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4.15.8 Revegetation Success Criteria <br />Colowyo will meet the requirements of this Subsection to insure that the post-mining <br />vegetation will be adequate for final bond release. As delineated under Subsections <br />4.15.7 and 2.05.4, Colowyo will utilize established reference areas (see Section 4.15.7 <br />above) for the purpose of comparing vegetation information between the reclaimed area <br />and the undisturbed area for the variables of ground cover and production. For the <br />variables of woody plant density and species diversity, Colowyo shall compare <br />revegetated area parameters against defined standards detailed later in this section. Data <br />to be used in these comparisons must be from statistically adequate sampling (where <br />necessary) as indicated in Rule 4.15.11. <br />Herbaceous Cover <br />For both Pre-2008 and Post-2008 revegetation targeting (and achieving) the rangeland <br />land use subcomponent of razingland, herbaceous cover of the revegetated area will be <br />considered adequate for final bond release if it is not less than 90% of the herbaceous <br />cover as determined from the reference areas with a 90% statistical confidence utilizing a <br />standard students statistical t-test comparison of the means. As allowed under the rules <br />promulgated on 9/14/05, these comparisons may utilize one of three methods detailed <br />under Rule 4.15.11 (2) [(a), (b) or (c)]. Also as allowed by Rule 4.15.7 (4), either <br />weighted-average or individual protocols will be followed depending on the resulting <br />community that evolves (see Section 4.15.7 above). For grassland testing the weighted <br />average approach (Rule 4.15.7 (4) (b)) will be utilized where reference area data and <br />revegetated area data are "weighted" (each combined into single values for comparison) <br />based on the proportional acreage of pre-mine communities within the disturbance area <br />footprint. Testing will then follow procedures detailed under Rule 4.15.11 (2) with <br />preference being given first to subsection (a) [direct comparison], second to subsection <br />(c) [reverse-null testing], and third subsection (b) [classic t-test]. <br />For Post-2008 sagebrush steppe revegetation (targeting the rangeland land use <br />subcomponent of wildlife habitat), herbaceous cover will be considered adequate for final <br />bond release if it is not less than 70%* of the sagebrush reference area's herbaceous cover <br />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. <br />• The value of 70% has been selected given the following rationale: 1) herbaceous competition must be <br />significantly restricted to facilitate emergence and growth of shrubs as indicated under Rule 4.15.11 (3) (ii); <br />2) the original value is 90%; 3) a value of 50% seems too low to adequately control erosion; 4) by regulation <br />(4.15.11 (3)(a)) a reduction to 70% is allowed for one of the demonstrations for revegetation success for <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 />4.15-15 Revision Date: 3/14/08 <br />Revision No.: TR-72