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• Y.1.2 General Specifications and Environmental Limitations. The vegetation of the Intermountain <br />Region is xeric in character and, as such, is adapted to conditions of extreme temperature ranges, low <br />precipitation, and poor-to-toxic soil environments. Revegetation plans must be flexible and be designed to <br />work within the constraints of these limiting factors, rather than to attempt to counteract the effects of <br />environment. The primary factors driving the design of the revegetation plan are; <br />a. Soit moisture (or lack thereof) is a limiting factor with a mean annual precipitation of about 9.5". <br />The relatively wet seasons occur in early spring with April-May receiving the greatest amount of <br />early precipitation and again in the fall with September-October being the wettest fall months. <br />Precipitation received during the summer months is rapidly lost to evapotranspiration with <br />daytime high temperatures averaging around 90 degrees F. <br />b. Soils are generally poor in quality with weak structure, low fertility, and contain little organic <br />matter. Salinity can also be a limiting factor on some soils. <br />c. Competition from weedy annual grasses and (orbs can be severe. Cheatgrass (Bromus <br />tectorum), Russian thistle (Salsola iberica), Kochia (Kochia iranica), and Tumble mustard <br />(Sisymbrium altissimum} have presented the greatest amount of competition in the past. <br />d. The requirement to establish a shrub component on the reclaimed areas also influences the <br />design of the revegetation plan. Special consideration must be given to shrub establishment <br />• since an aggressive stand of annual or perennial grasses can severely limit shrub <br />establishment. <br />e. The resulting stand of vegetation must be suitable for the postmining land use. <br />General revegetation practices used to address these factors include: <br />a. Species are selected that are adapted to the area. Consideration is given to many factors <br />including drought tolerance, compatibility with soils being revegetated, origin, longevity, <br />competitiveness, and desirability for the postmining land use. The seed mix would generally <br />include numerous species with diverse traits. Short lived perennials or annuals are included to <br />assist in initial site stabilization and to provide competition against the aggressive weedy <br />annuals. <br />Species with medium longevity are included to help maintain competition with the weedy <br />annuals and to aid in the long term stability of the site. Some species in this classification may <br />persist in the stand for many decades by reseeding themselves. Others will eventually be <br />replaced by slower maturing but longer lived, typically native, species. <br />The long lived species comprise the majority of what is generally termed the 'permanent' <br />vegetation. These species typically are slow to establish and/or mature but are very persistent <br />once established. <br />• <br />Mid-Term Review 2002 (8/2002) V-30 <br />