ARS | Publication request: Fire and nitrogen effects on purple threeawn invaded plant communities

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: September 14, 2012
Publication Date: N/A

Technical Abstract: Purple threeawn (Aristida purpurea) is a native grass capable of rapidly increasing on rangelands, where it forms near monocultures, and alters succession. 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) assess prescribed fire and nitrogen additions as successional stimulants on purple threeawn invaded landscapes, and 2) explore vegetation management strategies appropriate for reducing purple threeawn. Season of fire (summer, fall, no fire) and different levels of nitrogen (0, 46, 80 kg N•ha-1) were factorially arranged in a completely randomized design in southeastern Montana in different years at different sites. We measured peak biomass one year post-treatment at both sites and two years post-treatment at Site 1. Initial purple threeawn biomass at both sites was 1214±46 kg•ha-1. One year following fire, total purple threeawn biomass was reduced 91% and 79% by summer and fall fire, respectively. This trend continued when fire effects on current year purple threeawn production were assessed. Nitrogen additions did not alter purple threeawn biomass at either site. C3 perennial grass at Site 1 doubled with nitrogen additions and was not impacted by fire. Nitrogen additions and fire had no affect on C3 perennial grass at Site 2. Two years post-fire purple threeawn showed no increase in production at Site 1 and C3 perennial grass biomass was greatest in plots with nitrogen additions. Prescribed fire during the summer appears to be the best method for reducing purple threeawn production.