The vegetative appearance of the watershed is dominated by sagebrush. Three species cover significant areas on the watershed. Big sagebrush (Artemesia tridentata ssp. tridentata) is the dominant species below 1370 meters but is present in all associations and at all elevations. This single species is present at both extremes of elevation that occur on the watershed. Below 1370 meters it occurs on all aspects and slopes. Between 1370 meters and 1740 meters it is most common on moderate to steep north- and east-facing slopes. Above 1740 meters it occurs on level, moderate, and steep south- and west-facing slopes. The soils on which big sagebrush occurs are moderate to well drained and profile depths vary from very shallow to very deep.
Big sagebrush is excluded only from areas of alkaline soils and under tree canopies where sufficient light does not penetrate to the ground level. In the areas of alkaline soils dominated by greasewood (Sarcobatus vermiculatus), big sagebrush occurs as inclusions on well-drained rises that are slightly above the surrounding terrain. Big sagebrush does not occur under closed canopies of bitter cherry (Prunus emerginata), quaking aspen (Populus tremuloides), Douglas fir (Psuedotsuga menziesii ssp. glauca), or alpine fir (Abies lasiocarpa). It is a prominent associate of these species, however, in more open stands.
Low sagebrush (A. arbuscula) is the dominant sagebrush species above 1370 meters. It occurs most commonly on moderately sloping west- and south-facing slopes with poorly drained soils. The restricted drainage of these soils is caused by both a fine textured A horizon and an impeding B horizon that varies from 25 to 46 cm below the surface.
The areas in which low sagebrush grows are subject to high winds during the winter. Depths of accumulated snow is limited by the height of low sagebrush, which is about 38 cm. Maximum snow accumulation takes place early in the winter, but because of the west and south exposures of these sites, differential melting occurs. Snow reaccumulates with subsequent snowstorms and the differential melting process is repeated. By midwinter the poorly drained soils are supersaturated. In late winter free water collects beneath the thin crust of snow. During late winter and early spring, infrequent rain-on-snow storms immediately generate runoff and erosion from these sites.
Vaseyana sagebrush (Artemesia tridentata ssp. vaseyana) occurs above 1830 meters on moderate to steep north- and east-facing slopes. In these areas snow accumulates to depths greater than 150 cm and persists into late spring. Soils are very well drained and are commonly deep (300 to 450 cm). Significant deep percolation and local groundwater recharge occurs in these areas.
Shrubs and Trees
Superimposed on the sagebrush dominated landscape is a discontinuous pattern of other plant associations. Specific soil conditions are responsible for some of the patterns that occur in plant communities at lower elevations and certain lithologic types influence the distribution of particular associations in other areas of the watershed. However, the majority of patterns of plant associations on the watershed correspond to the discontinuous microclimates created by the complex topography and relief.
Specific soil conditions, in particular, influence the distribution of major plant associations representing the Great Basin Desert communities. These plant associations include shadscale (Atriplex confertifolia), greasewood, and spiny hopsage (Grayia spinosa). These associations are confined to alluvial soils in the valley floor. Shadscale grows in saline soils, while spiny hopsage occurs in the same area but in less saline soils. Greasewood grows in deep alkaline soils where its roots may reach the more saturated underlying clays. Desert sage (Salvia dorii spp. carnosa) grows on bare basalt outcrops at the lowest elevations and budsage (Artemesia spinescens) is present on small areas in which free lime is found in the soil profile.
The plant associations most sensitive to lithology are the bitterbrush (Purshia tridentata) and mountain mahogany (Cercocarpus ledifolius) associations. Both are developed best on coarse-textured, well-drained soils. These soils are usually found where the parent material is granite or highly fractured glassy volcanic. Bitterbrush is found at all elevations, growing in soils derived from either lithologic type. Mountain mahogany, however, in most cases is confined to granite outcrops that occur at all elevations.
Distinctive forest are found at the high elevations of the watershed. Stands of second-growth Douglas fir occur on the north- and east-facing slopes above 1830 meters, while alpine fir is found on the same aspects at higher elevations. These forests have both a small vertical and horizontal distribution, but where they do occur, it is mainly in response to generally deeper snow accumulations in the forest areas themselves and below very deep snowdrifts above the forest areas. These large drifts form in the lee of the highest ridges along the divide of the watershed.
The two most abundant grass species on the watershed are bluebunch wheatgrass (Agropyron spicatum) and Idaho fescue (Festuca idahoensis). Bluebunch wheatgrass occurs at all elevations and on all soils. It attains it best development, in terms of forage yield, between 1220 and 1525 meters. At all elevations below 1220 meters, cheatgrass (Bromus tectorum) is its most abundant understory associate; between 1220 and 1525 meters, Sandberg bluegrass (Poa secunda) and squirreltail (Sitanion hystrix) are the common understory associates. Above 1525 meters, Idaho fescue and bluebunch wheatgrass are found together with Idaho fescue as the dominant grass species. June grass (Koeleria cristata), wheatgrass (Agropyron spp.), and bluegrass (Poa spp.) contribute to higher forage yields on north- and east-facing sites at higher elevations.
Riparian vegetation occurs continuously along Reynolds Creek and Dobson Creek, its main tributary. Cottonwood (Populus trichocarpa) and willow (Salix spp.) occur along the entire length of the main channel. Chokecherry (Prunus virginiana) and bitter cherry are common species at intermediate elevations. Maple (Acer spp.) and alder (Alnus spp.) occur at the highest elevations. For the same relative elevations, these species are also found around the many springs in the watershed.
Northeast Facing Slopes: Typical Associates
Microclimates produced by complex topography vary continuously with slope-aspect-elevation combinations. The most distinctive microclimates at all elevations are associated with the steep northeast-facing slopes. Two main effects contribute to the distinctive character of the radiant energy and water balance of these sites. The steep northeast-facing slopes receive a minimum of radient energy at this latitude, and because of the prevailing southwesterly direction of winter storms, these same sites receive significantly more precipitation than any other slope-aspect site at the same elevation. At higher elevations the effect of depth of the snow accumulated at these sites is singly the most significant factor controlling the character of the plant associations growing on these sites.
Using the steep northeast-facing slopes as a reference, the typical plant associations that would be expected to occur at a given elevation are as follows. Beginning with an elevation of 1220 meters, the plant association is generally a robust stand of bluebunch wheatgrass and big sagebrush. At 1370 meters, Lupine (Lupinus spp.) is a distinctive addition to the former association. Less bluebunch wheatgrass is found at 1525 meters but currant (Ribes spp.) and snowberry (Symphoricarpus spp.) assume co-dominance with big sagebrush. At the slightly higher higher 1680 meters elevation, big sagebrush, vaseyana sagebrush, and snowberry encircle clonal stands of quaking aspen on the basalt soils. In contrast, the same association of species encircles clonal stands of bitter cherry on the glassy volcanic derived soils that occur at the same elevations.
An interesting zonation of associations occur at 1830 meters composed of big sagebrush, vaseyana sagebrush, and snowberry growing in a crescent below clonal stands of quaking aspen; immediately above the aspen stands a closed canopy of Douglas fir occurs. At 1980 meters, this same pattern of zonation is repeated but with another tree species, alpine fir, occurring above the Douglas fir. Dense stands of alpine fir grow at 2135 meters to the exclusion of all other major species. Above the alpine fir, only the small mat-forming alpine plant, creeping sibbaldia (Sibbaldia procumbens) can withstand the cold soil temperatures and the very short growing season of the nivation cirques.