Small mammal and bird abundance in relation to post-fire habitat succession in mountain big sagebrush (Artemisia tridentata ssp. vaseyana) communities

Graduation date: 2011Access restricted to the OSU Community at author's request from Dec. 22, 2010 - Dec. 22, 2011.Fire is an important disturbance mechanism in big sagebrush (Artemisia\ud tridentata) communities, yet little is known about wildlife population dynamics during\ud post-fire habitat succession. I estimated the abundance of small mammals and birds in\ud relation to fire history in mountain big sagebrush (A.t. spp. vaseyana) communities on the\ud Sheldon National Wildlife Refuge in the northwestern Great Basin, USA. I employed a\ud chronosequence approach that took advantage of multiple wildfires that had occurred in\ud similar plant communities between 7 to 20 years prior to sampling.\ud Belding’s ground squirrel (Spermophilus beldingii) were approximately 10 times\ud as abundant in burned areas relative to adjacent unburned habitat regardless of the\ud number of years since a burn occurred. Deer mouse (Peromyscus maniculatus) was more\ud abundant on more recently burned sites, but not at sites closer to full vegetation recovery.\ud Great basin pocket mouse (Perognathus parvus), sagebrush vole (Lemmiscus curtatus),\ud and least chipmunk (Tamius minimus) abundance did not vary as a function of fire\ud history, but some variance was explained by habitat features such as rocky areas and the\ud canopy characteristics of sagebrush.\ud Bird diversity was higher in unburned habitats irrespective of the number of years\ud of recovery out to 20 years. Nine of the 12 most widely occurring species of birds in the\ud study have population densities influenced by fire or post-fire habitat succession to at\ud least 13 to 20 years following a burn. Sage Sparrow (Amphispiza belli), Black-throated\ud Sparrow (Amphispiza bilineata), and Spotted Towhee (Pipilo maculatus) occurred at\ud relatively low densities and were nearly restricted to unburned habitats. Green-tailed\ud Towhee (Pipilo Chlorurus), Gray Flycatcher (Empidonax wrightii), American Robin\ud (Turdus migratorius), and Brown-headed Cowbird (Molothus ater) occurred at lower\ud densities in burned areas than adjacent unburned areas although the relationship was not\ud strong for the latter two species. The magnitude of the difference in density between\ud burned and unburned sites within a landscape diminished with the number of years of\ud vegetation recovery for Green-tailed Towhee. Brewer’s Sparrow (Spizella brewerii)\ud occurred at lower densities relative to adjacent habitat in the most recent burn, but\ud occurred at higher densities after 20 years of habitat succession, suggesting a positive\ud response with a multiple decade lag period. Horned Lark (Eremophila alpestris) and\ud Vesper Sparrow (Pooecetes gramineus) respond positively to fire, but densities were\ud similar to unburned areas after 20 years of habitat succession.\ud An ordination analysis captured 86% of the variation in 12 bird species with 3\ud orthogonal axes. My research demonstrates that strong community structure exists for\ud birds associated with mountain big sagebrush habitats, and that fire influences\ud community structure for multiple decades