Date of Award:

1978

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Advisor/Chair:

Brien E. Norton

Abstract

A study was conducted on pastures grazed by sheep in late winter at the Desert Experimental Range in southwest Utah. Estimates of plant cover and herbage production were obtained in 1977 and used to examine longterm trends in the vegetation.

The nutritional value of the six most important species of the area was assessed by chemical analysis. In addition, a management strategy was developed for obtaining some utilization of the range during the spring and summer months without affecting the traditional winter use by sheep.

Long-term records (since 1937) in cover suggest a modest increase in grasses and a decrease in shrub cover. But there are insufficient data to infer range condition and trend. Long-term herbage production data (since 1938) show a substantial increase in annual species over the last twenty years. The year-to-year variability is very high, apparently depending on the prevailing climate conditions. Grass production was less variable than shrub production.

No significant difference (P<.05) in crude protein content was found between shrubs and grasses from April to September, which contrasts with the later decline in nutritive value of grasses during the winter. Phosphorus content was significantly higher in shrubs than in grasses, but the high lignin content of shrub forage made its digestibility significantly lower than for grasses.

Based on the nutritional analysis of forage and long-term records of climate and plant production, a management strategy was devised to make more efficient use of the salt-desert shrub vegetation. Climatic conditions will favor good forage production about four years out of ten. Perennial grasses, annuals, and winterfat (Ceratoides lanata) showed better response to favorable climatic conditions than the other species. It is proposed in this study that, in these years of high production, the range could be used by cattle in the spring or summer, and thereby al low occasional resting of mountain summer pastures. Such opportunistic summer grazing on the desert should not be detrimental to winter sheep grazing, but the plan would need to be field-tested on an experimental or trial basis to evaluate ecological responses to increased livestock use.

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