Date of Award:

5-1987

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Department name when degree awarded

Range Science

Committee Chair(s)

Brien E. Norton

Committee

Brien E. Norton

Committee

Jim Richards

Committee

Fred Provenza

Committee

David Turner

Committee

Neil West

Abstract

Patterns of grazing on individual crested wheatgrass plants were studied using scale maps of plant basal outlines within randomly located plots. The occurrence and extent (part of plant grazed, stubble height) of grazing on each plant was recorded on the maps at two and three day intervals throughout a grazing treatment. Allometric equations for estimating phytomass from plant photosynthetic volume were generated using nonlinear regression analysis. Equations were specific to year. The percent weight remaining in the stubble of a grazed plant was estimated using a second-order polynomial equation relating cumulative percent plant height to cumulative percent plant weight. A modified bootstrap analysis was used due to the autocorrelated nature of these data. These equations were used to estimate the percent biomass grazed from individual plants.

The presence of standing dead culms substantially reduced the severity of grazing on individual crested wheatgrass plants. This effect was most pronounced for large plants. The deterrence effect of standing dead culms declined as plants matured, but remained an important factor affecting grazing severity. The pattern of grazing on crested wheatgrass plants was examined under three grazing systems: 1) continuous season-long grazing (CSLG), 2) high intensity grazing (approximately 60 percent utilization in eight days), and 3) short duration grazing. For all grazing treatments, a lower proportion of small plants was grazed than medium and large. Only under CSLG were small plants grazed more severely than large plants. Under all ocher grazing treatments, medium and large plants were grazed as severely as small plants.

The proportion of plants regrazed was low when grazing began at the boot phenological stage and regrowth was minimal. It was higher when grazing began at later phenological stages, presumably due to the presence of regrowth. The proportion of small grazed plants that were regrazed was much lower than the proportion of large grazed plants that were regrazed. The regrazing event, however, involved, on average, more of the previously ungrazed portion of a plant than the part which had been grazed before. These results indicate that grazing of regrowth on crested wheatgrass pastures under CSLG may not be a serious problem.

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