Abstract: To prevent the spread of pine wilt disease caused by Bursaphelenchus xylophilus on Masson pine (Pinus massoniana), the infected trees should be removed. Clarifying the impacts of removing infected trees on stand spatial structure, understory regeneration, and community succession can provide scientific basis for ecological restoration and stand construction of Masson pine forests suffered the wilt disease. We investigated the differences in stand spatial structure, understory species composition, density, diversity, and basal diameter/height distribution across stands with varying intensities of infected tree removal (undisturbed stand (CK), light logging (I), moderate logging (II), heavy logging (III), and clearcutting (IV)). We further explored the relationship between stand spatial structure and the diversity and basal diameter/height distribution of woody plant seedlings. The results showed that stand spatial structure (except for opening degree) differed significantly among logging intensities (P<0.05). With increasing logging intensity, tree distribution became more uniform, mingling degree increased, and competition index decreased. Seedlings and saplings in the treatments CK and I had evenly distributed basal diameters and heights, whereas those in treatments II, III, and IV were concentrated in 0.15-1 cm and 0.2-1 m ranges, respectively. Seedling density in the treatment IV was significantly higher than that other stands (P<0.05), and species diversity of seedlings in CK was significantly higher than that in logged stands (P<0.05). Understory species diversity was mainly influenced by horizontal structure and competition, while seedling density was affected by competition index and opening degree. In conclusion, the removal of infected Masson pines optimizes stand spatial structure, promotes seedling-to-sapling transition, facilitates the succession of damaged Masson pine forest toward uneven-aged mixed conifer-broadleaf forests, and thereby enhances resistance to pine wilt disease. However, high-intensity logging reduces understory species diversity. Therefore, we recommend adopting moderate and dynamic thinning in early stages of infestation to get a balance between disease control and biodiversity conservation.

Key words: Pinus massoniana, infected tree removal, stand structure, regenerated seedling, species diversity