2009-03-27_REPORT - C1981019 ‎(7)‎

• Permit No: C1981019
• IBM Index Class Name: REPORT
• Doc Date: 3/27/2009
• Doc Name: 2008 AHR & ARR Exhibit 9A
• From: Colowyo Coal Company
• To: DRMS
• Annual Report Year: 2008
• Permit Index Doc Type: Hydrology Report
• Email Name: JRS
• Media Type: D
• Archive: No

2.4.2 WPO10
WPO10 is comprised of 5.7 acres of gently sloping
revegetation that has predominately a westerly aspect.
This unit was seeded in 2001 and therefore, has
undergone seven growing seasons prior to sampling in
2008. A total of 28 plant taxa were observed in the
unit (see Table AB-1). Current annual production
across the unit averaged 1,569.2 pounds per acre in
2008 with annual grasses and perennial grasses the
dominant categories (see Compendium 6). Ground
cover in WPO10 consisted of 77.1% live vegetation,
0.7% rock, 20.7% litter, and bare soil exposure of
1.6%. Perennial cover across the unit averaged only
21.6% with annual and biennial cover averaging 55.4%
and noxious weed cover 0.1%. Dominant taxa were
cheatgrass, thickspike wheatgrass, Siberian wheatgrass
(Agropyron sibericum), western wheatgrass, and
crested wheatgrass, with 52.6%, 7.7%, 3.7%, 2.9%,
and 2.3% average cover, respectively. Woody plant
density was determined from 20 belt transects.
Density (Table 2) totaled 40 young and mature stems
per acre with four-wing saltbush the dominant woody
plant. With regard to diversity, WPO10 exhibited 3
perennial grasses and 0 perennial forbs with between
3% and 50% relative cover.
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Unit WPO10 currently fails the bond release diversity standard of 3 perennial grasses and 1 perennial
forb with between 3% and 50% relative cover (see Chart 6) because it does not exhibit a dominant forb.
This unit also fails the cover bond release comparison to the reference areas (see Charts 3 and 4) but
passes the production comparison. 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 7.3 for a discussion on options and
recommendations with regard to woody plant density. An occasional noxious weed (musk thistle) was
observed in this unit but overall noxious weeds are controlled. There are several significant patches of
annual bromes scattered throughout the unit. Currently, these bromes represent only 53.8% cover, and
according to monitoring presented on Compendium 6 the populations are growing at a slow pace.
At present, WPO10 is a pasture that is dominated by annual bromes, with perennial grasses present.
Annual cover has been steadily increasing over this unit's sampling history (2003, 2005, 2008). Given
the propensity of annual brome to outcompete perennials once it has reach a given threshold level, it
would be prudent to treat the unit with Plateau or Oust (herbicide for annual grasses) to give more
perennials a chance to germinate and grow within this unit. If treatment with either of these herbicides
is undertaken, special care must be followed to preclude damage to the perennials.
Rio Tinto Energy America/Colowyo Mine Page 22 Revegetation Monitoring - 2008