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UBC Theses and Dissertations

Effects of riparian buffer width on songbirds and forest structure in the southern interior of British Columbia Haag, Devon Adaire


In harvested landscapes, the retention of riparian buffers along streams may mitigate the effects of habitat loss and fragmentation by providing usable habitat for songbirds. To explore this hypothesis, I studied the influence of riparian buffer width on breeding songbirds and forest structure in a high elevation forest of south-central British Columbia. I studied four different buffer widths, consisting of very narrow (2-3 m), narrow (11-15 m), medium (30-34 m) and wide buffers (57-69 m). Buffer and control (unharvested forest) sites were each replicated twice for a total of ten study sites. I conducted spot map surveys and habitat sampling to measure width effects on songbird density and vegetation, and to assess the influence of forest structure on songbird density. To examine habitat use by forest birds, I observed the foraging behaviours and movements of four songbird species: winter wren, yellow-rumped warbler, golden-crowned kinglet and Townsend's warbler. Riparian buffer width had several effects on the songbirds breeding within the study area. First, buffer width influenced songbird community structure and composition. The juxtaposition of clearcut and forest in the study grids containing medium and wide buffers maximized species richness and diversity. As buffer width decreased, generalist and open-habitat species replaced forest species within the study grids; very narrow and narrow buffers provided little habitat for forest songbirds. Second, although changes in forest structure occurred across buffers, width was the most important factor determining the richness and density of forest songbird species. Third, buffer width influenced the movement patterns of foraging songbirds. Individuals in buffers moved greater distances upstream and downstream than they did towards and away from the stream; individuals in unharvested stands moved almost equally in all directions. Overall, there did not appear to be a threshold buffer width beyond which there was a disproportionate loss of species and individuals. Although several common forest species were present to a certain extent in all riparian buffers, forest songbirds would benefit most from buffers ≥ 30 m in width.

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