Landscape-scale disturbances and changes in bird communities of boreal mixed-wood forests

Bird community response to both landscape-scale and local (forest types) ch anges in forest cover was studied in three boreal mixed-wood forest landsca pes modified by different types of disturbances: (1) a pre-industrial lands cape where human settlement, agriculture, and logging activities date back to the early 1930s, (2) an industrial timber managed forest, and (3) a fore st dominated by natural disturbances. Birds were sampled at 459 sampling st ations distributed among the three landscapes. Local habitat and landscape characteristics of the context surrounding each sampling station (500-m and 1-km radius) were also computed. Bird communities were influenced by lands cape-scale changes in forest cover. The higher proportion of early-successi onal habitats in both human-disturbed landscapes resulted in significantly higher abundance of early-successional bird species and generalists. The me an number of mature forest bird species was significantly lower in the indu strial and pre-industrial landscapes than in the natural landscape. Landsca pe-scale conversion of mature forests from mixed-wood to deciduous cover in human-disturbed landscapes was the main cause of changes in mature forest bird communities. In these landscapes, the abundance of species associated with mixed and coniferous forest cover was lower, whereas species that pref erred a deciduous cover were more abundant. Variation in bird community com position determined by the landscape context was as important as local habi tat conditions, suggesting that predictions on the regional impact of fores t management on songbirds with models solely based on local scale factors c ould be misleading. Patterns of bird species composition were related to se veral landscape composition variables (proportions of forest types), but no t to configuration variables (e.g., interior habitat, amount of edge). Over all, our results indicated that the large-scale conversion of the southern portion of the boreal forest from a mined to a deciduous cover may be one o f the most important threats to the integrity of bird communities in these forest mosaics. Negative effects of changes in bird communities could be at tenuated if current forestry practices are modified toward maintaining fore st types (deciduous, mixed-wood, and coniferous) at levels similar to those observed under natural disturbances.