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2.3.2 S16 Years 13, 14, & 15 <br />51bY1.i,14,&15 Is comprised of 5 units in Section <br />16 (S16002, S16003, 516005, 516006, and S16008) <br />that make up 163.7 acres of gently sloping revegetation <br />that has predominately a southeasterly aspect. This <br />unit was seeded from 1993-1995 and therefore, has <br />undergone thirteen to fifteen growing seasons prior to •-?? <br />sampling in 2008. A total of 34 plant taxa were <br />observed in the unit (see Table AB-1). Current annual , • • • <br />production across the unit averaged 2,099.8 pounds <br />per acre in 2008 with perennial grasses the dominant . • <br />category (see Compendium 4). Ground cover in <br />S16Y13,14,&15 consisted of 60.7% live vegetation, • • • • <br />0.2% rock, 33.0% litter, and bare soil exposure of <br />6.2%. Perennial cover across the unit averaged 57.6% • • <br />with annual and biennial cover averaging 3.1%. <br />Dominant taxa were thickspike wheatgrass, western • • • <br />wheatgrass, crested wheatgrass (Agropyron cr&tatum), <br />basin wildrye, and cicer milkvetch, with 19.7%, 15.9%, <br />4.9%, 3.8%, and 3.2% average cover, respectively. <br />Woody plant density was determined from 20 belt <br />transects. Density (Table 2) totaled 194 young and <br />Rw^ <br />mature stems per acre with big sagebrush the'°m16-o'°•r <br />dominant woody plant. With regard to diversity, <br />S16Y13,14,&15 exhibited 6 perennial grasses and 1 perennial forb with between 3% and 50% relative <br />cover. <br />Unit S16Y13,14,&15 currently passes the bond release diversity standard of 3 perennial grasses and <br />1 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). This unit <br />does not presently meet the woody plant density standard of 90% of 1000 stems per acre and will <br />probably not meet this in the foreseeable future due to the heavy competitive grass cover. See Appendix <br />AA - Section 7.3 for a discussion on options and recommendations with regard to woody plant density. <br />An occasional noxious weed (Canada thistle) was observed in this unit. Annual bromes are not present in <br />patches or populations, therefore, annual cover is quite low. <br />At present, S16Y13,14,&15 is a good example of an improved pasture grassland community that <br />would contribute to the local system with respect to both cover and foraging habitat for wildlife <br />(especially elk), as well as provide a variety of management opportunities for livestock grazing. <br />Rio Tinto Energy America/Colowyo Mine Page 18 Revegetation Monitoring - 2008