Date of Award:
Doctor of Philosophy (PhD)
Department name when degree awarded
Neil E. West
The vegetation of Canyonlands National Park, Utah, has been described from 157 samples located throughout the Park. Species frequency, density and cover were recorded along with measurements of soil thickness, slope, aspect, elevation and geologic substrate at each site. Measurements of soil texture, pH, and electrical conductivity were taken for a representative subsample. A map of the vegetation of the Park was made by relating the sample points to their corresponding spectral signatures on vertical aerial photographs and locating boundaries between vegetation units by means of changes in photo signatures.
Vegetation in these arid to semi-arid environments appears to be strongly related to particular combinations of regolith thickness, bedrock composition and depth to water table. Elevation and slope exposure control vegetation patterns to a much smaller extent. Vegetational units are distinct, and can be readily visualized. The six units mapped, in order of relative importance, (area covered) were: blackbrush, juniper-pinyon woodlands, semi-desert grasslands, sagebrush-fourwing saltbush shrublands, salt-desert shrublands and riparian tall shrublands. These vegetational units are related to specific combinations of environmental factors. Boundaries between units are sharp vegetationally and environmentally. Moisture availability appears to be the key factor, but effective soil moisture is largely controlled by regolith/bedrock relationships.
Grasslands predominate at all elevations where regolith is over 50 cm in thickness and there is no access of plant roots to the water table. Regolith that is uniformly thinner than 50 cm supports vegetation dominated by blackbrush (Coleogyne ramosissima). Sandy areas that provide immediate root access to the water table support thickets of Salix, Tamarix, and other riparian shrubs. Shrublands dominated by Atrinlex canescens and Artemisia tridentata occur on thicker sand deposits with seasonal root access to capillary water. Where competent bedrock is exposed and joints are developed, Pinus edulis, Juniperus osteosperroa and various upland shrubs dominate. Several species of Atrinlex dominate the salt-desert shrublands where clayey shales crop out.
Historical grazing use by domestic livestock has altered the composition and cover in grasslands, chiefly in the southern part of the Park. Elsewhere, grassland modification is slight because of more difficult access. other vegetation types have experienced less obvious changes.
The many abandoned roads within the Park date chiefly from extensive mineral exploration in the early 1950's. Secondary succession on these disturbed areas is extremely slow.
Loope, Walter Lee, "Relationships of Vegetation to Environment in Canyonlands National Park" (1977). All Graduate Theses and Dissertations. Paper 2110.
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