Bird communities in 5- to 34- year old managed Douglas-fir stands on the Willamette National Forest, Oregon Cascades Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/7p88cm77s

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  • Breeding bird communities were examined in 18 managed Douglas-fir stands in 6 age classes from 5 to 34 years old in spring and early summer, 1993 on the Detroit Ranger District, Willamette National Forest, Oregon. The range of seral stages included early shrub/sapling, late shrub/sapling, and pole. In general, the 9 younger stands were opencanopy while the 9 older stands were closed-canopy. Of the 50 bird species recorded, 21 had large enough sample sizes for analysis. Of these 21, 8 showed a pattern of increasing abundance with increasing stand age (chestnut-backed chickadee, golden-crowned kinglet, hermit thrush, hermit warbler, Pacific-slope flycatcher, Swainson's thrush, Wilson's warbler, winter wren). Six species showed a pattern of decreasing abundance with increasing stand age (American robin, darkeyed junco, rufous hummingbird, white-crowned sparrow) and 4 species peaked in abundance in age class 2 (10 - 14 years old) before decreasing with increasing stand age (dusky flycatcher, MacGillivray's warbler, orange-crowned warbler, rufous-sided towhee). Two species did not exhibit any particular pattern associated with stand age (warbling vireo, western tanager). Three species were dropped from analysis because their average territory size is larger than the smallest stand surveyed. Abundance indices for species which showed an increasing pattern were positively associated with habitat variables describing conifer basal area, percent cover of live conifer crown between 4 m and the height of the tallest conifer tree, number of conifer stems/ha between 20- and 30- cm dbh, and/or percent cover of live hardwood crown between 4 m and the height of the tallest hardwood tree. Abundance indices for species which showed a decreasing or peaked abundance were negatively associated with the same variables, excluding percent cover of hardwood crown. Total abundance, species richness, and species diversity did not differ (P<0.05) among the age classes. However, bird community composition changed with increasing stand age. Open-canopy stands were dominated by species preferring open-canopy habitats (top 5 species in order of abundance: dark-eyed junco, MacGillivray's warbler, rufous hummingbird, dusky flycatcher, rufous-sided towhee) while closed canopy-stands were dominated by species preferring closed-canopy habitats, (hermit warbler, dark-eyed junco, chestnut-backed chickadee, golden-crowned kinglet, Swainson's thrush); the dark-eyed junco was an exception. The rate of bird community change was rapid along the gradient of open-canopy stands but appeared to reach a plateau once canopy closure was reached.
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