Title: Fire and nitrogen effects on purple threeawn invaded plant communities Authors
Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: December 1, 2011
Publication Date: January 28, 2012
Citation: Strong, D.J., Vermeire, L.T., Ganguli, A.C. 2012. Fire and nitrogen effects on purple threeawn invaded plant communities. Society for Range Management Meeting Abstract #0117. Interpretive Summary: Currently, 60-70% of the total botanical composition on our research site is comprised of A. purpurea, and it is believed that succession has been arrested in areas dominated by this grass. In order to release succession, we propose to use fire and nitrogen addition as successional “stimulants”. Due to A. purpurea’s hemicryptohyte growth form (Raunkinauer 1934) and the location of its meristems, we hypothesize that A. purpurea biomass can be reduced with prescribed fire. This hypothesis was strengthened by research conducted on A. purpurea in Texas (Trlica Jr. and Schuster 1965). The relationship between nitrogen and A. purpurea is currently poorly understood and warrants further investigation. Pre-treatment soil tests confirmed our notion that plant available nitrogen at the study sites is low (approx. 1.12 kg/ha.) We propose that the nitrogen addition will decrease A. purpurea biomass and increase C3 biomass. We hypothesize this will occur as a result of A. purpurea’s competitive advantage being diminished as more nitrogen is made available to the plant community.
Technical Abstract: Purple threeawn (Aristida purpurea) is a native grass capable of rapidly increasing on rangelands, forming near monocultures, and arresting ecological succession. Productive rangelands throughout the Great Plains and Intermountain West have experienced increases in purple threeawn abundance, leading to reductions in overall forage quality as well as suitable wildlife habitat. Our objectives were to: 1) examine prescribed fire and nitrogen additions as successional stimulants on purple threeawn invaded landscapes, and 2) reveal vegetation management strategies appropriate for reducing purple threeawn. Season of fire (summer, fall) and different levels of nitrogen (0 kg N/ha, 46 kg N/ha, 80 kg N/ha) were factorially arranged and tested in a completely randomized design on a sandy ecological site in southeastern Montana. We assessed biomass, cover, and plant diversity in July 2010 and at peak biomass of the first growing season following treatment, July 2011. Summer and fall prescribed fire reduced purple threeawn biomass by 92% and 73%, respectively. Fire decreased annual grass biomass and total biomass across seasons of fire. Nitrogen did not affect purple threeawn biomass. Cool-season perennial grass biomass more than doubled with nitrogen additions, but was not affected by fire. Crested wheatgrass (Agropyron cristatum) replaced purple threeawn as the dominant perennial grass in the plant community. Fire reduced species richness. Additional time is required to determine how prescribed fire and nitrogen additions have affected succession in this plant community. Our preliminary results indicate prescribed fire, particularly during the summer, is an effective management strategy for reducing purple threeawn dominance.