A Guild-Based Assessment of the Impacts of Silvicultural Practices on Songbird Biodiversity

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Marlyse Duguid
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Songbirds are irreplaceable members of their ecosystems and valuable indicators of ecological health, yet populations have been declining in recent years, particularly in the eastern United States. Bird count surveys were conducted annually in Marsh-Billings-Rockefeller National Historical Park’s 550 acres of forest in Woodstock, Vermont from 2006 to 2018 to evaluate the overall trends in avian populations and the impact that forest structure variables have upon specific songbird response guilds. Bird richness levels were found to have decreased linearly by 30% over these years (p = 0.007), and were significantly higher on average in mosaiced forests (mean = 8.633) than late successional forests (mean = 7.135). Specific response guilds were then evaluated, and both canopy nesters and shrub nesters were found to be nearing concerning levels in accordance with the National Park Service avian ecological integrity thresholds which specify the species richness levels that should be seen within each guild. Forest variables that can be selected for through silvicultural strategies were found to significantly correlate with the changes in total richness for these guilds over time. For canopy nesters, these characteristics were basal area per square meter (p = 0.010) and percent basal area of dominant canopy species (p = 0.033), and for shrub nesters the significant variables were regenerating seedling density (p = 0.001), regenerating sapling density (p = 0.038), and coarse woody debris volume (p = 0.031). The results of these analyses prompted management recommendations, including increasing basal area per hectare of dominant species and increasing overall forest heterogeneity. This paper evaluates the complex relationship between forests and birds to understand how to maintain the healthiest and most diverse community of birds within the park through the careful manipulation of forest characteristics.