Sheep grazing in Douglas-fir plantations of Oregon's Coast Range and its impact on big game habitat Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/1v53k162t

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  • As part of investigations to evaluate the suitability of sheep grazing in Douglas-fir (Pseudotsuga menziesii) plantations of Oregon's Coast Range, this research was designed to evaluate the effectiveness of sheep grazing in suppressing unwanted vegetation, determine seasonal variations in forage quality, and investigate the impact of sheep grazing on big game habitat. Estimates of forage quantity and quality present in October and March from grazed vs. ungrazed portions of 5 study plantations were used to evaluate effects of grazing. In addition, 15 forage species were collected seasonally and analyzed for percent crude protein, in vitro dry matter digestibility (IVDMD), acid detergent fiber (ADF), cell wall contents (CWC), and mineral content. In general, utilization of brush by sheep was moderate to heavy, except in the spring of 1982, when brush was utilized relatively lightly. Sheep grazing effectively reduced both total and brush net growth present in October (p < .01). The effect of grazing on both total and brush net growth varied in magnitude between plantations. The potential for sheep to suppress individual brush species is discussed. Forages collected seasonally during the grazing season appeared to be generally adequate in crude protein for nutrient requirements of wild ungulates and domestic sheep. Browse had relatively low IVDMD values throughout the growing season. Forbs and graminoids exhibited high IVDMD in early spring and spring, and relatively low IVDMD values in summer and fall. Averaged over seasons, browse was lower in ADF and CWC (p < .01) than graminoids and forbs. The relatively low IVDMD of all forage types in summer and fall suggests that forage may be limiting in digestible energy at those times of the year. Forages appeared to have adequate levels of minerals, except for selenium, which was deficient in all 4 species examined. Sheep grazing reduced total net growth, and net growth of browse and forbs (p < .01) in October. Net growth of graminoids was not affected by grazing. Forage from grazed areas generally had higher crude protein levels and tended to be more digestible than forage from ungrazed areas. Few differences in either crude protein or digestibility of forage from grazed vs. ungrazed areas were evident in the spring. However, a greater quantity (p < .01) of new, succulent forage was generally present in grazed areas compared to ungrazed areas. These data suggest that sheep grazing can affect big game forage supply in Oregon's Coast Range by improving forage quality in the fall and by increasing the quantity of high quality forage in the spring.
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