Bird communities in managed conifer stands in the Oregon Cascades : habitat associations and nest predation

Graduation date: 1994Green-tree retention is being implemented on state and\ud federal lands in Oregon. Silvicultural prescriptions with\ud tree and snag retention are thought to mimic natural\ud disturbance patterns in the Pacific Northwest more closely\ud than traditional silvicultural practices, which reduce\ud structural complexity. The effects of green-tree retention\ud on native bird species in the Pacific Northwest are largely\ud unknown. Consequently, this study examined avian\ud communities, individual species abundances, habitat\ud associations, and artificial nest predation in the West-central\ud Oregon Cascade Range. Between May and August 1992,\ud 4 clearcut, 4 green-tree retention, and 4 mature conifer\ud stands were studied. Species diversity was greater in\ud mature stands than in clearcuts. Total bird abundance and species richness did not differ among stand types, but\ud community composition did. Differences in community\ud composition were related to differences in vegetation\ud structure and composition. Species showed individualistic\ud responses to stand types, and individual species abundances\ud were correlated with conifer and snag densities more than\ud with other variables. Green-tree retention stands provided\ud habitat for some birds that are associated with early- and\ud late-seral habitats. Predation on ground nests was greater\ud in clearcuts than retention stands. Shrub nest predation\ud was greater in retention stands than in clearcuts or mature\ud stands. These results support the hypothesis that trees\ud and snags which are retained in harvest units serve as\ud perches which facilitate the location of shrub nests by\ud predators. Retention stands may be sink habitats for\ud species which nest in them unsuccessfully. Open canopy\ud species which are negatively associated with green-tree\ud retention may show further declines in population if green-tree\ud retention stands replace clearcuts on state and\ud federal lands in Oregon. In order to provide habitat for\ud native species, a variety of stand conditions should be\ud maintained across the landscape and management objectives\ud should be tailored to individual species or communities