2010-06-28_REVISION - C1981019 (6)

Home Browse Search

cover across the unit averaged 72.6% (97.3% relative cover) with annual and biennial cover averaging 2.0% (2.7 relative cover). Dominant taxa were thickspike wheatgrass, cicer milkvetch, western wheatgrass (Agropyron smithii), and crested wheatgrass, with 20.2 %, 14.2 %, 9.4 %, and 9.2% average cover, respectively. With regard to diversity, the Phase III Bond Release Area exhibited 5 perennial grasses with between 3% and 50% relative cover (Table 2). Total relative cover for all forbs excluding noxious weeds in the Phase III area was 26.2 %. Table 5 displays the results from 9 shrub patches (with densities greater than 150 stems per acre) that occupy 11.45 acres of the 203.1 acres of Phase III revegetation (5.64%). The 9 shrub patches exhibited an average of 1,284 woody plants per acre. Table 7 exhibits the results from 45 belt transects collected at each sample site for woody plant density. Perusal of the table reveals that there is an average of 34.2 woody plants per acre in the Phase III bond release area (largely grassland areas). Current annual herbaceous production across the Phase III area averaged 1996.5 pounds per acre in 2009 with perennial grasses the dominant category (Table 3). 3.2 Reference Areas 3.2.1 Mountain Shrub Reference Area The Mountain Shrub Reference Area is comprised of approximately 18 acres of gently to moderately sloping vegetation that has a predominately northwesterly aspect (mesic) and easterly aspect ( xeric). Plates 5 and 6 show site conditions for 2008 and 2009, respectively. The Mountain Shrub Reference Area was expanded in 2005 to include the east - facing slope of the ridge to provide representation from the xeric subtype of the Mountain Shrub community. The purpose of this inclusion is to provide a better representation of the distribution of Mountain Shrub communities located on and around Colowyo properties. The xeric exposure tends to exhibit more elevated herbaceous parameters given a modest reduction in the overstory. This reference area is located on the undisturbed ridge immediately west of the West Pit Area (Maps 3 and 4). Current annual herbaceous production across the area averaged 584.6 pounds per acre in 2008 with perennial grasses the dominant category (Table 3). Ground cover in the Mountain Shrub Reference Area (Table 1 and Chart 1) consisted of 63.0% live vegetation, 0.5% rock, 31.3% litter, and bare soil exposure of 5.2 %. Perennial cover across the unit averaged 55.1% with annual and biennial cover averaging 7.8% and noxious weed cover with 0.1 %. Dominant taxa were big sagebrush (Artemisia tridentata), mountain snowberry (Symphoricarpos oreophi /us), cheatgrass, bluegrass (Poa agasizensis), and CEDAR CREEK ASSOCIATES, Inc. Page 16 Rio Tinto Energy America - Colowyo Mine 2009 Phase III Bond Release Evaluation — Year 2