Effects of Mowing and Tebuthiuron on the Nutritional Quality of Wyoming Big Sagebrush

Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) is the most abundant and widely distributed subspecies of big sagebrush and has been treated through chemical application, mechanical treatments, and prescribed burning in efforts thought to improve habitat conditions for species such as greater sage-grouse (Centrocercus urophasianus) and mule deer (Odocoileus hemionus). Although the response of structural attributes of sagebrush communities to treatments is well understood, there is a need to identify how treatments influence the quality of sagebrush as winter food for wildlife. Our purpose was to identify how mowing and tebuthiuron treatments influenced dietary quality of Wyoming big sagebrush in central Wyoming. Two study areas were mowed in January and February 2014, and tebuthiuron was applied in two study areas in May 2014. We constructed 6 exclosures in each of these four study areas (24 total), which encompassed 30 × 30 m areas of treated and untreated sagebrush within each exclosure. Samples of current annual growth were collected from 18 sagebrush plants from treated and 12 plants from control portions of mowing exclosures during November 2013–2015 and tebuthiuron exclosures during November 2014–2015. Samples were analyzed for crude protein and plant secondary metabolites known to influence dietary selection of sagebrush by sage-grouse and other sagebrush-occurring herbivores. Our results suggest mowing and tebuthiuron treatments may slightly increase crude protein concentrations directly after treatments without immediate changes in plant secondary metabolites. Slight increases in dietary quality of sagebrush following treatments coupled with potential trade-offs with loss of biomass associated with treatments corroborates previous research that treating Wyoming big sagebrush may have little benefit for sage-grouse and other sagebrush-dependent wildlife. Future work should evaluate not only how treatments influence sage-grouse habitat use and reproductive success but also how treatments influence other wildlife species in fragile sagebrush ecosystems.