Bird species exhibit a wide range of responses to thinning treatments depending on logging intensity, time since harvest, forest type, and study area. Broad-scale disturbances such as logging and spruce beetle outbreaks cause considerable change to subalpine forest habitat. Our objective was to determine if bird diversity was significantly different in logged versus unlogged Engelmann spruce-subalpine fir forests. We conducted breeding bird censuses at high elevations in the San Juan National Forest of Colorado for four years from 2013-2016. In 2015, 18 out of 54 plots became infested with spruce bark beetles, which allowed us to investigate relationships between community-level occupancy, selective logging, early stages of spruce beetle infestation, and forest structure data collected over the four years. We used a community-level, multi-species occupancy model to analyze the effect of logging and other habitat features on species occupancy and richness at our sites.
We did not find any evidence of changes in avian species richness between sites as a result of selective thinning. In contrast, we found statistically supported occupancy relationships with the number of beetle-infested trees, the number of snags, quadratic mean diameter of all standing trees, and shrub cover. Spruce-fir forests are extensively managed for resource output and to maximize resistance to ecological disturbances such as fire and bark beetle outbreaks. Our research is the first to quantify the effects of thinning treatments on breeding birds in spruce-fir forests – the most important and extensive forest type in Colorado. We provide evidence that limited amounts of selective harvesting is not likely to impact the bird community in the long term - an important contribution for assessing the impacts of forest management strategies on a key ecosystem service of spruce-fir forests.