|
486 stems per acre in the extended reference area (Appendix 10A, Table 10A-8). Aspen
<br />observed during sampling of this type ranged up to about 22 m in height with individual stem •
<br />ages as old as 106 years. Most typical stands had tallest trees in the range of 1 5 to 1 B m,
<br />with diameters up to about 25 cm and associated maximum ages of 50 to 60 years. On most
<br />sites, an annual diameter growth rate of approximately 0.4 cm (diameter at breast height Idbh])
<br />was obtained, with a few on the drier, more marginal sites exhibited rates as low as slightly
<br />less than 0.1 cm Idbh) per year.
<br />Mountain Brush Vegetation Type (Photos 9 through 16)
<br />Dominance of the affected area of vegetation cover in this type (Appendix 108, Table tOB-11 is
<br />held by the same three shrub species (Saskatoon serviceberry, black chokecherry, and
<br />mountain snowberryl that dominate the understory of the Aspen Forest type, with one
<br />additional species, Gambel's oak IQuercus gambe/ii/, which has relatively little shade tolerance.
<br />The other species occurring commonly included Oregon grape IMahonia repensl, Woods' Rose
<br />(Rosa woodsiil, and big sagebrush Iseriphidium tr/dentatum and S. vaseyanuml, Quaking aspen
<br />occurs very sparsely in the unit as mapped with only 0.5 percent of total vegetation cover.
<br />Next to native shrubs, the most abundant lifeform was native perennial forbs, which totaled
<br />26.3 percent of total vegetation cover. With sixty-eight species observed, this lifeform had
<br />even greater species richness than the Aspen Forest type. The largest contributors to total
<br />vegetation cover in the native perennial forb lifeform were western yarrow, nettleleaf •
<br />gianthyssop, showy daisy lErigeron speciosusl, showy goldeneye (Heliomeris multiiloral, white-
<br />flower peavine, chiming bells, sweet Cicely /Osmorhiza chi/ensisl, common Yampa IPerideridia
<br />gairdneril, James' starwort IPseudoste/%ria jamesianal, and American vetch. Native perennial
<br />cool season grasses were almost twice as abundant in this type as in Aspen Forest.
<br />Comprising a total of 14.5 percent oT total vegetation cover, the most abundant were blue
<br />wildrye and Agassiz bluegrass. Other common species present included Nelson needlegrass
<br />/Acnatherum nelsoniil, oniongrass lBromelica bulbosal, mountain brome ICeratochloa
<br />marginatal, and slender wheatgrass. Introduced perennial coot season grasses were very
<br />sparse, providing less than measurable cover. The most frequently present was common
<br />timothy IPh/eum pratensel which occurred in about one-quarter of sampled stands. Native
<br />annual land biennial) forbs were somewhat more common than in the Aspen Forest type,
<br />comprising 2.0 percent of total vegetation cover. The most commonly occurring of these
<br />species were Fremont goosefoot (Chenopodium /remon[iil, linearleaf collomia ICoIlomia
<br />/inearisl, and Douglas knotweed IPo/ygonum doug/asirl.
<br />Totat vegetation cover in the portion of the Mountain Brush vegetation type to be affected by
<br />the Seneca II-W South Extension (Appendix 10B, Table 10B-11 was 86.7 percent, while
<br />standing dead, litter, bare soil, and rock were 0.4, 9.3, 3.6, and 0.0 percents, respectively, By
<br />comparison, in the unaffected )extended reference) area portion of the Mountain Brush •
<br />vegetation type (Appendix 10B, Table 108-21, total vegetation cover was 82.3 percent, while
<br />54 Revised 9/98
<br />
|