The potential for use of a partial canopy for controlling growth ofCalamagrostiscanadensis(Michx.)•Beauv., andEpilobiumangustifoliumL. among regeneratingPiceaglauca(Moench) Voss saplings was assessed in the understory of 24 established stands in theP.glauca–Viburnum–Rubuspubescensassociation of the lower boreal cordilleran ecoregion of Alberta. Stand overstories were dominated byPopulustremuloidesMichx.,P.glauca, or were a mixture of these two species The composition, basal area, and light transmission of the overstory of each stand were measured. Hardwood-dominated overstories transmitted between 14 and 40% of incoming light whileP.glaucacanopies transmitted between 5 and 11 % of light. Cover and height ofC.canadensisandE.angustifoliumdecreased with decreasing light transmission; at 40% light, both species were greatly reduced compared with open-grown conditions and both were virtually eliminated from stands with less than 10% light. The annual height increment ofP.glaucasaplings increased from 5 cm at 10% light to 25 cm at 40 % light; the latter increment was approximately equal to growth in 100% light conditions. The number of buds, the diameter of the current leader, and the height to diameter ratio of the tree also increased with light transmittance.