Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 12, 2013
Publication Date: September 1, 2013
Repository URL: http://handle.nal.usda.gov/10113/59334
Citation: Strong, D.J., Vermeire, L.T., Ganguli, A.C. 2013. Fire and nitrogen effects on Purple Threeawn abundance in northern mixed-grass prairie old fields. Rangeland Ecology and Management. 66:553-560. Interpretive Summary: Purple threeawn (Aristida purpurea Nutt. varieties) is a native grass capable of rapidly increasing on rangelands, forming near monocultures, creating a stable state. Rangelands throughout the Great Plains and Intermountain West have experienced increases in purple threeawn abundance, leading to reductions in overall forage quality and community diversity. Our objectives were to: 1) examine prescribed fire and nitrogen as tools to shift species composition in a purple threeawn invaded community, 2) reveal vegetation management strategies appropriate for reducing purple threeawn abundance. Fire reduced purple threeawn abundance one-growing season post-fire, with sustained reductions two-growing seasons post-fire. Nitrogen had no effect on purple threeawn abundance. Summer prescribed fire appears to be the best management tool to reduce purple threeawn abundance.
Technical Abstract: Purple threeawn (Aristida purpurea Nutt. varieties) is a native grass capable of increasing on rangelands, forming near monocultures, and creating a stable state. Productive rangelands throughout the Great Plains and Intermountain West have experienced increases in purple threeawn abundance, reducing overall forage quality. Our objectives were to 1) reveal the effects of prescribed fire and nitrogen amendments on purple threeawn abundance and 2) assess non-target plant response post-treatment. Season of fire (no fire, summer fire, fall fire) and nitrogen addition (0, 46, 80 kg N • ha-1) were factorially arranged in a completely randomized design and applied to two similar sites in southeastern Montana. We evaluated fire and nitrogen effects on purple threeawn basal cover, relative composition, and current-year biomass one growing season post-fire at two sites treated during different years. Post-fire spring weather post-fire was very different between years, impacting community response. Initial purple threeawn biomass at both sites was 1214 ± 46 kg • ha-1. When post-fire growing conditions were wet, current-year biomass of purple threeawn was reduced 90 and 73% with summer and fall fire, respectively. Under dry post-fire growing conditions, purple threeawn current-year biomass was reduced 73 and 58% with summer and fall fire, respectively. Nitrogen additions had no effect on purple threeawn current-year biomass at either site. C3 perennial grass current-year biomass doubled with nitrogen additions and was not impacted by fire during a wet spring. Nitrogen additions and fire had no effect on C3 perennial grass current-year biomass following a dry spring. Prescribed fire appears to be a highly effective tool for reducing purple threeawn abundance on semi-arid rangelands.