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with a 90% statistical confidence utilizing a standard students statistical t-test comparison <br />of the means. If necessary, a reverse-null hypothesis testing procedure may be utilized in <br />accordance with procedures detailed in Rule 4.15.11 (2) (c). As allowed under Rule <br />4.15.8 (3) (ii), relaxation of the herbaceous cover standard for areas targeting wildlife <br />habitat post-mining land uses is designed to compensate for revegetation techniques <br />(prescribed ecological reclamation approach) that must discourage grasses to encourage <br />shrubs in the post-revegetated community. For "evolved" post-2008 sagebrush steppe <br />revegetation, the grazingland cover standard will be maintained. <br />A higher percentage of herbaceous cover is not practical or desirable for the following <br />reasons: <br />1. It is well documented that in mined-land reclamation the establishment of shrubs <br />to reach bond release levels has proven to be very difficult. Perhaps the most <br />detrimental condition affecting shrub establishment is the competition from <br />herbaceous vegetation. At a minimum herbaceous cover levels should be less <br />than the premining condition. If the herbaceous levels to be obtained were set <br />higher than the premining condition, the ability to achieve bond release levels for <br />shrubs would be most adversely affected. Higher levels of herbaceous cover <br />would adversely compete against woody vegetation and hinder its successful <br />establishment. <br />2. In mined-land reclamation it is important to have adequate herbaceous cover to <br />provide for erosion control. The reference areas at Colowyo indicate herbaceous <br />cover values of 41.8% and 30.17% for the mountain shrub and sage reference <br />areas, respectively. <br />Colowyo is located at approximately- 7,300 feet in elevation. The period of <br />highest potential erosion occurs in the springtime during snowmelt. At this time <br />of year, erosion control is provided almost exclusively by herbaceous vegetation. <br />Erosion control by shrub cover is virtually insignificant since the potential erosion <br />occurs from snowmelt rather than raindrop impact. Therefore, if pre-mining levels <br />of herbaceous vegetative cover can be re-established, logically a comparable level <br />of erosion control will be achieved. <br />3. The ability to achieve adequate levels of herbaceous cover at Colowyo is, without <br />question, quite possible. The vegetative monitoring completed at Colowyo during <br />the last three decades, and summarized in Annual Reports, indicates that the <br />premining levels of herbaceous cover are easily achieved. <br />In fact, the vegetative data as summarized in the Various Annual Reports indicate <br />that the levels of herbaceous cover on the reclaimed areas may have exceeded the <br />premine condition by 30% to 50%. <br />woody plant density; and 5) 70% of the herbaceous material in a native reference area should be adequate to <br />control erosion on slopes 10% or less. <br />4.15-18 Revision Date: 12/22/09 <br />Revision No.: TR-84