Thinning effects vary depending on thinning type, intensity, and timing, making it important to compare alternative scenarios before field implementation. We aimed to provide a fundamental basis for selecting appropriate thinning operations by analyzing changes in stand structure and competition release effects under different thinning regimes using LiDAR-based thinning simulations. Specifically, we quantitatively evaluated how the competition releases effect of row thinning varied with the spatial position of residual trees. Among the stand structural variables, significant differences among thinning types were observed only for tree height. Quantitative thinning resulted in a relatively uniform structure dominated by upperstory trees, whereas row thinning retained trees across a relatively wide range of height classes. The reduction in the mean competition index of residual trees ranged from approximately 14.9% to 67.3% depending on thinning type. Quantitative thinning showed greater competition-reduction efficiency relative to the tree removal rate, whereas some row thinning types achieved competition reduction and total harvest volume comparable to those of quantitative thinning. However, the competition-reducing effects of row thinning were concentrated among residual trees adjacent to cutting rows, indicating that the spatial positions of residual trees should be considered when evaluating row thinning effects. Overall, thinning methods should be selected by considering not only predicted long-term growth and volume changes but also stand-management objectives and the operational efficiency associated with each thinning approach.

This research aimed to provide fundamental growth data to support efficient afforestation and forest management, analysing the early growth of Korean red pine (Pinus densiflora Siebold & Zucc.) and Japanese larch (Larix kaempferi (Lamb.) Carr.) at varying planting densities in Korean slope plantation forests (30%–35% slope). Therefore, P. densiflora and L. kaempferi (both 2-year-old (1 + 1) seedlings) were planted in the Gwangneung Experimental Forest, Korea in April 2020, according to three different densities (i.e., P. densiflora: 2500, 3000 and 5000 trees ha⁻¹; L. kaempferi: 2000, 2500 and 3000 trees ha⁻¹). The highest net diameter at breast height (DBH) growth and DBH class (8 cm) of P. densiflora were observed at 2500 and 3000 trees ha⁻¹ groups, while the highest net DBH growth and DBH class (>5 cm) of L. kaempferi trees were observed at 2000 trees ha⁻¹ group. Meanwhile, the planting density of 3000 trees ha⁻¹ did not affect the reduction in the net growth of DBH and stem volume in P. densiflora. Conversely, the net growth of stem volume in L. kaempferi was the lowest in the 2500 trees ha⁻¹ group rather than the 3000 trees ha⁻¹ group. This study indicates that the lowest or highest density does not always equate to the highest or lowest stem volume obtainment and provides useful information for initial setup and optimal density when planting two different species, P. densiflora and L. kaempferi afforestation. Results can be utilized to support the planning of post-reforestation management.