Understory Plant Diversity Dynamics During Post-Fire Recovery of Pinus massoniana Plantations: Effects of Stand Age

This study investigates the effects of stand age on understory plant diversity in Pinus massoniana plantations recovering from fire disturbance, aiming to provide scientific references for urban ecological restoration and forest management. Three stand ages (15, 30, and 60 years) of P. massoniana plantations in Huangfushan National Forest Park, Chuzhou City, China, were selected as research objects. By combining α and β diversity indices with analyses of edaphic factors from different soil layers, we examined understory plant diversity and its influencing factors across different stand ages. Stand age significantly shaped shrub and herb richness and Shannon–Wiener diversity, which peaked in 15-year-old stands. Symplocos tanakana dominated the shrub layer throughout succession, while the herb layer shifted from single- to multi-species dominance; the Godron structural stability index increased with stand age. Soil C, N, and organic matter responded to stand age, soil layer, and their interaction, whereas pH and bulk density showed partial responses. Understory diversity was negatively correlated with 0–10 cm soil C and organic matter, and herb diversity was positively correlated with 20–30 cm soil N. Herb-layer composition was significantly associated with shallow-soil pH, bulk density, and C/N ratio, whereas no soil drivers were detected for the shrub layer. In summary, this study systematically reveals the synergistic evolution of understory plant diversity and soil characteristics in P. massoniana plantations at different stand age stages, providing an important basis for scientific management and sustainable development of plantations.