Date of Award:

8-2012

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Advisor/Chair:

Terry Messmer

Abstract

The Utah prairie dog (Cynomys parvidens) was listed by the U.S. Fish and Wildlife Service as an endangered species in 1973 because of range-wide population declines. The species was reclassified as threatened in 1984 because of population increases on private lands. Habitat fragmentation coupled with a lack of suitable habitat has impeded species recovery. Desired species habitat conditions include 0-8% shrub cover, 12-40% cool-season grass cover, and 1-10% perennial forb cover. Cool-season grasses are critical for Utah prairie dogs because of high spring energy requirements. Past research suggested that reducing shrub cover may increase cover of desired grasses and forbs. From 2008-2010, I evaluated the effects of high intensity fall sheep grazing and low application of herbicide (tebuthiuron) as tools to reduce shrub cover and enhance grass and forb cover on the Awapa Plateau Utah prairie dog recovery area in south-central Utah. I placed 1700 ewes in 4 ha stratified and randomly selected plots until >70% vegetation utilization was achieved. Five additional randomly-selected plots were treated with tebuthiuron at a rate of ~1.68 kg/ha. Percent cover of grass, forbs, and shrubs was recorded on treatments and paired control plots in June 2009 and 2010 to determine treatment vegetation responses. I also affixed 22 juvenile Utah prairie dogs with radio transmitters to determine if over-winter survival differed relative to treatment. Live shrub cover was lower on grazed plots in year 1 (P<0.001) and in year 2 (P=0.015). Dead shrub cover in grazed plots was higher in year 1 (P<0.001). Grazed plots exhibited increased forb cover from year 1 (P=0.104) to year 2 (P=0.008). Live shrub cover was lower in herbicide plots in year 2 (P=0.002). Dead shrub cover in herbicide plots was higher in year 2 (P=0.006). Tebuthiuron and grazed plots exhibited a reduction in shrub height (P=0.010, P=0.026, respectively). Tebuthiron plots exhibited less grass cover (P=0.034). Intensive sheep grazing and a low application of tebuthiuron reduced both shrub cover and vertical structure, but failed to increase the percent of grass cover when compared to the control plots. All plots exhibited reduced grass cover in 2010 in response to below normal precipitation. However, percent grass cover was higher on the grazed plots. It is possible that low inherent site productivity in combination with below normal average precipitation compromised treatment effects. Because of radio transmitter failure, I was not able to obtain survival data after hibernation. Prairie dog counts and weights did not differ by treatment type. If climate change reduces overall precipitation on the Awapa Plateau, recovery of the Utah prairie dog on this site will be problematic.

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This work made publicly available electronically on July 30, 2012.

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