Growth Increment Tree Height Ratios
Data analysis was completed for trees from the lower foothills and for the central mixedwoods. Results were summarized between species (white spruce and trembling aspen) and within species for white spruce in the lower foothills natural subregion.
Growth increment tree height ratios were calculated for both white spruce and trembling aspen seperately. Figure 3 shows the growth increment tree height ratios for white spruce and trembling aspen in the central mixedwoods. The ratios are very close in the central mixedwoods. The lower foothills data (Figure 4) showed some separation between white spruce and trembling aspen from age 5 onward.
Trees in the lower foothills sample were selected by four canopy position classes which included dominant, co-dominant, intermediate and suppressed. The following graph (Figure 5 ) shows a very small diference beteween growth increment tree height ratios between trees selected from different canopy positions.
The growth increment tree height ratio was greatest for white spruce and trembling aspen up to 7 meters and then converged in the central mixedwoods (Figure 6). In the lower foothills they diverged at 4 meters and then white spruce ratio became greater than the trembling aspen. This is probably due to white spruce being an understory species and accelerating growth to keep up with the trembling aspen.
A comparison was made of the variance using a boxplot for both white spruce and trembling aspen in lower foothills. The graphed values were based on the functions used to calculate the growth increment tree height ratios. Figure 7 indicates that the ratios are close but still statistically different. The graph indicates that the growth increment tree height ratio was greater for the white spruce rather than the trembling aspen.