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~. <br />Europe and Asia. It is these introduced species that are th~a aggressors <br />• in disturbed sites, and that often delay the invasion of disturbed ground <br />by native plant species. <br />Major plant species in disturbed areas include douglas-'Fir, <br />ponderosa pine, golden aster, gumweed (Grindelia squarrosa), giant <br />ragweed (Ambrosia trifida), burning-bush (Kochia iranica), goosefoots <br />(Chenopodium ssp.), western ragweed (Ambrosia psilostachya), sticky aster <br />(Machaeranthera pattersonii), great mullein (Verbascum thapstis), sage <br />(Artemisia dracunculus), thistle (Carduus nutans ssp. macrolc~), <br />sweet clovers (Meliolotus ssp.), plantains (Plantago ssp.), I:notweeds <br />(Polygonum ssp.), cheatgrass (B. tectorum), Canada wild-rye I,Elymus <br />canadensis), and amaranths.(Amaranthus ssp.). Over 50% of tfie relative <br />cover in disturbed sites is bare ground. Less than 2Y relative cover <br />is litter in disturbed ground. <br />• Summary of Mine Site Vegetation: <br />The SE1/4 of Section 25 supports a very diversified flora <br />(some 280+ different species in 69 different plant families). <br />Five principal stand-types of vegetation occur at the study <br />site: (1) grassland; (2) mountain mahogany; (3) douglas-fir:, <br />4) ponderosa pine; (5) riparian. A sixth "stand-type" may tie <br />considered for disturbed areas (roadcuts, etc.). Boundaries <br />between stand-types are often diffuse intergradations of one type <br />into another, except the riparian habitat where the boundariE~s are <br />quite delineated near the Ralston Creek water table. <br />Several factors influence the richness of the flora four~d at <br /> the site. Firstly, the project site (SEl/4 of Section 25) lies <br />• in a transition zone between two major ecosystems, the plains-grassland <br />~-10 <br />