Objective Understory vegetation, as a key participant in the material cycling and energy flow of forest ecosystems, plays a significant role in understanding forest ecosystem recovery processes, biodiversity maintenance and sustainable management. Studying the impact mechanisms of logging disturbances on biomass of understory woody plants is of great importance.

Method This study focused on conifer-broadleaved mixed forests in northeastern China, employing mixed-effect models and structural equation modeling (SEM) to analyze the factors influencing biomass of understory woody plants.

Result (1) Thinning released growing space for understory woody plants, leading to a significant increase in understory biomass with higher thinning intensity (p < 0.05). (2) Understory species diversity and structural diversity were primary factors influencing understory biomass, accounting for 51.00% of the variance explained. Logging disturbance ranked second (29.48%), while the combined effects of overstory species diversity and stand structure explained 16.92%. The direct impact of light environment on understory biomass variation was minimal, explaining only 2.53%. (3) Logging disturbance significantly affected (p < 0.05) changes in tree-like shrub biomass of understory woody plants, whereas it did not significantly affect (p > 0.05) the biomass of treelets and typical shrubs. (4) SEM further revealed that logging disturbance not only directly promoted understory biomass accumulation, but also indirectly influenced it by regulating overstory stand structure and species diversity.

Conclusion This study elucidates the direct and indirect mechanisms of logging disturbance on understory biomass, highlighting central roles of understory diversity and logging intensity in enhancing biomass accumulation. These findings provide a theoretical foundation for scientifically evaluating long-term ecological effects of logging disturbance and optimizing forest management strategies, and provide a practical guidance for achieving sustainable management goals.