Submitted to: Western North American Naturalist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/22/2005
Publication Date: 1/15/2006
Citation: Denny, K.M., Sheley, R.L. 2006. Community response of non-target species to herbicide application and removal of the nonindigenous invader. Western North American Naturalist. 66(1):55-63. Interpretive Summary: Herbicides are the most commonly used to tool to manage invasive weeds. Our objective was to improve the use of herbicides by understanding how they affect plants growing in association with weeds that are considered important to the ecology of the ecosystem. We were especially interested in the herbicides impacts on broadleaved forbs. We sprayed five of the most commonly used herbicides or combinations of herbicides at three rate (high, medium, low) on native, healthy semi-arid rangeland plant communities. In nearby plots, sulfur cinquefoil was hand-pulled to determine the plants response to weed removal without the use of a herbicide. Indigenous perennial grasses increased with herbicide application, but for picloram, metsulfouron, and clopyralid grass increases were at the expense of native forbs. Hand removing sulfur cinquefoil increased total plant richness, especially that of native forbs. Restoring the species richness and diversity may be difficult using selective broadleaf herbicides because key functional groups, such as forbs, appear to be at risk.
Technical Abstract: Our main objective was to improve understanding of herbicide effects on community dynamics in order 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 low, medium and high rates of selective rangeland herbicides and that hand-removal of Potentilla recta would increase indigenous species cover, biomass and density while increasing indigenous plant species richness and diversity. Treatments consisted of three rates each of: a commercial formulation of 2,4-D+clopyralid respectively (a. 0.28 kg ai/ha + 0.0532 kg ai/ha, b. 0.56 kg ai/ha +0.1064 kg ai/ha, c. 0.84 kg ai/ha + 0.1596 kg ai/ha), 2,4-D amine (a. 0.532 kg ai/ha, b. 1.064 kg ai/ha, c. 1.596 kg ai/ha), metsulfuron (a. 0.0042kg ai/ha, b. 0.021 kg ai/ha, c. 0.032 kg ai/ha), picloram ( a. 0.14 kg ai/ha, b. 0.28 kg ai/ha, c. 0.56 kg ai/ha) and clopyralid ( a. 0.05025 kg ai/ha, b. 0.21 kg ai/ha c. 0.42kg ai/ha) and were replicated three times at two late-seral, uninfested sites in southeastern Montana. Plots were hand sprayed using a CO2 backpack spray unit applying 130 l/ha total spray volume in 1998. Potentilla recta was removed adjacent to paired non-removed control in five replicates at two sites in 1 m2 plots. Sulfur cinquefoil removal treatments were accomplished by hand pulling 100% of the sulfur cinquefoil twice during June, July, and August for two growing seasons. In 2000, canopy cover, density and biomass data were collected 24 months after initial treatment at all sites. Native perennial grass cover and biomass increased with herbicide application, however, picloram, metsulfuron, and cloypralid reduced native forb density at one site and picloram reduced forb cover at both sites regardless of rate. Effects of herbicides on species richness or diversity was not detected. Hand removing Potentilla recta increased total plant richness and, especially, that of native forbs. Restoring the species richness and diversity may be difficult using selective broadleaved herbicides because key functional groups, such as forbs, appear to be at risk.