Date of Award:

5-1-2007

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Life Sciences: Biology

Committee Chair(s)

Kimberly A. Sullivan

Committee

Kimberly A. Sullivan

Committee

Thomas C. Edwards

Committee

Morgan Ernest

Abstract

Shrub-dominated ecosystems on private lands are important rangeland resources through much of the western U.S., including Rich County, Utah. Because of its important role in livestock production, this shrubsteppe ecosystem has been exposed to a variety of sagebrush removal methods. Little is known about the relative effects of chemical, mechanical, or burn treatments on breeding passerine communities. Furthermore, most studies address only short-term effects. We studied breeding passerine communities and vegetation on 17 untreated sites and 49 range sites treated between 1962 and 2004 to examine the effects of treatment type and treatment age. The sagebrush treatments produced considerable changes in habitat composition. Shrub cover was lower on fire and mechanical treatments compared to chemically treated and untreated sites (p < 0.0001). Mechanical treatment resulted in more bare ground when compared to the other treatment types (p < 0.0001). Over time, grass and forb cover decreased, while shrub cover increased. After 20 years, treatment sites resembled untreated sites in shrub cover. Response by the bird populations to these habitat changes varied among species. Brewer's Sparrows, Sage Thrashers, and Green-tailed Towhees preferred shrubby habitats. These 3 bird species reached their highest densities at chemically treated and control sites (all p < 0.05). Brewer's Sparrow densities were higher at control sites and sites treated in the 1980s and 90s than more recently treated sites (p < 0.01). On the other hand, Vesper Sparrows and Horned Larks were detected more frequently in open, grassy sites. Horned Lark densities were higher in mechanically treated sites than on chemically treated sites, sites treated by fire, and untreated sites (p < 0.0007). Given the differential responses of breeding passerines to rangeland alteration, managing a site for shrubsteppe wildlife is difficult as practices that benefit some species are detrimental to others. Thus, range managers should plan for a dynamic pattern of different aged stands of sagebrush across a landscape. The decision to remove sagebrush, the removal method, and timing of treatment require careful consideration of one's management goals, vegetation types, site potential, costs, and opportunities.

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