Graduate Thesis Or Dissertation
 

Habitat relationships of birds and young-growth Douglas-fir in northwestern California

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ns0647979

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  • Ninety-one species of birds were surveyed in grass/forb, early and late shrub/sapling, pole, and medium sawtimber stages of young-growth Douglas-fir in northwestern California; patterns of bird distribution and abundance were related to habitat conditions and even-age silvicultural treatments. Seven species (band-tailed pigeon, western wood pewee, dusky flycatcher, western bluebird, fox sparrow, purple finch, and evening grosbeak) have probably increased in population size or distribution since extensive clearcutting in the study area began in the early 1950's. Six species (Hammond's flycatcher, chestnut-backed chickadee, red-breasted nuthatch, brown creeper, golden-crowned kinglet, and hermit warbler) are restricted to forest stages and probably have decreased in population size or distribution. Abundances of various species were associated with presence of a forest overstory, hardwood stem density, deciduous foliage volume, height and patchiness of shrub cover, number plant species, and snag density. Slope angle and distance to permanent water or to the next nearest similar habitat type explained some variation in abundance of a few species. The grass/forb stage had the lowest number of bird species and lowest total density, while the late shrub/sapling stage had the highest; species composition varied markedly across the young-growth stages. Cluster analysis defined Shrub stage specialists and forest stage Specialists. Seasonal patterns of permanent resident species suggested that the shrub stage specialists are most limited in distribution during winter, and that their winter distributions may reflect optimal ("source") habitat. In contrast, forest stage specialists showed no seasonal changes of distribution, or were more restricted in distribution during the breeding season. All phases of the clearcutting system, including site preparation, stocking control, intermediate treatments, and final harvest, greatly affect stand conditions. No one stand condition, young-growth stage, or silvicultural treatment provided best habitat for all bird species. Simplification of forest stand structure by reduction or elimination of hardwoods, snags, and large diameter softwoods, could lead to low within-stand but high between-stand diversity of vegetation and bird assemblages. Even-age silvicultural systems, however, can integrate management objectives for timber production and bird habitat.
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