Date of Award:

1988

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Ecology

Department name when degree awarded

Range Science

Advisor/Chair:

Philip J. Urness

Abstract

Three experiments were conducted to assess the potential for using Spanish goats to manage Gambel oakbrush winter range, dominated by Gambel oak (Quercus gambelii), for mule deer (Odocoileus hemionus). Summer- time food selection of goats, effects on plant community composition, and consequent effects on mule deer nutrition and foraging behavior were examined.

An apparent preference for juvenile oak browse, and low use of oak twigs was observed. Selection for juvenile browse may have been facilitated by the retarded phenology of oak as compared to that of associated flora. This differential was maintained by repeated browsing. Animal performance, reflected in mass-specific gain rates, varied markedly. However, poor performance when observed, was not correlated with high juvenile oak content in diets.

Goat browsing did not affect density of any shrub species. Stem size distributions changed in browsed oak populations only; skewness of these increased over time because of sprouting. Sprout weights increased in browsed oak populations, but declined in comparably browsed serviceberry (Amelanchier alnifolia) populations. The only other significant sprout response was a numerical increase in browsed snowberry (Symphoricarpos oreophilus) populations. Relationships between stem size and stem productivity in heavily browsed oak and serviceberry were characterized by lower slopes than those for adjacent control populations. Conversely, relationships in rabbitbrush (Chrvsothamnus viscidiflorus) populations, which were little used, were characterized by higher slopes than those for adjacent control populations. Sagebrush (Artemisia tridentata wvominqensis) production also responded positively, but via increased intercept. Browsing reduced productivity of both serviceberry and oak, but enhanced that of sagebrush. A positive production response was suggested for herbaceous species.

Forage-base changes induced by goats caused wintering deer to increase the proportion of sagebrush in their diets under snow-covered conditions but not under snow-free conditions. Under snow-covered conditions, deer using goat-browsed pastures consumed diets higher in dry matter digestibility, but not protein, than those consumed by deer in control pastures. Dietary quality was unaffected by prior goat browsing under snow- free conditions. Furthermore, quality of diets consumed under snow-free conditions was not better than that consumed under snow-covered conditions.

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