Early Tree Growth Performance Under Different Planting Density Tactics in Pinus densiflora Siebold & Zucc. and Larix kaempferi (Lamb.) Carr

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.