Herbaceous and avifauna responses to prescribed fire and grazing timing in a high-elevation sagebrush ecosystem
Date
2011
Authors
Erickson, Heidi Jo, author
Aldridge, Cameron L., advisor
Hobbs, N. Thompson, advisor
Detling, J. K. (James K.), committee member
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Abstract
Changes in land use over the last two centuries have been linked to reduced geographic distributions of sagebrush (Artemisia spp.) habitats and sagebrush associated avifauna. Livestock grazing is one of the principle land uses of publicly administered sagebrush ecosystems. Prescribed fire and other sagebrush control methods are often implemented in an attempt to increase the quantity or quality of available livestock forage. These treatments have also been recommended by some as a tool for enhancing habitat to meet seasonal forage requirements for greater sage-grouse (Centrocercus urophasianus) or other wildlife species. In this thesis, I examine differences in: 1) herbaceous productivity (peak standing crop biomass), 2) relative habitat use by sage-grouse, and 3) habitat suitability for migratory songbirds related to prescribed fire and summer grazing timing treatments in a high-elevation sagebrush community. Increased livestock forage availability in burns occurred only during one of three post-burn years investigated and was further limited to only one of three grazing treatment pastures (early summer). Graminoid peak standing crop in burn treatments with later summer grazing never surpassed unburned big sagebrush plots subjected to the same grazing treatment. Habitat suitability and use by avian species appeared to be largely unaffected by post-fire grazing timing. Although sage-grouse use of burn treatments was greater when burn configuration was more heterogeneous, use was minimal across all burn treatments the first four years after burning. Sagebrush obligate songbirds, such as Brewer's sparrow (Spizella breweri) and sage thrasher (Oreoscoptes montanus), also strongly avoided burn treatments, particularly with increasing distance to intact big sagebrush (A. tridentata) nesting substrate. Although ground nesting species, such as vesper sparrow (Pooecetes gramineus), preferred reduced shrub cover associated with burn treatments, this species also responded negatively to more uniform patterns of big sagebrush removal. These results suggest that avian species are minimally impacted by summer livestock grazing at the light to moderate intensity levels resulting from my grazing treatments, regardless of timing. However, sage-grouse and migratory songbirds displayed clear seasonal avoidance of burn treatments. These results demonstrate that negative avifauna responses to sagebrush removal may strongly outweigh limited short-term gains in livestock forage production resulting from prescribed fire in some high-elevation big sagebrush systems.
Description
Rights Access
Subject
sage thrasher
grazing timing
prescribed fire
sagebrush
sage-grouse
Brewer's sparrow