Graduate Thesis Or Dissertation
 

Small mammal relationships with downed wood and antelope bitterbrush in ponderosa pine forests of central Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/tm70mz116

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  • Downed wood and antelope bitterbrush (Purshia tridentata) are often managed on federal ponderosa pine (Pinus ponderosa) forests in central Oregon to prevent catastrophic wildfires and provide wildlife habitat. However, although much is known regarding the roles of downed wood and bitterbrush in wildfire behavior, little is known regarding the relationships of small mammal populations with downed wood and bitterbrush in these pine forests east of the Cascade crest. This study had four primary objectives: 1) to test for differences in population parameters (i.e., density, reproductive condition, and survival) of common small mammals between forested areas with high and low downed wood volumes; 2) to test for differences in these small mammal population parameters between forested areas with high and low shrub cover; 3) to quantify relationships of small mammal population parameters with different habitat features, emphasizing downed wood volume bitterbrush cover, and total shrub cover and 4) to quantify relationships between small mammal population parameters and habitat features across seasons and years to assess temporal variability. Study units representing five replicates of three combinations of shrub cover and downed wood volume (high shrub cover/high downed wood volume, high shrub cover/low downed wood volume, low shrub cover/low downed wood volume) were selected in the Deschutes National Forest east of the crest of the Cascades Mountains in central Oregon. A total of 2,654 small mammals representing nine species were captured in live traps on the 15 study units during four sampling periods: early summer 2000 (June 25 to July 27), late summer 2000 (August 29 to September 30), fall 2000 (October 2 to October 28), and early summer 2001 (July 3 to August 4). Yellow-pine chipmunks (Tamias amoenus), golden-mantled ground squirrels (Spermophihis lateralis), and deer mice (Peromyscus maniculatus) comprised 98% of the captures. Golden-mantled ground squirrel survival and density were significantly higher on study units with high versus low downed wood volume. Yellow-pine chipmunk populations did not exhibit significant relationships with downed wood volume, but chipmunk density was higher on study units with high versus low shrub cover. Deer mouse populations failed to exhibit significant relationships with downed wood volume or shrub cover. For the three small mammal species, there was considerable variation among seasons, years, and locations for many of the population parameters examined. Results from this study suggest that managing downed wood and antelope bitterbrush in ponderosa pine forests of central Oregon may affect the small mammal community through changes in density and survival of golden-mantled ground squirrels and yellow-pine chipmunks. Such impacts on the small mammal community will, consequently, influence other aspects of forest ecology including fire behavior and shrub regeneration due to the consumption and dispersal of bitterbrush seeds by these chipmunks and ground squirrels.
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