Within-Crown Distribution Patterns of White Spruce in Pure Composition and in Mixture with Trembling Aspen

The purpose of this investigation was to examine the effects of species composition and crown section on within-crown foliage distribution and the relationship of basal area growth rate to amount of foliage on young white spruce (Picea glauca) growing in pure composition and in mixture with trembling aspen (Populus tremuloides). Branch and needle biomass, projected leaf area, specific leaf area, and ratio of needle biomass to branch biomass, along with several whole-tree metrics, including height and diameter at breast height (1.3 m), were measured on thirteen 20-y-old white spruce trees, 7 from pure composition and 6 from mixed composition. While there was no effect of composition on whole-tree differences among subject trees, within-crown distribution of branch and foliage amount and morphology and concentration of foliage were significantly affected by both composition (mixed and pure) and crown section (lower, mid, upper). There was a positive relationship between periodic annual basal area increment and foliage amount (biomass and projected area) on subject white spruce trees that did not differ between trees in pure and mixed compositions. Despite the significant effect of species composition on the vertical within-crown distribution of foliage and branch amount and foliage morphology, similar changes in total foliage biomass and area had similar effects on periodic annual increment of basal area regardless of composition.