Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Wildland Resources


Eric T. Thacker


Parker Mountain, is located in south central Utah, it consists of 153 780 ha of high elevation rangelands dominated by black sagebrush (Artemisia nova A. Nelson), and mountain big sagebrush (Artemisia tridentata Nutt. subsp. vaseyana [Rybd.] Beetle) communities. Sagebrush obligate species including greater sage-grouse (Centrocercus urophasianus) depend on these vegetation communities throughout the year. Parker Mountain is owned and managed by Utah School and Institutional Trust Lands Administration, Bureau of Land Management, and the United States Forest Service. Land management on Parker Mountain include wildlife conservation and providing sustainable ecosystem services such as livestock grazing.

My research described the species composition of the black sagebrush communities, evaluated the long-term vegetation responses to two mechanical (Dixie harrow/Lawson aerator) and one chemical treatment (tebuthiuron), and herbaceous biomass responses to tebuthiuron treatments in mountain big sagebrush communities on Parker Mountain.

My results indicated when black sagebrush canopy cover was <20%, average grass canopy cover was highest (13%). When black sagebrush canopy cover exceeded 40%, grass canopy cover was lowest (8%). Forb canopy cover was relatively consistent (5%) across black sagebrush communities with >20% canopy cover. Communities with <20% black sagebrush canopy cover had the lowest forb canopy cover.

Tebuthiuron reduced mountain big sagebrush percent canopy cover (>9 years), increased grass canopy cover, and increased forb canopy cover more than the two mechanical brush control methods. Tebuthiuron treatments shifted sites from xeric to more mesic plant communities, which resulted in increased percent forb cover required by greater sage-grouse during late-brooding.

Herbaceous biomass increased under tebuthiuron treatments in mountain big sagebrush pastures. Tebuthiuron treatments also reduced live sagebrush canopy cover for at least 9 years.