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United States Department of Agriculture

Agricultural Research Service

Research Project: Adaptive Rangeland Management of Livestock Grazing, Disturbance, and Climatic Variation

Location: Livestock and Range Research Laboratory (LARRL)

Title: Fire effects on basal area, tiller production, and mortality of the C4 Bunchgrass, Purple Threeawn

Authors
item STRONG, DUSTIN
item Ganguli, Amy -
item VERMEIRE, LANCE

Submitted to: Fire Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2013
Publication Date: September 1, 2013
Repository URL: http://handle.nal.usda.gov/10113/59345
Citation: Strong, D.J., Ganguli, A.C., Vermeire, L.T. 2013. Fire effects on basal area, tiller production, and mortality of the C4 Bunchgrass, Purple Threeawn. Fire Ecology. 9(3):89-99.

Interpretive Summary: Purple threeawn (Aristida purpurea Nutt.) 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) quantify fire effects on purple threeawn plant characteristics and 2) determine the relationship between purple threeawn survival and fire behavior. Heat duration and dosage were good predictors of purple threeawn mortality. Summer prescribed fire appears to be the best management tool to reduce purple threeawn abundance.

Technical Abstract: Fire behavior associated with wild and prescribed fires is variable, but plays a vital role in how a plant responds to fire. The relationship of fire behavior to rangeland plant community response has not been investigated, with a few exceptions, until recently. Fire is an important ecological process in many rangeland ecosystems and can be used as a tool to maintain grassland plant communities and/or shift community composition. Purple threeawn (Aristida purpurea Nutt.) is a grass native to North America with poor forage quality and the ability to form near monocultures. Therefore, the identification of tools to reduce Aristida abundance is desirable. We assessed the effects of summer and fall prescribed fire on purple threeawn plant basal area, tiller production, and plant survival one growing season post-fire in the northern Great Plains. Thermocouples and portable data loggers were used to measure the maximum temperature, heat duration, and heat dosage individual purple threeawn plants experienced. Fire reduced basal area (P < 0.001) and tiller production (P < 0.001). Heat dosage (C-statistic = 0.69) and heat duration (C-statistic = 0.65) were good predictors of purple threeawn mortality. A restrospective analysis showed maximum temperatures were similar for fall and summer fires but heat duration and dosage was greater for summer fires (P < 0.03). Our results indicate purple threeawn is a fire sensitive species. The ability to predict purple threeawn mortality could enhance the efficacy of prescribed fire as tool to rehabilitate purple threeawn and other Aristida-dominated plant communities.

Last Modified: 9/29/2014
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