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"....vegetation capable of hiding 90 percent of a standing adult <br />• deer or elk from view of a human at a distance equal to or less <br />than 61 meters (200 ft.)." <br />The above definition is for coniferous tisber stands of various aEes in the <br />Blue Mountains of Oregon and *dashington. At Trapper Pfiae, 90 percent conceal- <br />ment in mountain shrub vegetation almost always occurs in much less than 200 <br />feet. A conacrvative guess for a typical ma.tur.e mountain scrub type would be <br />that 9U percent screening occurs in 50 feet or less. <br />Thomas, et al (1979) stated that: <br />"Topography has not been demonstrated to be a substitute for <br />vegetative cover. Topography can have a marked impact, however, <br />on the value of a particular type of vegetation for hiding <br />cover." (emphasis ours) <br />• In order to calculate the minimum clump size foc optimum hiding cover, the dis- <br />tance for 90 percent concealment must be known. Figure 3 from Thomas et al., <br />(1979) shows a method for determining minimum clump size_ In their example, <br />the minimum distance for 90 percent concealment is 200 fee[ (one sight dis- <br />tance). An animal must penetrate either zone 1 or 4 the full distance (200 <br />ft.) before it will be 90 percent hidden. In zone 5 (200 feet in diameter), or <br />zones 2 and 3 (a total o: 800 feet in diameter) an animal a.~11 be free to move <br />about unseen. Therefore, the minimum average diameter of: :a shrub clump for <br />optimum hiding cover in this example is 600 feet (200 feet, or one sight dis- <br />tance + 200 feet hiding cover + 200 feet, or one sight distance 600 feet). For <br />Trapper Mine, the minimum clump size using a sight distance of 50 feet is 300 <br />feet in diameter or 2 times the sight distance plus 200 feet hiding cover. <br />This arrangement results in a center area approximately 20•'0 feet in diameter <br />where animals are hidden. <br />The other type of cover important to wildlife is thermal comEr.. Thomas et al. <br />(1979) defines thermal cover as: <br />• "Cover used by deer or elk to assist in maintaininb honxoiothermy...." <br />-9- <br />