The combination of aminopyralid and metsulfuron is an effective post-seeding strategy to restore native grassland in Canadian Aspen Parkland

Abstract 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, Alberta, Canada, where non-native Cirsium arvense , Sonchus arvensis , and Bromus inermis dominated prior to 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 ( Rosa woodsia and Symphoricarpos occidentalis ), 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. Hesperostipa comata , Pascopyrum smithii , and Nassella viridula showed moderate establishment under treatments with aminopyralid + metsulfuron-methyl, while Festuca hallii , F. idahoensis , F. saximontana , and Koeleria macrantha 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.