Date of Award:

5-2012

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

Frederick D. Provenza

Committee

Frederick D. Provenza

Committee

Roger E. Banner

Committee

Juan J. Villalba

Committee

Randall D. Wiedmeier

Abstract

Historic and repetitious spring grazing by livestock, combined with altered fire regimes, has increased the density and abundance of big sagebrush and reduced the frequency of perennial grasses and forbs on many western landscapes. Periodic disturbance is critical for maintaining and improving sagebrush ecosystems. Compared with traditional disturbances – chemical, mechanical, and fire – strategic grazing with livestock offers several benefits. They include creating locally adapted cattle that can rejuvenate sagebrush steppe, which reduces costs associated with mechanical and chemical rejuvenation treatments and feeding cattle during winter, the major cost of ranch operation.

I evaluated the practicality of strategically timed (fall) grazing with cattle at high stock densities on land dominated by sagebrush. From 2007 to 2009, I monitored cattle use of sagebrush, cattle performance (body weights), and the ensuing response of grasses, forbs, and sagebrush.

Cow/calf pairs – provided with protein and energy supplements to offset the effects of terpenes in big sagebrush – selected big sagebrush as a significant portion of their diet. Cattle learned to eat sagebrush and the effects occurred in fetuses in utero, in calves early in life, and in adults later in life. Cattle of all ages with experience of sagebrush lost less weight, or actually gained more weight, than cattle naïve to sagebrush. Fall grazing by cattle reduced the abundance of big sagebrush and promoted production of grasses and forbs. Fall and winter are ideal times for grazing to induce such changes in plant community structure because perennial herbs are largely dormant.

My research suggests grazing by cattle can be a biologically and economically effective way to accomplish habitat renovation. Rather than attempting to convert sagebrush steppe landscapes to grass at extravagant costs, as we have done historically, we must now consider how to create locally adapted herds of livestock and complementary management practices that ensure long-term health of sagebrush ecosystems. As many ranchers already feed hay to cows during winter, using sagebrush steppe vegetation as an additional forage resource would allow ranchers to feed roughly half the hay, which would greatly reduce winter feed costs. In addition to financial savings in hay, the secondary benefits from improving sagebrush steppe condition and productivity would result in habitat improvements for both livestock and wildlife.

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This work made publicly available electronically on May 10, 2012.

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