Effects of goat browsing on gambel oak communities in northern Utah.

Abstract

Replicated populations of 5 shrub species were monitored over a 3-year period to assess community responses to intensive browsing by Spanish-type goats. Response variables included stem density, stem-size distribution skewness, stem diameter-stem production relations, and sprout abundance and weight. No species exhibited a density change. Size distribution skewness increased only in browsed oak (Quercus gambelii Nutt.) populations. Sprout weights also increased in browsed oak populations, but declined in comparably browsed serviceberry (Amelanchier alnifolia Nutt.) populations. The only other significant sprouting response was an increase in sprout numbers in browsed snowberry (Symphoricarpos oreophilus Gray) populations. Relationships between basal stem diameter and stem production of 4 species were altered by goat use. The slopes of these relations were consistently lower in browsed populations of oak and serviceberry than in adjacent control populations, indicating that browsing reduced productivity, especially of large stems. Conversely, slopes of rabbit-brush (Chrysothamnus viscidiflorus lanceolatus (Hook.) Nutt.) relations increased in goat-browsed pastures relative to those of control populations; rabbitbrush was avoided by goats. Similarly, big sagebrush (Artemisia tridentata wyomingensis Nutt.) was avoided and its stem production responded positively in communities subjected to goat browsing. Important cumulative effects of goat browsing included declines in productivity of serviceberry and oak, and an increase in that of sagebrush.