Effects of linear openings in forest canopy on temperate bird communities

Narrow, unpaved roads and paths are a ubiquitous feature of managed forest landscapes worldwide, with the potential to influence bird communities. However, compared to large roads with confirmed negative impacts like fragmentation and noise on birds, the effects of linear canopy openings and other structural changes caused by unpaved small forest roads and paths are less understood. In this study, we investigate the influence of narrow linear openings in the forest canopy caused by forest roads and paths on bird communities in the southern Black Forest, Germany. We aim to understand how these linear canopy openings affect species richness, community composition, and functional traits in forest birds. We surveyed bird communities in four distinct plot types, representing a gradient of ‘canopy openness’: forest interior, forest paths, forest roads, and forest edges. Forest roads and paths represent intermediate conditions between undisturbed interior forests (closed canopy) and a forest edge (open canopy). Our results show that while bird species richness remains relatively similar among those four plot types, the community composition at forest edges differs from the other plot types. In addition, functional traits like body mass and wing shape showed a weak response to the linear canopy openings. These results suggest that although unpaved forest roads and paths potentially introduce resources and structural modifications in the canopy, the effect on the birds seems limited compared to more pronounced habitat transitions, like those on forest edges. Our findings contribute to a better understanding of birds’ responses to linear and small-scale fragmentation introduced by unpaved forest roads and paths. However, there is a need for more research to distinguish the ecological impact on bird communities in temperate managed forests along a gradient of canopy openness.