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' CNAPTERTHREE affected Environment Pinyon-Juniper Association The Pinyon-Juniper Association occws on a wide range of soils, elevations, and exposwes and is limited primarily by semi-arid or cool-mesic climatic conditions and saline-alkaline soils. This vegetation type appazently has a competitive advantage over other vegetation types and is the climax association on xeric ridgetops with shallow soils (BLM 1994). This community dominates upland hillsides at the Piceance Site, occumng primarily on Rentsac channery sandy loam soils, the Torriorthents-Rock outcrop complex, and the minor areas of the Redcreek- Rentsac complex soils that occw on the Piceance Site. This community is used extensively as winter habitat for mule deer and summer habitat for many small animals and birds (SCS 1982). The Pinyon-Juniper Association is characterized by low growing pinyon pine and Utah juniper woodlands. Overstory varies from sparse (ZO-50 percent cover) to open (50-80 percent cover) woodland, and understory shrub and grass-forb productivity generally varies inversely with overstory closure (BLM 1994). Rocky Mountain juniper is dominant in mesic draws and slopes. The understory described by Tiedeman and Terwilliger (1978) consists of Indian ricegrass, mutton bluegrass, western wheatgrass, slender wheatgrass, and needle-and-thread. Mountain mahogany, big sagebrush, and flowery phlox are the dominant shrubs on the sites with more favorable soil and climatic chazacteristics. On sites where rock outcrops occupy more than 30 percent of the azea, the dominant shrubs are common snowberry, Douglas rabbitbrush, antelope bitterbrush, creeping barberry, and mountain mahogany. Forbs are not dominant in any of the Pinyon-Juniper communities, but plains pricklypeaz is common at higher elevations. The Pinyon-Juniper association comprises 1,916 acres (47 percent) of the Piceance Site. Chained Pinyon-Juniper Community The Chained Pinyon-Juniper community is a result of vegetation manipulation performed in 1965 to provide increased livestock forage. Dominant vegetation includes big sagebrush, Indian ricegrass, bluebunch wheatgrass, needlegrass, and bluegrasses, with scattered small pinyons and junipers (BLM 1982). This community occws only on the flatter ridgetops in the southwest section of the lease area in the vicinity of the proposed processing plant. Soils in this area are Rentsac channery loam or Redcreek-Rentsac complex on which the potential plant community is as described above for the Pinyon-Juniper Association. The Chained Pinyon-Juniper community comprises 311 acres (8 percent) of the Piceance Site. ' Sagebrush Association The Sagebrush Association is influenced by many interacting and independent ecological factors including climate, soils, topography, fire history, and grazing history. The overstory vanes from open to completely closed, with understory species diversity and density inversely related to overstory closwe (BLM 1994). Wyoming sagebrush is 2 to 3 feet tall and occupies Yamac loam soils on the ridges; basin big sagebrush is typically 6 to 8 feet tall and occupies the valleys. t The Sagebrush Association is usually an open stand of sagebrush with an understory of grasses, including western wheatgrass, mutton bluegrass, cheatgrass brome, needle-and-thread, Indian ricegrass, and various sedges (Tiedeman and Terwilliger 1978). Other herbaceous species adapted to xeric conditions that may occw at lower elevations include squi~eltail, Colorado Vegetation 3-27