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RULE 4 PERFORMANCE STANDARDS <br />For "targeted" Post -2008 sagebrush steppe revegetation (targeting the rangeland land use <br />subcomponent of wildlife habitat), herbaceous cover will be considered adequate for final bond <br />release if it is not less than 70%* of the sagebrush reference area's herbaceous cover with a 90% <br />statistical confidence utilizing a standard students statistical t-test comparison of the means. If <br />necessary, a reverse -null hypothesis testing procedure may be utilized in accordance with <br />procedures detailed in Rule 4.15.11 (2) (c). As allowed under Rule 4.15.8 (3) (ii), relaxation of <br />the herbaceous cover standard for areas targeting wildlife habitat post -mining land uses is designed <br />to compensate for revegetation techniques (prescribed ecological reclamation approach) that must <br />discourage grasses to encourage shrubs in the post-revegetated community. For "evolved" post - <br />2008 sagebrush steppe revegetation, the grazingland cover standard will be maintained. <br />A higher percentage of herbaceous cover is not practical or desirable for the following reasons: <br />1. It is well documented that in mined -land reclamation the establishment of shrubs to reach <br />bond release levels has proven to be very difficult. Perhaps the most detrimental condition <br />affecting shrub establishment is the competition from herbaceous vegetation. At a <br />minimum herbaceous cover levels should be less than the premining condition. If the <br />herbaceous levels to be obtained were set higher than the premining condition, the ability <br />to achieve bond release levels for shrubs would be most adversely affected. Higher levels <br />of herbaceous cover would adversely compete against woody vegetation and hinder its <br />successful establishment. <br />2. In mined -land reclamation it is important to have adequate herbaceous cover to provide for <br />erosion control. The reference areas at Colowyo indicate herbaceous cover values of 41.8% <br />and 30.17% for the mountain shrub and sage reference areas, respectively. <br />Colowyo is located at approximately- 7,300 feet in elevation. The period of highest <br />potential erosion occurs in the springtime during snowmelt. At this time of year, erosion <br />control is provided almost exclusively by herbaceous vegetation. Erosion control by shrub <br />cover is virtually insignificant since the potential erosion occurs from snowmelt rather than <br />raindrop impact. Therefore, if pre -mining levels of herbaceous vegetative cover can be re- <br />established, logically a comparable level of erosion control will be achieved. <br />3. The ability to achieve adequate levels of herbaceous cover at Colowyo is, without question, <br />quite possible. The vegetative monitoring completed at Colowyo during the last three <br />decades, and summarized in annual reports, indicates that the premining levels of <br />herbaceous cover are easily achieved. <br />In fact, the vegetative data as summarized in the annual reports indicate that the levels of <br />herbaceous cover on the reclaimed areas may have exceeded the premine condition by 30% <br />to 50%. <br />The value of 70% has been selected given the following rationale: 1) herbaceous competition must be significantly restricted to facilitate emergence <br />and growth of shrubs as indicated under Rule 4.15.11 (3) (ii); 2) the original value is 90%; 3) a value of 50% seems too low to adequately control <br />erosion; 4) by regulation (4.15.11 (3)(a)) a reduction to 70% is allowed for one of the demonstrations for revegetation success for woody plant <br />density; and 5) 70% of the herbaceous material in a native reference area should be adequate to control erosion on slopes 10% or less. <br />Rule 4 Performance Standards 4-65 Revision Date: 5/25/18 <br />Revision No.: RN -07 <br />