Objective Forest structure plays a crucial role in tree growth and stability. Analyzing the impact of transformation practices on the structure of Pinus massoniana forests can provide theoretical reference for forest quality improvement and sustainable management.

Method Different transformation treatments of secondary P. massoniana forests, including light thinning without replanting (LTNP), moderate thinning without replanting (MTNP), heavy thinning without replanting (HTNP), moderate thinning with broadleaf replanting (MTP), heavy thinning with broadleaf replanting (HTP), and clear cutting with broadleaf replanting (CCP) were selected as research objects in Jiande County, Zhejiang Province of eastern China. We explored the effects of thinning and replanting on both spatial and non-spatial stand structures, and provided comprehensive evaluation of stand structure under different transformation treatments.

Result (1) Thinning and broadleaf replanting significantly altered the forest species composition. With the increasing of thinning intensity, tree species diversity initially increased and then decreased. The DBH structure of stand changed from “single peak” to “multi-peak”. The proportion of small or medium diameter trees raised and non-replanted stands had a higher proportion than replanted stands under same thinning intensity. (2) In terms of space structure, the uniform angle index of CCP was significantly lower than that of other transformation types, and the mingling degree of LTNP was markedly lower compared with others. As thinning intensity increased, stand openness gradually increased, the forest layer index initially increased and then decreased. Additionally, both the dominance and competition index gradually decreased, and these two indexes were lower in broadleaf-replanted stands than in non-replanted ones under the heavy thinning intensity. (3) The rank of comprehensive evaluation value of stand structure was MTP > HTNP > CCP > HTP > MTNP > LTNP.

Conclusion After moderate thinning and widening of Pinus massoniana (e.g., Cinnamomum chekiangense, Phoebe chekiangensis), the overall forest structure was significantly optimized, which plays an important role in promoting the transition of pure Pinus massoniana forests to mixed coniferous and broadleaved forests. This study provides theoretical reference for the sustainable management of Pinus massoniana forest.