Modeling growth of understory aspen and spruce in western boreal Canada

For aspen and spruce in western sub-boreal and boreal Canada this study investigated regional variation in: (1) species-specific crown openness for mature trees, and (2) light-growth relationships for juvenile trees.; Regional variation in species-specific crown openness was found for both species, but the magnitude of the variation was judged to only cause small variation in understory light levels.; Regional variation in the light-growth relationship was found for both species but no indications of shifts in the successional dynamics between the two species were observed.; The regional variation in the two investigated quantities did not follow the same regional pattern and their combined effect cannot be expected to strengthen regional differences in understory tree performance.; The regional shapes of the light-growth relationship were similar for the two species. The main observed difference between the two species was the initial fast growth of aspen.; For spruce in aspen-dominated areas of the boreal mixedwood region, asymptotic light growth relationships were found. In western conifer-dominated regions, approximately linear light-growth relationships were observed. This regional variation was best explained by the different effect of aspen-dominated and conifer-dominated canopies on the light-growth relationship. It is hypothesized that the different effects of canopy-type can be caused by several effects, including nutrient availability, soil temperature, and leaf-off period.; The findings of this study were incorporated in the stand level simulation model SORTIE-ND. An evaluation of SORTIE-ND illustrated that the model generally produces realistic predictions and can be considered as a management tool. A comparison of model predictions with permanent plot data for mixed stands in the Sub-Boreal Spruce Zone of British Columbia indicated that the model has problems with prediction of aspen mortality rates and tends to overestimate growth rates especially for spruce.