2008-03-13_REPORT - C1981019 (2)

Home Browse Search

2.2 East Pit 2.2.1 EP036 EP036 is comprised of 68.3 acres of gently sloping revegetation that has predominately east aspects. This unit was seeded in 2000 and therefore, has undergone seven growing seasons prior to sampling in 2007. A total of 31 plant taxa were observed in the unit (see Table AB-1). Current annual production across the unit averaged 1,302.6 - pounds per acre in 2007 with perennial grasses and perennial fortis the dominant categories (see Figure 1). Ground cover in EP036 consisted of 65.0% live vegetation, 0.5% rock, 22.7% litter, and bare soil exposure of 11.9%. Perennial cover across the unit averaged 49.4% with annual and biennial cover averaging 15.6%. The dominant taxa were cheatgrass (Bromus tectorum), thickspike wheatgrass (Agropyron dasystachyum), Siberian wheatgrass (Agropyron sibencum), titer milkvetch (Astraga/us titer), and Kentucky bluegrass (Poa pratensis), with 11.5%, 9.8%, 7.4%, 6.5%, and 5.6% average cover, respectively. Woody plant density was determined from 20 belt transects. Density (Table 2) totaled 694 young and mature stems per acre with big sagebrush (Artemisia tndentata) the dominant woody plant. With regard to diversity, EP034 exhibited 5 perennial grasses and 1 perennial forb with between 3% and 50% relative cover. ;, ~, 1~ _ ~ ,y ~. ~ i1. ~~~ ~ Y -- I - canaaa s nark rnwck 1 ~• •r ~, A ~ ~~ - ~~ , ~ ~ ~ 6 ~' r' A 0 ® ® ~® ~, . , ® ® ®~ ® ®' ~ ,k,~„a„ ..,,tiro _ Unit EP036 currently passes the bond release diversity standard of 3 perennial grasses and 1 perennial forb with between 3% and 50% relative cover. This unit easily passes both the cover and production bond release comparisons to the reference areas (see Charts 3 and S). This unit does not presently meet the woody plant density standard of 90% of 1000 stems per acre and will probably not meet this in the foreseeable future due to the heavy competitive grass cover. See Appendix AA -Section 6.3 for a discussion on options and recommendations with regard to woody plant density. Noxious weeds appear to be controlled in this unit, however Canada thistle (Cirsium arvense) and Musk thistle (Caardus nutans) were observed. There are several small patches of annual bromes scattered throughout the unit. Although these bromes currently represent only 15.3% cover, these patches should be monitored/mapped to determine if they are expanding or shrinking. If monitoring reveals expansion, use of the herbicide Plateau is recommended in conjunction with spot reseeding if necessary. It is probable this activity could occur as a normal range management practice without resetting the clock. At present, EP036 is a good example of an improved pasture grassland community with a strong sagebrush component that would contribute to the local system as both cover and foraging habitat for wildlife (especially elk), as well as provide a variety of management opportunities for livestock grazing. Rio Tinto Energy America/Colowyo Mine Page 14 Revegetation Monitoring - 2007 • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • r