Our main objective was to improve understanding of herbicide effects on community dynamics to refine the use of technology and advance the development of ecologically based weed management strategies. We hypothesized that native grasslands would exhibit reductions in culturally sensitive forb cover, biomass, and density relative to the rate of application of selective rangeland herbicides, and that hand-removal of sulfur cinquefoil (Potentilla recta L.) would increase indigenous species cover, biomass, density, species richness, and diversity. Treatments consisted of 3 rates each of 2,4-D clopyralid (0.28 kg ai · ha−1 0.0532 kg ai · ha−1, 0.56 kg ai · ha−1 0.1064 kg ai · ha−1, 0.84 kg ai · ha−1 0.1596 kg ai · ha−1); 2,4-D amine (0.532 kg ai · ha−1, 1.064 kg ai · ha−1, 1.596 kg ai · ha−1); metsulfuron (0.0042 kg ai · ha−1, 0.021 kg ai · ha−1, 0.032 kg ai · ha−1); picloram (0.14 kg ai · ha−1, 0.28 kg ai · ha−1, 0.56 kg ai · ha−1); and clopyralid (0.05025 kg ai · ha−1, 0.21 kg ai · ha−1, 0.42 kg ai · ha−1). This experiment was replicated 3 times at 2 late-seral, noninfested sites in southeastern Montana. In a companion study, sulfur cinquefoil was removed adjacent to paired nonremoved controls in 5 replicates at 2 sites in 1-m2 plots for 2 growing seasons. Canopy cover, density, and biomass were collected 24 months after initial treatment at all sites. Indigenous perennial grass cover and biomass increased with herbicide application; however, picloram, metsulfuron, and clopyralid reduced native forb density at 1 site, and picloram reduced forb cover at both sites regardless of rate. Effects of herbicides on species richness or diversity were not detected. Hand-removing sulfur cinquefoil increased total plant richness, especially that of native forbs. Restoring species richness and diversity may be difficult using selective broadleaf herbicides because key functional groups, such as forbs, appear to be at risk.
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