Vegetation Distribution


A number of studies have focused on describing the vegetation distribution within Red Butte Canyon (Kleiner and Harper 1966, Swanson, Kleiner, and Harper 1966, Kleiner 1967). There is a strong xeric to mesic elevation gradient, with lower portions of the canyon dominated by a spring-active grassland community and the upper portions of the canyon typically consisting of summer-active scrub oak, aspen, and coniferous forest communities (Figure 10). Composition within each of these communities is not constant, but instead species vary in their importance within a community type as orientation and elevation change. These elevation gradients represent a continuum of moisture availability, with high temperatures and low precipitation amounts at lower elevations making coniditions more xeric, while slope orientations less soustherly in exposure become progressively more mesic within an elevation band. Soil type (Figure 5) and depth also play a major role in affecting plant distribution by providing variation in the water-holding capacity of the substrate. The distribution of the scrub-oak community to the highest elevations within the canyon is most likely related to soil conditions, since at high elevations scrub oak persists on south-, east-, and west-facing slopes that would normally be expected to be dominated by aspen if it were not for the very shallow, rocky soils that typify these elevations within Red Butte Canyon.


Fig. 10. Distribution, by elevation, of the major plant communities in Red Butte Canyon.
Fig. 11. A comparison of the plant cover in open grassland communities of different elevations in Red Butte and Emigration canyons. Adapted from Cottam and Evans (1945).
Red Butte Canyon has been largely protected from grazing since its acquisition by the U.S. Army almost a century ago. The consequence of this lack of grazing pressure at lower elevations is a recovery to near pristine levels, and this is clearly reflected in the early community analyses of Evans (1936) and Cottam and Evans (1945). Within the scrub oak and grassland communities of Red Butte Canyon and adjacent Emigration Canyon, a canyon annually exposed to sheep grazing, there are large differences in plant density (Figure 11). Emigration Canyon was originally described by early pioneers as having a dense vegetation at lower elevations. However, grazing not only reduced that cover but also increased the fraction of the plant cover occupied by ruderal, weedy species (Cottam and Evans 1945). While plant density in Red Butte Canyon may be greater and weedy species composition lower as a result of reduced disturbance and grazing, the canyon is not free of these weedy components and historical effects (as noted in early sections). Dam construction during the 1920s and other U.S. Army activities within the lower portions of Red Butte Canyon have resulted in sufficient disturbance that many ruderal, weedy species, such as Grindelia squarrosa (curly gumweed), Lactuca serriola (prickly lettuce), and Polygonum aviculare (knotweed), are now common.

Samuelson (1950) conducted an analysis similar to that of Cottam and Evans (1945) on the algal components of the streams in Red Butte and Emigration canyons. He observed that as a result of livestock grazing and human settlement, sediment load and turbidity were much greater in Emigration than in Red Butte Creek. The consequence of this stream-quality difference was the dominance by algal genera in Emigration Creek that are turbidity tolerant, such as Oscillatoria and Phormidium. Conversely, in the clear waters of Red Butte Creek, owing to the greater light penetration into that stream. At the same time, Whitney (1951) compared the distributions of aquatic insects in the two streams. He found that densities of aquatic insects were greater in Red Butte Creek. Of those insects persisting in Emigration Creek, there was a preponderance of species characterized by gills protected from silt, which would better allow them to tolerate the more turbid conditions in Emigration Creek.

More on Plant Ecology

• Phenology
• Adaptation