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United States Department of Agriculture

Agricultural Research Service

Title: Invasion of Broom Snakeweed (Gutierrezia sarothrae) Following Disturbance: Evaluating Change in a State-and-Transition Model

Authors
item Thacker, Eric - UTAH STATE UNIVERSITY
item Ralphs, Michael
item Call, Christopher - UTAH STATE UNIVERSITY
item Benson, Brock - USDA-NRCS
item Green, Shane - USDA-NRCS

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 21, 2008
Publication Date: May 3, 2008
Repository URL: http://USDA.ars.pprl
Citation: Thacker, E., Ralphs, M.H., Call, C., Benson, B., Green, S. 2008. Invasion of Broom Snakeweed (Gutierrezia sarothrae) Following Disturbance: Evaluating Change in a State-and-Transition Model. Rangeland Ecology and Management, Vol. 61, Issue 3, pp. 263-268. DOI:10:2111/07.043.1

Interpretive Summary: Broom snakeweed is an aggressive native invasive species which can thrive after disturbance in semi-arid areas of the western U.S. The objectives of this study were to evaluate the ability of four plant community phases within the sagebrush shrub-steppe community to resist snakeweed invasion. A fence line contrast created two plant community phases; phase 1 received alternate-year, fall cattle grazing, and was dominated by bluebunch wheatgrass and an open stand of Wyoming big sagebrush; phase 3 received continuous, annual, spring cattle grazing and was dominated a dense stand of sagebrush with an understory of Sandberg bluegrass. Portions of phases 1 and 3 were burned in a 2001 wildfire, removing the sagebrush. Phase 2 was dominated by bluebunch wheatgrass, and phase 4 was dominated by Sandberg bluegrass. Over the 5 year period, snakeweed cover in phase 1 declined from 3% to 0%, due to suppression from the bunchgrasses and sagebrush; in phase 2, snakeweed was removed by the fire and there was no reinvasion; snakeweed cover in the sagebrush dominated phase 3 remained unchanged at 4%; snakeweed cover in phase 4 steadily increased from 2% to 31%, thus replacing sagebrush dominance in this community. The results suggest that plant communities dominated by bluebunch wheatgrass or big sagebrush will resist snakeweed invasion and expansion on this sagebrush-steppe site. A state and transition model was created for managing snakeweed in this sagebrush-steppe community.

Technical Abstract: Broom snakeweed (Gutierrezia sarothrae) is a very aggressive native invasive species which can thrive after disturbance in semi-arid areas of the western U.S. The objectives of this study were to evaluate the ability of four plant community phases within the same sagebrush shrub-steppe community to resist snakeweed invasion over a 5-year period (2002-2006), and to develop a state-and-transition model for range managers to use as a tool to minimize snakeweed invasion. The study site originally had two plant community phases: phase 1 received alternate-year, fall cattle grazing, and was dominated by bluebunch wheatgrass (Elymus spicatus) and an open stand of Wyoming big sagebrush (Artemisia tridentate ssp. wyomingensis); phase 3 received continuous, annual spring cattle grazing and was dominated a dense stand of Wyoming big sagebrush with an understory of Sandberg bluegrass (Poa secunda). Portions of phases 1 and 3 were burned in a 2001 wildfire, removing the Wyoming big sagebrush, and creating phases 2 and 4. Phase 2 was dominated by bluebunch wheatgrass, and phase 4 was dominated by Sandberg bluegrass. Four 10 m transects were placed within each phase. Densities of shrubs and snakeweed were counted in 1 m x 10 m belt transects and foliar cover was estimated by the line intercept method. Over the 5 year period, snakeweed cover in phase 1 was reduced from 3.1% to 0%, due to suppression from the bunchgrasses and sagebrush; snakeweed in phase 2 was removed by the fire, and there was no reinvasion; snakeweed cover in phase 3 remained unchanged at 4.1%; snakeweed cover in phase 4 steadily increased from 2.3% to 31%. Snakeweed age class densities in phase 4 showed the progression of snakeweed invasion. The stand progressed from 26.6 seedlings/m2to 12.0 mature plants/m2. The above ground biomass production showed that Phase 4 had the highest snakeweed biomass (833 kg/ha) and phases 1 and 2 had the highest total above ground biomass (2430 kg/ha). The results suggest that bluebunch wheatgrass or big sagebrush will resist snakeweed invasion and expansion on a sagebrush-steppe site. A state and transition model was created for managing snakeweed in this sagebrush-steppe com

Last Modified: 4/17/2014
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