Experimental study on different afforestation densities of Cunninghamia lanceolata var. Luotian

This study aimed to investigate the effects of planting density on the early growth of Cunninghamia lanceolata var. Luotian plantations, thereby providing a basis for density regulation in targeted cultivation. A 6-year-old. Cunninghamia lanceolata var. Luotian plantation in Xianning City, Hubei Province, was selected as the research subject. Growth indicators, including mean diameter at breast height (DBH), mean tree height, individual tree volume, stand volume, and competition index, were continuously monitored for four years under four planting densities (3,704, 4,444, 6,667, and 10,000 trees/hm²). A linear mixed model was employed for two-way repeated-measures ANOVA to analyze the interactive effects of stand age and density on growth dynamics. The results showed that mean DBH and individual tree volume decreased significantly with increasing density, whereas stand volume increased significantly. Significant interactive effects between density and stand age were detected for DBHand individual tree volume, indicating that the inhibitory effect of density on individual growth intensified with increasing stand age. No significant interactive effect was found for tree height (P> 0.05). At age six, the stand with the lowest density (3,704 trees/hm²) achieved the maximum values for mean DBH (8.9 cm), mean tree height (7.1 m), and individual tree volume (0.021 8 m³), which were significantly higher than those in stands with densities of 6,667 and 10,000 trees/hm². Conversely, the stand with the highest density (10,000 trees/hm²) yielded the maximum stand volume (107.063 1 m³/hm²), which was significantly greater than that of the other stands. The current annual increment of all growth indicators initially increased and then decreased with stand age for all stands. The proportion of trees in smaller diameter classes, cumulative percentage of diameter classes and height classes, and competition index all increased with increasing planting density. Planting density significantly influences both stand-level and individual tree growth in Cunninghamia lanceolata var. Luotian plantations, and the density effect intensifies with stand age. Given its strong early-age fast-growing trait, suitable planting density should be selected based on cultivation objectives: a high-density model (10,000 trees/hm²) is recommended for small-diameter fast-growing timber production, whereas a lower density (3,704～4,444 trees/hm²) is suggested for medium- to large-diameter timber production, with timely thinning for high-density stands.