2010-12-17_REVISION - C1981019 (160)

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Five sub-types of the Bottomland community were identified (Wetland, Mountain Shrub, Sagebrush, Riparian Bottom, and Grassland) during mapping and field verification and are described below. Owing to its disproportionate importance as a habitat, as well as jurisdiction by the U.S. Army Corps of Engineers under the Clean Water Act, the wetland subtype is fully described in Section 3.7.4. as a paraphrased section from the Wetland Delineation submitted to the Corps. The mountain shrub subtype is simply described as invasions from upland sites into the numerous concave basins of the various headwater drainages throughout the study area. These invaded areas exhibit an identical character and ecological attributes as is described for the larger community presented under Section 3.5. The sagebrush and grassland sub-types generally occupy the relatively flat floodplain terraces extending from the toe of the adjacent slopes to the creek channel or wetland. If recent burning or sagebrush removal has occurred, the area has been designated as grassland. These areas are variably dominated by perennial wheatgrass species (Agropyron sp.), Great Basin wildrye (Eiymus cinereus) (at higher elevations), or annual bromes with occasional sagebrush or rabbitbrush reinvasion. The grasslands in the Bottomland community differ from upland Grassland communities in that they exhibit substantially higher production and cover values due to the increase soil moisture levels. The sagebrush sub-type is visually dominated by basin big sagebrush with lower densities of rubber rabbitbrush, mountain snowberry and silver sage. The recent drought along with channel "down-cutting" has reduced the alluvial water table which appears to have contributed to a substantial die-off of basin big sagebrush on the terraces, most notably in the Wilson Creek drainage. The riparian bottomland sub-type is highly variable and scattered and includes the linear channel banks adjacent to the streamside and expanded streamside wetlands where an overstory of boxelder (Acernegundo) is often evident. 3.2.2 Bottomland Reference Area . The Bottomland reference area is located along Wilson Creek just external to the northeast portion of the study area (see Map V1). This area was selected as a reference area because of its easy access, low probability of future disturbance, and it represents a mix of sagebrush and grassland sub-types within its boundaries (no areas could be located that also included the riparian bottom subtype owing to its more scarce distribution). Review of Table V4 and Chart V1 indicates that the average vegetation cover of the Bottomland reference area was 64.2%. Litter and rock provided an average of 31.7% and 0.5% of the ground cover, respectively, while bare ground exposure averaged 3.7%. The dominant plant species were cheatgrass, western wheatgrass, Sandberg bluegrass (Poa secunda), basin wildrye (Eiymus cinereus), and thickspike wheatgrass with 27.3%, 9.6%, 7.5%, 4.6%, and 3.2% of the ground cover, respectively. Perennial plants (excluding noxious weeds) contributed 56% of the total plant cover (35.8% average cover) while annual species and noxious weeds contributed 44% and 0.0% of the composition, respectively. Perusal of Table V10 indicates that a total of 4 perennial species contributed CEDAR (CIR2IEIEKA ?FUMS,INC. Page 17 2005 Collom Vegetation Survey