EFFECTS OF CANOPY STRUCTURE ON GROWTH AND BELOWGROUND/ABOVEGROUND BIOMASS OF SEEDLINGS IN UNEVEN-AGED TROJAN FIR STANDS EFFECTS OF CANOPY STRUCTURE IN UNEVEN-AGED TROJAN FIR STANDS

Abstract

Growth and survival of understory seedlings are influenced 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 influences of stand basal area (BA) (m² ha^-1), photosynthetically active radiation transmitted through canopy (PAR_T), 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 were observed following five growing seasons after germination in uneven-aged Trojan fir stands. BA, PAR_T, LAI, HCB and aspect all had significant influence on the growth and belowground/aboveground biomass of understory seedlings (p<0.05). The data also showed that the light transmitted through the canopy was the most significant predictor of understory seedlings growth, thus, PAR_T reaching understory can accelerate the development of sub-canopy layers in uneven-aged Trojan fir stands. Although survival of Trojan fir 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 fir to increase a seedling’s vigor for its successful recruitment into middle and overstory. The data obtained in this study will be helpful for forest managers to enhance the establishment and recruitment of Trojan fir seedlings in uneven-aged stands