Human-induced fragmentation of forests is increasing, yet the consequences of these landscape changes to vertebrate communities are poorly understood. Despite progress in our understanding of how bird communities
respond to forest fragmentation caused by agricultural or urban development, we have little understanding of these dynamics in landscapes undergoing intensive forest management, where mature forest islands are separated by younger forest stands of varying ages. I developed a conceptual framework on vertebrate-habitat relationships in spatially complex landscapes and applied this landscape ecological perspective in the design and implementation of a field study on the relationship between landscape structure and breeding bird abundance patterns in the central Oregon Coast Range. I sampled 10
subbasins (250-300 ha) in each of 3 basins based on the proportion of subbasin in a large sawtimber condition and the spatial distribution pattern of that sawtimber within the subbasin. I systematically sampled each subbasin for birds during the breeding season and developed digital vegetation cover maps for each subbasin. I developed a spatial analysis program for quantifying landscape structure using the Arc/Info Geographic Information System. Using analysis of variance and regression procedures, I quantified the independent effects of habitat area and habitat pattern on several bird species, focussing on species
associated with large sawtimber. Species varied dramatically in the strength and
nature of the relationship between abundance and several gradients in habitat area and pattern at the subbasin scale. Relationships between bird abundance and landscape structure were generally weak; landscape structure typically explained less than one-third to one-half of the variation in each species' abundance among the 30 subbasins. Most species were positively associated with gradients in increasing landscape heterogeneity or fragmentation of their habitats; that is, they were associated with the more fragmented habitats. Only winter wrens showed consistent evidence of association with the least fragmented landscapes. The results are interpreted within the context of the
conceptual framework outlined in the second chapter and within the scope and limitations of the study
