Objective This paper analyzes the influence of density regulation on timber assortment structure and economic benefits of middle-aged Mytilaria laosensis plantations, so as to provide a scientific basis for management decisions.

Method Two mature M. laosensis plantations in the southern subtropical region of Guangxi, southern China, including Shaoping experimental forest, which had undergone density regulation strategy mode I (one thinning, resulting in a stem density of about 1200 plants per hectare), and the Qingshan experimental forest, which had undergone density regulation strategy mode II (three thinnings, resulting in a post-thinning stand density of 520 plants per hectare), were selected as research subjects. In each stand, 14 trees of different diameter classes were felled for stem analysis. The central sectional area formula was used to calculate the yield of each timber assortment, and the replacement cost method was employed to analyze economic benefits of different stands.

Result (1) Significant differences were observed in the non-cumulative yields of small- and medium-diameter timber between mode I and mode II (P < 0.05). (2) From the 25th year, the cumulative yield of small-diameter timber in mode II was lower than in mode I. From the 21st year, the cumulative yields of medium- and large-medium-diameter timber in mode II were higher than in mode I, although these differences were not statistically significant (P > 0.05). (3) The cumulative yield patterns of different timber assortments in mode I and mode II stands exhibited similar trends. Specifically, the cumulative yield of small-diameter timber increased with age, then slightly decreased, and finally tend to stabilize. The cumulative yield of medium-diameter timber increased with age, then stabilized. The cumulative yields of large- and large-medium-diameter timber increased with age. (4) For the production of small and medium-diameter wood, the optimal rotation period for mode I was 17−19 years, and for mode II, it was 17−21 years. The economic benefits between the two modes were not significantly different. However, when the primary objective was the production of large-medium-diameter wood, from the 23rd year onwards, the dynamic economic benefits of mode II were significantly higher than those of mode I (P < 0.05). The rotation period for mode II should ≥ 26 years.

Conclusion The density regulation measures of mode I and mode II do not significantly affect the cumulative yield and static economic benefits of different timber types in M. laosensis plantations. However, their impact on dynamic economic benefits is significant. The optimal management strategy for maximizing dynamic economic benefits in M. laosensis plantations for both mode I and mode II is to produce small and medium-sized timber. There is no significant difference in economic benefits between the two modes under this strategy. When the management goal shifts to producing large and medium-sized timber, the dynamic economic benefits of both modes decrease significantly with the increase in stand age. The mode I stands will incur losses, while mode II can still maintain a good level of profitability.