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.

Water potential, leaf conductance, growth, nitrogen content, and seedling survival of Wyoming Big Sagebrush (Artemisia tridentata ssp. wyomingensis) following defoliation of the herbaceous understory were assessed during two growing seasons. Precipitation was 107% and 63% of the long-term mean (283 mm) in 1989 and 1990, respectively, which presented an opportunity to study impacts during a drought and a non-drought year. Response of Artemisia was measured on a site seeded to Agropyron desertorum in the late 1960s, and a native site with Stipa thurberiana, Festuca idahoensis and Poa sandbergii in the understory. The two sites were analyzed as separate experiments. The dry year had a significant effect on plant water relations and growth of Artemisia on both sites. Pre-dawn water potentials averaged 1.23 MPa more negative on the seeded site and 1.22 MPa more negative on the native site in 1990 compared to the previous year. Mid-day water potential averaged 1.22 MPa more negative on the seeded site and 1.13 MPa more negative on the native site in 1990 compared to 1989. Morning leaf conductance in 1990 was 61% lower on the seeded site and 51% lower on the native site than in 1989. Mean afternoon leaf conductance in the drought year was 62% less on the seeded site and 63% less on the native site. Nitrogen content in current year's growth was reduced 29% on the seeded site and 18% on the native site from 1989 to 1990. Vegetative and reproductive shoot (stem plus leaves) weights were reduced by over 80% in 1990 compared to 1989. Other production variables showed similar reductions in the drought year. Nitrogen content was 11% greater in current year's growth from shrubs on control as opposed to defoliated plots on the native site in 1989. Shrubs on control plots had 8% heavier reproductive stems per unit of canopy, and 7% longer vegetative stems than shrubs on defoliated plots in 1989 on the seeded site. Shrubs on control plots had 18% fewer annual leaves per unit of vegetative shoot, but 12% more primary ephemeral leaves per vegetative shoot than shrubs on defoliated plots in 1990 on the seeded site. In 1990, shrubs on control plots on the seeded site had 11% more ephemeral leaves per vegetative shoot while shrubs on the control plots on the native site had 8% fewer ephemeral leaves per vegetative shoot. Large shrubs generally had more and heavier leaves, and longer and heavier stems than medium shrubs. Exceptions included large shrub lateral stems were 30% shorter than those of medium shrubs, and large shrubs had 37% fewer annual leaves per vegetative shoot than medium shrubs in 1989 on the seeded site. Drought had substantial negative impact on water relations and growth of Wyoming big sagebrush, while defoliation of understory vegetation had little effect. / Graduation date: 1993

Thesis (M.App.Sc.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2001. / Bibliography: leaves 308-333.

Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 23, 2010). Includes bibliographical references.

Thesis (Ph. D.)--University of Arizona, 1998. / Includes bibliographical references (p. 178-190).

Graduation date: 2003

Thesis (M.S.)--Boise State University, 2009. / Includes abstract. Includes bibliographical references (leaves 81-91).

Thesis (Ph.D.)--University of Adelaide, Dept. of Environmental Biology, 2002. / Accompanying CD-ROM inside back cover, includes Appendices. Bibliography: leaves 242-266.

Habilitationsschrift--Universität Münster with title: Die Wanderviehwirtschaft in den Hochgebirgs- und Beckenlandschaften der westlichen USA und ihre Auswirkungen im Naturraum. / Includes English summary. Includes bibliographical references (p. 419-469).

Thesis (M.S.)--Boise State University, 2009. / Title from t.p. of PDF file (viewed Mar. 29, 2010). Includes abstract. Includes bibliographical references (leaves 81-91).