Productivity of aspen stands with and without a spruce understory in Alberta's boreal mixedwood forests

In northeastern Alberta, the current biomass and periodic annual biomass increment (PAI) was measured in 29 stands of maturing aspen (Populus tremuloides)-white spruce (Picea glauca), aged 48 to 105 years. Plots in pure aspen were paired with nearby plots of aspen growing on a similar landform but with a spruce understory. Biomass was estimated by diameter at breast height and allometric equations. Totalled over both species, there was 10.5% greater PAI and 10.0% greater biomass in the mixed plots than in the pure aspen plots. Pure aspen plots, however, had 12.9% greater aspen biomass and 25.2% greater aspen PAI than the aspen component of mixed plots. The apparent decline in productivity of aspen in the mixed stands, however, could not be related to the variation in spruce abundance in these mixed stands.