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IRIS <br />MITIGATION AND DESIGN, INC. <br />SCHWARTZWALDER MINE PHASE 1 - UPSTREAM CUTOFF WALL AND LOW FLOW BYPASS <br />PIPELINE - BIOLOGICAL ASSESSMENT <br />4.1.2 Riparian Habitat <br />Although previously impacted by mining practices, many of the riparian habitats have recovered and <br />currently form a narrow but lush strip of vegetation along Ralston Creek (see Figure 2 and Appendix <br />B). Much of the riparian overstory (32 percent relative cover) is dominated by hybrid cottonwood <br />(Populus X acuminata), which can grow to a height of 30 feet or more. Growing to a height of <br />approximately 19 feet, narrowleaf cottonwood (Populus angustifolia) comprises 3 to 6 percent relative <br />cover of the canopy. Willows are also prevalent, comprising 35 to 45 percent relative cover of the <br />vegetation over 1 1 /2 feet tall. <br />In addition to its well- vegetated character, the area's riparian habitat supports a large number of <br />different species. In addition to the species listed above, the riparian habitat supports the following <br />overstory species: plains cottonwood (Populus sargentii), juniper (Juniperus scopulorum), thin -leaf <br />alder (Alnus incana), Rocky Mountain maple, peachleaf willow (Salix amygdaloides), ponderosa pine, <br />and Douglas -fir. The larger tree species are found sporadically within the riparian corridor and rarely <br />form a forest. The shrubby understory of the riparian habitat is dominated by the following: willows <br />(Salix spp.), common gooseberry (Ribes inerme), chokecherry (Prunus virginiana), wax currant, three - <br />leaf sumac (Rhus trilobata), snowberry, and wild rose. The riparian corridor also supports a diverse <br />understory of grasses and forbs that cover relatively large areas (75 to 80 percent relative cover) within <br />the riparian zone. Common grasses include: crested wheatgrass, a variety of other wheatgrasses <br />(Agropyron and Elymus spp.), smooth brome, American mannagrass (Glyceria maxima), Kentucky <br />bluegrass (Poa pratensis), and orchardgrass. <br />Well- vegetated riparian habitats, such as those found in the Site, are ecologically and socially <br />important for their ability to provide a myriad of functions. The riparian corridor in the Site is expected <br />to provide all of the following functions to varying degrees: improved creek temperature (through <br />shading), a corridor for wildlife movement, wildlife cover and nesting, minor floodwater attenuation, <br />organic matter input/forage for downstream fish and wildlife, erosion protection, surface water filtering, <br />and sediment storage. <br />4.2 Habitat Description in Proposed Work Area <br />The proposed work area has been historically impacted by mining practices and consists of <br />approximately 325 linear feet of Ralston Creek of which 40 feet is an unpaved upland road crossing of <br />the creek. Within the proposed work area, Ralston Creek averages approximately 1 to 2 feet deep by <br />Page 25 August 2011 <br />