Growth and survival of understory seedlings are infl uenced by their interactions with the environmental variables. The understanding of the relationships between stand density, canopy structure, and understory seedlings’ growth help forest managers conduct successful establishment through natural regeneration. In this study, the infl uence of stand basal area (BA) (m2.ha-1), photosynthetically active radiation transmitted through canopy (PART), leaf area index (LAI), height-to-crown base (HCB) and aspect on the root-collar diameter (RCD) (mm) growth, height growth (cm) and belowground/aboveground biomass (g) of seedlings is observed in uneven-aged Trojan fi r stands. Seedling growth and belowground/aboveground biomass models were developed for fi ve growing seasons after germination. PART, aspect and HCB were found to be the most strongly related to RCD and height growth of Trojan fi r seedlings. PART and aspect explained the most variance in belowground/aboveground biomass of the seedlings. The data also showed that the light transmitted through the canopy was the most signifi cant predictor of understory seedlings growth; thus, PART reaching understory can accelerate the development of sub-canopy layers in uneven-aged Trojan fi r stands. Although survival of Trojan fi r seedlings is usually high under canopy, results suggest that complete canopy closure should be avoided even in stands of shade-tolerant species such as Trojan fi r to increase a seedling’s vigor for its successful recruitment into middle and overstory. The fi ndings of this study will be helpful for forest managers to enhance the establishment and recruitment of Trojan fi r seedlings in uneven-aged stands
