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lJ CNAPTERTHREE Affected Enui~onment communities aze important because they support higher population densities and greater diversity of both plant and animal species than any other plant community in the study area (BLM 1994). Mule deer, cottontail rabbit, coyote, bobcat, ducks, geese, and other native birds find food and shelter in riparian communities (SCS 1985). Wetlands aze limited in the study azea and occur mainly on the floodplains of major streams. Most wetlands in the study area aze wet meadows dominated by a mixture of grasses, sedges, and ntshes, including reed canazygrass, Nebraska sedge, Richazdson muhly, redtop, timothy, Baltic rush, streambank wheatgrass, foxtail bazley, narrowleaf sedge, and spikerush. Wetlands are discussed further in Section 3.9. Plant Communities of Special Concern Several plant communities that occur in the vicinity of the pipeline corridor aze considered to be "vulnerable' or "imperiled" in the state and throughout their ranges (Colorado Natural Heritage Program 1998). These plant communities and their dominants include: Montane Riparian Deciduous Forest (Ater negundo/Prunus virginiana), Xeric Sagebrush Shrublands (Artemisia tridentate ssp. wyomingensis/Oryaopsis hymenoides), Cold Desert Shrublands (Atriplex confertijolia/Agropyron spicatum), Narrowleaf Cottonwood/Skunkbrush (Populus ongustifolia/ Rhus trilobata), and Mixed Mountain Shrublands (Quercus gambelii/Cercocarpus montanus/ Carex geyeri). Documented locations of these five plant communities along the pipeline comdor, to section, aze shown in Figure 3.7-2a, b, and c. 3.7.3 Parachute Site The Parachute Site occupies an existing, inactive industrial site that has been extensively disturbed under previous development. Historically, the vegetation community was predominantly grasslands (SCS 1985}. Now, significant azeas within the site aze paved, and spazse vegetation is predominantly weeds. The following plant species were observed to dominate disturbed azeas at the Pazachute Site during a site visit in eazly June 1998: yellow sweet clover, gumweed, annual sunflower, cheatgrass, pennycress, prickly lettuce, and bindweed. Less disturbed azeas between the existing developed azea and Parachute Creek support relatively dense stands of rabbitbrush, with some wild rye and wheatgrass (Steigers 1998b). 3.7.4 Noxious Weeds A noxious weed is defined as an undesirable plant that interferes with management objectives of a given azea and results in deterioration of ecological conditions. Noxious weeds and their continued encroachment on both public and private lands represent a serious threat to BLM's objective to maintain healthy and diverse ecosystems and rangeland on BLM-controlled land. They can also result in significant costs to private landowners. Typically, noxious weeds are opportunistic plants that invade disturbed or recently revegetated azeas where, because they aze particularly adapted to harsh conditions, they can become established and spread quickly and soon displace native plants. An infestation of noxious weeds can reduce agricultural productivity Vegetation 3-31