Juvenile growth of subalpine fir (Abies lasiocarpa) in the Montane Spruce Ecological Zone of British Columbia Canada

Subalpine fir (Abies lasiocarpa (Hook.) Nutt.) is a widely distributed western North American conifer that can grow under a wide range of light environments, initial densities and site qualities. It can be a major component of stands found within the Thompson Dry Mild variant of the Montane Spruce ecological zone (MSdm2) in the southern interior of British Columbia, Canada. In chapter 2 of this dissertation, I examined the effects of light, moisture, nutrients and neighbor density on juvenile subalpine fir growth. This led me to conclude that: 1) light availability had the largest influence on juvenile tree growth; 2) Delta-13C was the second most important growth predictor; 3) tree size also improved growth predictions; 4) soil moisture was a weak growth predictor; 5) foliar N levels did not improve growth predictions; and 6) density, as expressed as stems/ha, improved growth predictions negligibly. The results from chapter 2 helped to determine the important predictor variables (light and tree size) that were used in investigating the importance of spatially explicit competition on the development of juvenile trees (chapter 3). The chosen spatial model utilized tree size and the crowding effect of neighbors to predict juvenile radial growth. This model was then incorporated into SORTIE-ND as a new juvenile growth behavior, “Juvenile NCI Growth”, and used to test whether juvenile or mature trees have a greater competitive influence on juvenile subalpine fir growth under three basal area classes. Here, I found that juvenile radial growth was faster under the canopy of mature trees than in the neighborhood of similar sized juveniles at the two lowest density classes, 7 and 20 m²/ha. This indicated that symmetric competition processes dominated. I also found that at the highest density class, there were no differences in juvenile radial growth between the two neighbor strata. Chapter 4 was designed to test the influence of site series on growth predictions using SORTIE-ND. I found that site series did have an influence on the growth and development of the stand, as would be expected, which suggests that incorporating site quality into SORTIE-ND would improve growth and yield predictions.