Patterns of moss and liverwort species diversity — species richness and species turnover (β-diversity) — in three conifer-dominated boreal forest stands of northern Alberta, Canada are described. We examined the relationship between bryophyte species diversity and micro-environment at two sample grains, the microsite — substrate types for moss colonization: logs, stumps, tree bases, undisturbed patches of forest floor (dominated by feather moss species), and disturbed patches of forest floor — and the mesosite (25 m × 25 m plots). Microsite type and properties (e.g. decay class, hardwood vs softwood, pH) were the principal predictors of bryophyte species diversity and not micro-environment variation among mesosites. Microsite type was the strongest predictor of microsite species richness and β-diversity was higher among microsites and types and within microsites than among mesosites or stands. Microsite properties were significant predictors of species richness for all microsite types. Log and stump decay classes, influenced also by hardwood vs softwood predicted species richness of woody microsite types and soil pH and moisture predicted species richness of forest floor microsites. β-diversity was highest for tree bases and disturbed patches of forest floor and lowest for logs. Mesosite β-diversity was lower than that among microsites, and mesosite species richness was not well explained by measured environmental parameters. Results suggest that in conifer-dominated boreal stands, species richness of microsites is only negligibly influenced by within-stand variation at the mesosite grain and that substrate characteristics are the most important predictors of bryophyte species diversity in this ecosystem.