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community appears on soils of alluvial origin and sandy to silty texture. These soils <br />were deep, though they often had little horizon development. The community is <br />dominated by hydrophytic and mesic tree species, Acer negundo (boxelder), Picea <br />pungens (Colorado blue spruce), and Populus angustifo/ia (narrowleaf cottonwood). <br />Individuals of these species are often mature and large in stature, forming a canopy <br />which is variable, ranging from dense to open. The riparian community structure is <br />more variable than either the oakbrush or aspen communities, and ranges from open <br />predominantly herbaceous stands to impenetrable Salrx montico/a (willow) thickets. <br />The riparian community composition is influenced primarily by the structure of the <br />drainage channel, and secondarily by adjacent vegetation communities. As with the <br />oakbrnsh and aspen communities, the riparian community is dominated by woody <br />species, with understory strata comprised of numerous graminoids and forts. <br />QUANTITATIVE SAMPLING RESULTS <br />The riparian community within the Sylvester Gulch study area was composed of <br />dominant Acer negurtdo, Picea pungens and Populus angustifolia trees forming a <br />canopy, whose nature (open or closed) was dependent on the topographic character of <br />the drainage at a specific location. The canopy was tall (5-15 meters), and comprised <br />primarily of mature individuals of the dominant tree species. The understory was <br />variable in both species dominance and composition and was comprised of two layers, a <br />medium height shrub layer (1-3 meters) and a low herbaceous layer (<0.5 meters <br />• high). In the majority of locations, the canopy was relatively closed, though both the <br />understory shrub layer and the low herbaceous layer were well developed. <br />Symphoricarpos rotundifo/ius was the only shrub species which was present above the <br />three percent relative cover threshold. Poa pratensis and Dacty/is g/omerata <br />(orchazdgrass) dominated the herbaceous layer. The riparian community contained the <br />highest number of species of the three communities sampled (43), with greater numbers <br />of forts and graminoids than either the aspen or oakbrush communities. <br />Four lifeforms were encountered during the sampling of the riparian community. They <br />included graminoids, forts, woody shrubs, and trees. Forty-three individual plant <br />species were identified during quantitative cover sampling. Eight graminoid species <br />(including one rush, one sedge, and two species of horsetails) were represented, as <br />were eighteen fort species, thirteen shrub species, and four tree species. As with the <br />aspen community, the riparian community is stratified by species and physiognomy. <br />The dominant tree species form an upper canopy, with shrubs divided into low, <br />medium, and tall strata. Graminoids and forts form a low herbaceous layer close to <br />the ground (< 0.5 meters high). Mahonia repens and Paxistima myrsinites characterize <br />the low or sub-shrubs, Symphoricarpos rotundifo/ius the medium shrub layer, and <br />Crataegus rivularis (hawthorn), Betula fontinalis (river birch), and Salix monticola <br />representing the tall shrubs. Notably, thirteen of the forty-three species encountered in <br />. the riparian community were unique to this community. Of the species encountered, <br />perennials were dominant, with one biennial and one annual present. One warm season <br />-17- <br />