Post-seeding vegetation management is critical for restoring grasslands dominated by invasive species, yet few studies have evaluated these strategies in the Aspen Parkland ecoregion. We tested the effects of no treatment (Control), mowing-only (Mow), herbicide-only (Herbicide; aminopyralid 52.5% + metsulfuron-methyl 9.45% at 230 g ai ha−1), and mowing and herbicide application (Combination) on plant community composition, diversity, and biomass over two growing seasons following seeding of seven cool-season native grass species. The study was conducted on a disturbed site in Edmonton, AB, Canada, where non-native Canada thistle [Cirsium arvense (L.) Scop.], field sowthistle (Sonchus arvensis L.), and smooth brome (Bromus inermis Leyss.) dominated before treatment. Treatments with aminopyralid + metsulfuron-methyl (aminopyralid + metsulfuron-methyl alone and Combination) significantly reduced noxious and introduced species richness and cover (P < 0.001), eliminated forbs, and shifted plant composition toward greater dominance by seeded and native grasses. However, these treatments also eliminated native shrubs [Woods’ rose (Rosa woodsii Lindl.) and western snowberry (Symphoricarpos occidentalis Hook.)], reduced litter biomass, and increased bare ground. The Mow treatment maintained high species richness and forb biomass, with noxious and introduced species remaining dominant and seeded species establishment improving slightly relative to the control. Despite differential species responses, overall seeded species richness, diversity, and cover did not differ significantly among treatments. Needle and thread grass [Hesperostipa comata (Trin. & Rupr.) Barkworth], Western wheatgrass [Pascopyrum smithii (Rydb.) Á. Löve], and green needle grass [Nassella viridula (Trin.) Barkworth] showed moderate establishment under treatments with aminopyralid + metsulfuron-methyl, while Plains rough fescue [Festuca hallii (Vasey) Piper], Idaho fescue (Festuca idahoensis Elmer), Rocky Mountain fescue (Festuca saximontana Rydb.), and June grass [Koeleria macrantha (Ledeb.) Schult.] established less in any treatment. Community composition diverged most between treatments with aminopyralid + metsulfuron-methyl and the Control treatment. These results highlight trade-offs between invasive species control and impacts on non-target natives and ecosystem function. Among the treatments, aminopyralid + metsulfuron-methyl alone provided the most balanced outcome, suppressing invasive species while minimizing soil disturbance and improving seeded grass recruitment. This study highlights the importance of integrating vegetation treatments with species-specific seeding when restoring heavily invaded grasslands in the Aspen Parkland.
