Date of Award:

5-2004

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

Neil E. West

Committee

Neil E. West

Committee

Fred Provenza

Committee

Kenneth C. Olson

Abstract

Traditional chemical and mechanical treatments of Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis) are costly and have typically focused solely on increasing forage for livestock production. Managing these systems biologically with grazing can potentially reduce costs and increase both biodiversity and understory production as well as rejuvenate Wyoming Big Sagebrush (ARTRWY). This experiment was conducted on Deseret Land and Livestock Ranch in northern Utah in October 2003. One hundred and twenty sheep (dry ewes) grazed 3, 60m x 40m plots (40 sheep plot-1). Sheep were provided a protein-energy supplement to facilitate use of the secondary metabolites found in ARTRWY forage. I used the reference unit method to estimate (g x m-2) phytomass in the following plant categories immediately before, immediately after, and one year following grazing: total phytomass, current annual growth (CAG) of ARTRWY, the woody portion of ARTRWY, CAG of other shrubs, the woody portion of other shrubs, grasses, forbs, litter (woody and herbaceous), and standing dead (woody and herbaceous). I also measured plant species richness and abundance, as well as estimates of the age class structure of sagebrush. Sheep used 98% of the total available forage. One year following grazing, total phytomass decreased by 43% relative to pregraze levels, due primarily to the reduction in biomass of ARTRWY. The CAG of ARTRWY decreased by 66%, while grasses increased by 43%, forbs increased 60%, and the number of species encountered in the grazed plots increased 42%. While caution should be exercised, considering the short time frame of my study, fall grazing by sheep supplemented with nutrients may be a useful way to enhance shrub age class structure and increase herbaceous species richness, dominance, and production in sagebrush steppe.

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