Effects of landscape heterogeneity on bird communities in temperate, boreal, and montane forests – a review

Bird populations in Europe and North America have been strongly declining for the last 40 years. As mobile organisms, bird species are sensitive to landscape patterns; therefore, landscape effects on bird communities need to be understood to set relevant conservation measures. However, forest bird communities have received much less attention than their counterparts in agricultural landscapes in this respect. In this systematic review, we investigated the effects of landscape heterogeneity on bird communities in forest contexts by searching for empirical studies conducted in the boreal, montane, and temperate biomes. We found 45 articles from which we extracted 1272 single results (i.e. tested relationships between landscape and biodiversity metrics). We found that most of the articles studied local alpha-diversity (78%; 22% for landscape gamma-diversity) during the breeding season (87%). In contrast, most of the significant results were related to bird gamma-diversity, indicating a positive effect of landscape heterogeneity. Most of the tested landscape metrics were related to compositional heterogeneity (74%). Overall, habitat amounts had a large positive effect on their related communities (i.e. forest amount on forest bird species). However, forest composition variables (e.g. broadleaf forest proportion) mostly led to non-significant effects. While we found antagonistic results depending on bird habitat preference, groups based on migration strategy were largely unresponsive to landscape variables. However, we failed to find a consistent scale of effect across studies. We discuss the potential landscape mechanisms at play, such as niche partitioning, edge effects, and habitat complementation. We recommend better acknowledging forest ecosystem complexity and variability in future forest landscape studies and better recognition of bird habitat requirements beyond the breeding season (including overwintering sites and migration stopovers).