Woodland reduction and long-term change in breeding bird communities

Forested ecosystems in the western United States have been the focus of tree reduction efforts for decades, with the intent of improving forage for livestock and wildlife. Yet, the long-term consequences of tree removal for biodiversity are virtually unknown. We conducted bird and vegetation surveys in northwestern Colorado where trees were mechanically removed over 40 years ago. We evaluated differences in avian species richness and community composition, and used a Bayesian hierarchical approach to determine if tree removal had long-term effects on bird density. We found that tree reduction initiates a long-term change from dense pinyon (Pinus edulis)-juniper (Juniperus osteosperma) woodlands to sagebrush scrub, fundamentally altering bird community composition. Disturbed sites were used by fewer species and largely dominated by shrubland-obligate birds. Further, bird densities were markedly different between historically disturbed sites and reference sites. Densities of many species were correlated with specific vegetative characteristics (e.g., mean tree diameter) that could be factored into management decisions to better sustain diverse natural communities. (c) 2016 The Wildlife Society. We evaluated differences in bird species richness and density between pinyon-juniper woodland reference sites and those that were mechanically disturbed over 40 years ago. We found that historical tree removal catalyzed a long-term change from dense pinyon-juniper forests to sagebrush scrub, fundamentally altering breeding bird communities.