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West Elk Mine <br />• for physical factors, and predation. Importance of individual and combinations of factors vary for <br />each plant species and vegetation community. Within the environmental study azea great variation <br />exists in the physical factors identified above. Large elevational gradients and complex topography <br />affect light, water and soil availability. Geologic mass-wasting destroys communities and opens <br />avenues for vegetation re-invasion. Seasonal temperature variation, coupled with seasonal light <br />intensity determines length of growing season. <br />Vegetation communities are not always distinct units. Variation along environmental gradients <br />causes mixtures and blending of the communities (Whittaker 1970). For these reasons, <br />identification of the nine vegetation communities within the environmental study area is not always <br />precise. While mapping is based on the predominant plant species within a vegetation community, <br />locations occur where the mixture of vegetation communities is a complex mosaic. hi these <br />instances, more than one community is identified in these ecotones. The following descriptions of <br />the vegetation communities present the chazacteristics of the community in its most representative <br />state. <br />Vesetation Communities of the West E-k Mine Study Area <br />In June 1976, a survey of plant species present within the environmental study area was conducted. <br />A total of 166 species were collected and identified (Exhibit 31). Of this total, 7 were classified as <br />trees, 24 as shrubs, and 135 as herbaceous. Of the 135 herbaceous species, 22 were classified as <br />grasses or grass-like. Twenty-one species, or 13 percent of the total, represent species introduced <br />• from outside North America. All trees and shrubs were native. Nine vegetation communities were <br />mapped in the environmental study azea. The distribution of these vegetation communities is shown <br />on Map 42. Each type is described below. <br />Edaphic and topographic relationships of each vegetation community over the study azea aze <br />discussed as well as site characteristics of the transect sampled within the type. Cover and height of <br />principal species of tree, shrub, and herbaceous strata are presented within each vegetation <br />community. <br />All vegetative communities identified on the West Elk Mine study azea aze representative of lazge <br />areas within the West Ells Mountains. Several unusual endemic species are found in the vicinity of <br />Gunnison, Colorado (Harrell, 1969) further to the southeast. These aze extremely unlikely to occur <br />in North Fork Gunnison Valley because the later has experienced a different geologic and climatic <br />history. <br />Oakbrush <br />The oakbrush community is the predominant vegetation community found in the 1976 study area. <br />This community is distinguished by the dominance of two shrub species, serviceberry (Amelanchier <br />alnifolia) and Gambel oak (Quercus gambelit~. Individuals of the two species occur in roughly <br />equal numbers on most sites and range in height from 2-5 m (6-15 ft.). Other common associates <br />aze snowbeny (Symphoricarpos oreophilus) and chokecherry (Prunus virginiana). <br />• Oakbrush occurs from the north-facing slopes above the North Fork of the Gunnison River, <br />southward on upland azeas to the vicinity of Beaver Reservoir, where the type is lazgely replaced <br />2.04-137 Revised November 2004 PRIG <br />