Structure retention is a practice used in managed forests to assist the conservation of biological diversity, whereby green trees, dead trees (i.e., snags), and downed wood are retained during timber harvest. This activity is recognized as beneficial; however, there is little scientific support to guide the management prescriptions (e.g., density, patch sizes, distribution pattern). I quantified wildlife responses to structure retention attributes in harvest units across 4 regions in the Pacific Northwest, USA, during the summers of 2008-2010. These 4 regions encapsulated ecological and management variability of intensively managed forests ranging from Washington to northern California. Bird species were observed at retention sites across the 4 regions and white-headed woodpeckers (Picoides albolarvatus) were studied more intensively in California. I used a hierarchical modeling framework to separately model the processes related to data collection (e.g., detection probability) from those related to the state variables of interest (e.g., species occupancy). This framework allowed for the examination of factors which influenced each process. The results provide empirical support for management strategies that can improve the effectiveness of structure retention for addressing biodiversity objectives.In the first chapter, I report on a multi-species occurrence model which estimated occupancy and detection probabilities for all bird species observed at retention sites. Retained tree count was associated with an increased occupancy probability for 70% of the observed species. The community response to tree count was consistent across all study areas and years - species richness estimates increased with tree count and approximated a species-area curve. Distance to nearest mature forest did not significantly affect occupancy probability for any observed species, and therefore, had no significant relationship with species richness. These results suggest that the diversity of birds using structure retention in harvest units can be maximized at patches of >10-15 rotation age trees.In the second chapter, I used a multistate site occupancy model to estimate the probabilities of occupancy and nesting for white-headed woodpeckers in harvest units where structure retention was present. Snag density had a significant positive association with nesting probability. Mature forest proportion was negatively associated with nesting probability, though there was considerable uncertainty. High occupancy (0.98) and nesting (0.89) probabilities suggest that current structure retention policies have provided the necessary habitat conditions for white-headed woodpecker nesting in harvest units of northern California. Forest managers can maximize nesting probability by retaining >2 snags/ha during harvest.In the third chapter, I examined reproductive success for white-headed woodpeckers using models of nest survival and number of young fledged. We documented a high nest success rate (0.85) and found that successful nests were most likely to produce >=3 young. None of the habitat variables that were examined at multiple scales were able to significantly describe variation in either metric of reproductive success. Current forest management practices in northern California appear to be providing habitat conditions that are conducive to the species' persistence in this region.
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