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diameter sizes, densities and vigor vary depending on the available moisture and soil characteristics of the site. All communities, however, tend to mature and approach senesence within approximately 60 years. Senesence is common in all size classes, and an average of 15 percent of all standing trees are dead. The height of the aspen trees is dependent on soil fertility and available moisture. - Tree heights range from 16 meters on the favorable sites (Routt Series) to 10 meters on the less favorable sites. Densities ranged from 64 to 155 per quadrat (375m2), or averaged 1,025 trees/acre. These densities are not high because most of the communities are approaching maturity. However, aspen reproduction rates, although variable, are generally high compared to other areas of Colorado. Survival of saplings appears to be related to available moisture, which varies seasonally, and with grazing pressure. Understory shrub cover, which averaged 54 percent, is relatively dense in the aspen understory. Five shrubs occur in the aspen stands: serviceberry, rose, snowberry, chokecherry, and gooseberry. serviceberry and snowberry are dominant, as expressed in percent cover. However, the dominance of these two shrubs varies depending on habitat conditions. snowberry has a preference for partially shaded areas and coarse substrates, while serviceberry grows best in deep loamy soils and can tolerate higher intensifies of light. • The herbacous flora of the aspen community understory is limited to 29 species: 26 forbs, 2 grasses, and 1 sedge. Total herbaceous cover is low in the stand type. Graminoids (grasses and grass-like plants*) generally cover a greater percent of the area than forbs. Total herbaceous cover averages 20 percent. Forbs average 8 percent in cover, while graminoids average 12 percent. Only three graminoids are present in the aspen munity: blue wild-rye, EZymus gZaucus; bluegrass, Poa agassizensis; and elk sedge, Carer geyeri. Forbs character- istic to all stands include: yarrow, AchiZZea Zanulosa; giant-hyssop, Agastache urticifoZia; bedstraw, CaZium boreale; dandelion, Tararacum sp.; and vetch, Vicia americans. False forget-me-not, Hackelia floribunda, with an average cover of two percent is the most abundant forb in the community. Other forbs with a one percent cover include: aster, Aster sp.; fireweed, Chamerion angustifolium; western tansy mustard, Descurainia richardsonii; and valerian, Valerians occidentaZis. • Elk sedge, Carer geyeri, is the only "grass-like" plant in the flora of the site. -8-