Associations Between Avian Spruce-fir Species, Harvest Treatments, Vegetation, and Edges

Habitat loss is the primary cause of species loss and declines of global biodiversity. Several birds associated with the spruce-fir forest type (hereafter spruce-fir birds) have declining populations across the continent in the Atlantic Northern Forest, and the extent of coniferous forest has declined in some areas. This region is extensively and intensively managed for timber products. To investigate the influence from harvest treatments on the spruce-fir bird assemblage during the breeding and post-breeding period in lowland conifer and mixed-wood forests, we used avian point count detection data to test for associations between avian assemblages and seven common harvest treatments. Spruce-fir avian assemblages had greatest abundance in regenerating clearcuts combined with postharvest treatments (i.e., herbicide and precommercial thinning), and within stands having ≥60% spruce-fir tree composition. Richness of spruce-fir avian assemblages were greatest in stands with immature trees and greater spruce-fir tree composition, and clearcuts combined with postharvest treatments had greater spruce-fir tree composition compared to other treatments. Next, we tested for effects from management, years-since-harvest, and vegetation on abundance of 19 conifer associated avian focal species while accounting for the effects from detection probability. Abundance of six species differed significantly among harvest treatments, and one species was associated with years-since-harvest, indicating that management treatments provided important information. In addition, fourteen species had significant associations between abundance and vegetation variables, suggesting that managers could target specific vegetative outcomes when managing for focal species. We tested for differences in avian abundance and richness at stand interior ≥80 m from edges, low-contrast edges at the junction of two regenerating stands, and high-contrast road edges with managed buffers using a novel multi-species abundance model. Spruce-fir birds had greater richness at stand interior compared to high-contrast edge, and stand interior had greater spruce-fir tree composition compared to high-contrast edge, while low-contrast edge was intermediate. Road edges reduced habitat for spruce-fir birds. Combined our results suggest that management could promote habitat for spruce-fir birds through: 1) application of postharvest treatments such as herbicide and precommercial thinning; 2) using management that targets focal species by using outcome-based silviculture; 3) minimizing access road edges and roadside buffers