The influence of habitat diversity and structure on bird use of riparian buffer strips in coastal forests of British Columbia, Canada

I investigated the role of habitat structure in explaining bird species richness and abundance in riparian buffer strips of old-growth coniferous forest on western Vancouver Island, British Columbia. Using buffer strips of varying widths and a control from undisturbed riparian forest, I tested the hypothesis that vegetation differs in buffer strips of varying width. I selected 10 summary variables to represent broad-scale vegetation attributes of riparian habitat. Deciduous tree density was higher, and shrub richness was lower in wide buffers compared with narrow buffers. I then used Akaike information criterion to examine whether vegetation structure or buffer width best explained patterns of bird richness and abundance in riparian habitats. Species richness and abundance in several foraging guilds were explained better by buffer width than by vegetation. Abundances of three bird habitat guilds: riparian specialists, forest-interior, and open-edge species, and 6 of 10 species were best explained by specific vegetation features. Differences in vegetation, particularly deciduous tree density and shrub cover, explained part of the variation in abundance of several riparian forest-dwelling species and may be useful in evaluating specific forest management practices. Because deciduous tree density is also positively correlated with buffer width, wide buffers (>100 m) may benefit not only those species associated with coniferous upland forests and forest generalists sensitive to buffer width, but also those species whose abundance is associated with deciduous trees.