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4 4 1 3 Shrub Density Standards <br /> Revegetation standards for shrub reestablishment at Trapper Mine should not be established from direct <br /> comparisons to reference areas or premining shrub densities. An analysis of stem density data in <br /> Section 2.3.3.3 shows that the naturally occurring density of shrubby stems is prohibitive to use by <br /> grazing ungulates. <br /> In general terms, Young et al., (1967) found that forest density and understory vegetation influenced the <br /> distribution of forage utilization in areas of study in northern Oregon. Clary et al. (1978) identified two <br /> variables, perennial grass production and ponderosa pine stem density, as being primarily responsible for <br /> the variation in the pounds of forage consumed by cattle. Cook (1966) investigated twenty-one separate <br /> variables for the effect on utilization by cattle. He identified eleven variables as having a significant <br /> effect on utilization with the density of brush being consistently in the top eight. Kufeld (1977) in his <br /> study of oak stands found that dense stands will prevent access by cattle and elk and that production of <br /> grasses and forts occurring under such stands may be suppressed. Investigations have shown that <br /> cattle prefer to forage in open areas and will avoid areas where an overstory exists (Reynolds 1962; <br /> McEwen and Dietz, 1965; George and Powell, 1979). <br /> Boyd (1970) conducted an extensive study of elk of the White River Plateau. Included in his study were <br /> the degree of utilization by elk of various densities of Gambel's oak. He concluded that elk use is <br /> inhibited at densities of thiryfive percent and that elk are physically excluded on densities exceeding fifty- <br /> one percent. Boyd also indicated that mature and aged stands generally have densities that exceed the <br /> above value. In addition, overmature plants are of such height as to be out of reach to deer and elk, <br /> even during winter months. <br /> Density measurements by Boyd are essentially an indication of aerial cover. Section 2.3.1 discusses <br /> cover measurements at Trapper Mine in relation to habitat descriptions. Tables 2.3-2 and 2.3-4 illustrate <br /> in percent relative cover, shrub cover by species and cover by lifeform for the mountain shrub vegetative <br /> types. <br /> Jefferies (1965) conducted a study on Gambel's oak at the San Juan Basin Experiment Station. <br /> Jefferies major conclusion was that by thinning oak brush stands, greater forage production could be <br /> realized on oak dominated ranges. It was Jefferies opinion that lower production under oak was due to <br /> the predominance of cool season species and the high degree of shading from the oak canopy. This is <br /> corroborated by the work of Tiedeman and Schmutz (1966) who were able to increase grass production <br /> by 770 Ibs per acre by destroying an oak canopy. Kufeld (1977) found that grasses increased in <br /> abundance by forty-four percent after treating oak brush. Two years after a spraying treatment, he found <br /> that elk use had increased by seventy-three percent and deer use was up sixteen percent. While deer <br /> use seems less inhibited by high shrub density, Boyd (1970) found that when oak densities (of canopy <br /> cover) above fifty-one percent were thinned, it did not adversely affect wintering deer herds. <br /> 4-112 <br /> Revision: <br /> Approved: ��g� <br />