. × rigitaeda plantations remain poorly understood. This study quantitatively assessed the successional stage and potential transition pathways of P. × rigitaeda stands using an integrated analytical framework combining vegetation classification (TWINSPAN), ordination (NMDS), successional index, survival analysis (Weibull model), and growth–environment modeling (GAM). Multi-layer vegetation data were analyzed to evaluate compositional changes, structural attributes, and nonlinear environmental responses. The results revealed that the dominance of P. × rigitaeda declined markedly while native deciduous species increased in lower strata. The Weibull survival model (k = 1.3) indicated accelerating mortality with stand aging, and the successional index showed the highest value (0.4) for Castanea crenata, followed by other Quercus species, confirming an ongoing shift toward hardwood dominance. GAM analysis confirmed that growth stability was influenced by stand age and precipitation. These findings demonstrate that P. × rigitaeda plantations are not merely artificial production forests but function as self-organizing systems facilitating natural forest recovery. In this respect, the hybrid pine plantation can be interpreted as a spontaneous ecological experiment, highlighting the restoration value of artificial hybrids as transitional stages bridging artificial afforestation and natural forest succession in temperate monsoon regions.