Community structure and niche characteristics of upland and lowland western boreal birds at multiple spatial scales

Abstract

Direct and indirect effects of disturbance may cause the decline of specialist species and alter the condition of ecological communities. We characterized the community structure and niche characteristics (niche position, marginality, breadth) of upland and lowland boreal birds at scales relevant to both natural and human disturbance patterns in western boreal forests undergoing rapid and extensive multi-sector resource development. Our goal was to identify the degree of ecological specialization in order to inform activities directed at conserving a diversity of species (e.g. specialists and generalists) within the western boreal bird community. We used avian data (>5,220 point counts) and environmental variable data comprised of forest composition, stand, and landscape pattern metrics at local (7.1ha), landscape (1,963ha), and regional (11,310ha) scales to determine boreal bird distribution and community-level associations using Canonical Correspondence Analysis (CCA) and Outlying Mean Index (OMI) analysis. OMI analysis explained a high proportion of variance in the dataset (71.8%) and separated boreal birds along two axes associated with moisture–productivity and age–structural complexity gradients. Niche position was influenced by local scale variables (height, age, area of mature-old forest, area of wet soil types), but also landscape and regional scale variables (total area of hardwood and conifer, mean nearest neighbour distance of conifer, and total core area of productive upland conifer). Only 15 of 67 species (22%) had marginal (atypical) niches and narrow niche breadths exhibiting specialization in old hardwood and white spruce forests and burned, open, and lowland habitats. Most species occupied typical or common habitats within the study area and exhibited generalist strategies typical of species in heterogeneous and disturbed habitats that undergo frequent change. Our results suggest the need to design and implement multi-species plans to conserve a diversity of western boreal bird species (e.g. specialists and generalists) at the regional scale.