Abstract: Understory vegetation plays a key role in regulating forest structure and function. To explore the effects of uneven-aged mixed silviculture on understory vegetation, we investigated species composition of understory in pure Pinus massoniana plantation (PP), uneven-aged mixed plantation (MP) of Pinus massoniana and Castanopsis hystrix (MP), and multiple species uneven-aged mixed plantation (MMP). By combining field investigations with laboratory analyses, we compared the differences in understory species composition among different forest types, and further explored the diversity of shrub and herb species in the understory, as well as the changes in functional groups and their relationships with environmental factors. We found that species richness, Shannon and Simpson indices of herb layer in MP, as well as species richness and Shannon index of shrub layer and the Shannon and Simpson index of herb layer in MMP increased significantly (P<0.05) compared with those in PP. Moreover, the species richness of the fern functional group in MP and the woody plant functional group in MMP significantly increased compared with those in PP (P<0.05). Soil NH₄⁺-N and C/P were the primary factors driving species composition of shrub layer, while slope and soil NH₄⁺-N were the primary habitat factors influencing species composition of herb layer. Additionally, soil TN was the most important habitat factor affecting plant functional groups. In summary, introducing broadleaf tree species into the uneven-aged mixed silviculture of Pinus massoniana plantations could enhance the richness and diversity of understory plants. Such changes were co-regulated by the alterations of soil properties, tree characteristics, and microenvironment under different silviculture patterns.

Key words: coniferous and broad-leaved mixed forest, understory vegetation, redundancy analysis, variance partitioning analysis