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2.3 Section 16 <br />2.3.1 S16 Year 12 <br />S16Y12 is comprised of 2 units in Section 16 <br />(S16009 and S16010) that make up 19.8 acres of gently <br />sloping revegetation that has a predominately <br />southeasterly aspect. This unit was seeded in 1996 and <br />therefore, has undergone twelve growing seasons prior <br />to sampling in 2008. A total of 39 plant taxa were <br />observed in the unit (see Table AB-1). Current annual <br />production across the unit averaged 2,253.6 pounds per <br />acre in 2008 with perennial grasses and perennial (orbs <br />the dominant categories (see Compendium 3). Ground <br />cover in S16Y12 consisted of 72.2% live vegetation, <br />0.2% rock, 23.9% litter, and bare soil exposure of <br />3.7%. Perennial cover across the unit averaged 70.9% <br />with annual and biennial cover averaging 2.8%. <br />Dominant taxa were thickspike wheatgrass, cicer <br />milkvetch, streambank wheatgrass (Agropyron <br />riparium), western wheatgrass, and basin wildrye <br />(Eiymus cinereus), with 31.1%, 10.0%, 8.4%, 4.0%, <br />and 3.1% average cover, respectively. Woody plant <br />density was determined from 20 belt transects. Density <br />(Table 2) totaled 117 young and mature stems per acre <br />with big sagebrush (Artemisia tridentata) the dominant <br />woody plant. With regard to diversity, S16Y12 <br />exhibited 6 perennial grasses and 1 perennial forb with between 3% and 50% relative cover. <br />Unit S16Y12 currently passes the bond release diversity standard of 3 perennial grasses and 1 <br />perennial forb with between 3% and 50% relative cover (see Chart 6). This unit easily passes both the <br />cover and production bond release comparisons to the reference areas (see Charts 3 and 4). However, <br />this unit does not presently meet the woody plant density standard of 90% of 1000 stems per acre and <br />will probably not meet this in the foreseeable future due to the heavy competitive grass cover. See <br />Appendix AA - Section 7.3 for a discussion on options and recommendations with regard to woody plant <br />density. An occasional noxious weed (Canada thistle and Queen Anne's lace) were observed in this unit. <br />Annual bromes are not present in patches or populations, therefore, annual cover is quite low. <br />At present, S16Y12 is a good example of an improved pasture grassland community that would <br />contribute to the local system with respect to both cover and foraging habitat for wildlife (especially elk), <br />as well as provide a variety of management opportunities for livestock grazing. <br />Rio Tinto Energy America/Colowyo Mine Page 16 Revegetation Monitoring - 2008