Avian communities in relation to habitat influenced by fire in a sagebrush steppe landscape Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9593tx185

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  • Fire suppression in high-elevation sagebrush steppe over the last century has profoundly influenced the structure and complexity of vegetation communities. Although fire is the primary management tool used to restore these areas, the impact of this management practice on associated avian communities is poorly understood. We examined patterns of habitat use by breeding birds one year after a prescribed burn on Steens Mountain in southeastern Oregon. During the 2000 breeding season, we determined bird distribution and abundance using a fixed-radius point count method at 205 sites representing burned and unburned sagebrush, juniper, and aspen habitats. We developed resource selection models for individual species breeding in the sagebrush steppe, and predictive models of bird species richness and diversity (H') by combining bird and local vegetation data collected at the field sites with remotely sensed landscape data. We used Akaike's Information Criterion (AICC) to select the best-approximating model from a suite of a priori candidate models. Brewer's sparrows, sage thrashers, and green-tailed towhees had a positive relationship with increasing area of sagebrush, whereas vesper sparrows were negatively associated with area of sagebrush. Green-tailed towhee occurrence initially increased with increasing juniper within I km, but eventually declined as juniper continued to increase. All other species showed a strong negative relationship with increasing juniper. Brewer's sparrows, sage thrashers, and green-tailed towhees were also sensitive to sagebrush abundance within 1 km. Bird species richness and diversity (Ht) were positively associated with increasing area of aspen and juniper density at the site. However, both bird community measures quickly reached a threshold at low values of either habitat type. Bird species richness increased with increasing habitat diversity (Ht) within 1 km, while bird diversity (Ht) increased with increasing habitat richness at the site. The prescribed fire minimally impacted critical aspen habitat. Furthermore. our models indicate that even small aspen stands and the presence of a few juniper trees are adequate to sustain avian diversity in this landscape. These results suggest that, although fire has an immediate impact on some birds breeding in sagebrush steppe, in the long term, periodic fire enhances avian diversity and creates suitable habitat conditions for sagebrush obligates by maintaining aspen stands and limiting juniper.
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