Structure, biomass production and dynamics of four white spruce (Picea glauca [Moench] Voss) plantations near Thunder Bay, Ontario

Abstract

Stand structure, biomass production and dynamics of white spruce (Picea glauca (Moench) Voss) were investigated in four plantations, ages 4, 10, 18, and 28 years, respectively, on similar lacustrine soils. Dry matter partitioning of the white spruce component at the individual tree and stand levels and under varying densities of trembling aspen (Populus tremuloides Michx.) was analyzed. A general pattern of stand development tied to: (1) the timing and severity of site preparation preceding plantation establishment; (2) the nature and distribution of the post-cut vegetation; (3) soil and site conditions; and (4) the successional processes in the tree strata, was proposed which may also be applicable to plantations other than those in the study. Major differences in stand structure, biomass partitioning and distribution, within the white spruce populations of each plantation existed. This variation was attributed to differences in micro-site condition and the density of trembling aspen and other herbaceous vegetation surrounding the planted white spruce. Severe scarification using a modified V-plough prior to establishment of the two youngest plantations resulted in highly variable early height and diameter growth and survival of the planted white spruce. Both planted white spruce and second-growth aspen produced maximum height growth and biomass on micro-sites with deep surface horizons (Ah) where mixing of organic matter with the surface mineral soil has occurred. The presence of trembling aspen, graminoids, wild raspberry (Rubus idaeus L.), prickly rose fRosa acicularis Lindl.), and other woody tall shrubs during the stand initiation and the stem exclusion stage were correlated with the decreased height and diameter growth of the surviving planted white spruce. Total standing crop for all species and the white spruce component of the plantations each increased with plantation age; partitioning of biomass to stemwood and foliage on individual spruce trees was significantly reduced under high aspen densities and where the standing crop biomass of graminoids, herbaceous plants and woody shrubs was greatest. Spruce foliage efficiencies for wood production generally increased with stand age, decreasing aspen density and increasing dominance (crown class). A clearly defined and fully integrated biological model relating foliage efficiency of the individual white spruce growing in association with trembling aspen could not be developed. However, white spruce foliage, stemwood and total tree dry weights were explained in multiple regression models which incorporated the biomass of competing species, soil/site characteristics, and a measure of the percent cover of the spruce seedling by competing vegetation.