The understory plant community of 63 boreal mixedwood stands in southeastern Manitoba, Canada, that were disturbed in the 1980s (21 by crown fire, 20 by logging, and 22 by severe spruce budworm ( Choristoneura fumiferana ) outbreak) were investigated. Understory plant communities that developed after fire, logging, and spruce budworm outbreak shared a large number of species (47 out of 81 identified). However, compared with fire and spruce budworm outbreak, logging promoted the rapid expansion of tall shrubs (52.7% vs. 17.2% and 29.75% coverage, respectively), particularly Corylus cornuta . Significant differences were also found between disturbance types when species coverage was compared on the basis of shade tolerance and regeneration strategy. Lower shrub coverage following fire is attributed to greater disturbance severity on the forest floor, affecting in situ propagules and competition from dense trembling aspen ( Populus tremuloides Michx.) regeneration. Lower shrub coverage following spruce budworm outbreak is attributed to slow opening of the canopy coupled with retention of a residual canopy of nonhost trees. Uniformly high shrub coverage following logging resulted in less heterogeneity and lower species diversity at both the stand and the disturbance level compared with natural disturbances. High shrub coverage may negatively impact conifer recruitment and have significant implications for future stand composition and productivity. Consideration of a natural insect outbreak model, rather than fire, for management of boreal mixedwood stands is recommended, particularly if stands are to be left to regenerate naturally.

Mineral soils exposed by fire are often covered by a layer of ash due to complete consumption of the forest floor (litter and duff). To assess the possible effects of ash on seed germination and viability of jack pine ( Pinus banksiana Lamb.), black spruce ( Picea mariana (Mill.) Britton, Sterns, Poggenb.), white spruce ( Picea glauca (Moench) Voss), and balsam fir ( Abies balsamea (L.) Mill.), a laboratory experiment was conducted using ash derived from three types of forest floor samples. The samples represented areas of high conifer concentration, high aspen concentration, and mixed aspen and conifer and were collected from five mature aspen ( Populus tremuloides Michx.) – conifer mixedwood stands in southeastern Manitoba. Ash derived from each forest floor type neither prohibited nor delayed conifer germination, except that of balsam fir. Balsam fir had significantly less germination on ash derived from forest floor samples with high aspen concentration. When corrected for seed viability, balsam fir had significantly less germination on all three ash types compared with jack pine, black spruce, and white spruce. However, the impact of ash on balsam fir is unlikely to have meaningful ecological implications, as balsam fir is a climax species and will establish in undisturbed mature forests.