Effects of Linear Openings in Forests on Temperate Bird Communities

Narrow, unpaved forest roads and paths are a ubiquitous feature of managed forest landscapes worldwide, with the potential to influence bird communities. However, compared to large roads, the effects of structural changes to the understory and canopy generated by unpaved forest roads and paths are less understood. In this study, we investigate the influence of narrow linear openings in the forest caused by forest roads and paths on bird communities in the southern Black Forest, Germany. We surveyed bird communities in four distinct plot types, including two "linear openings": forest interior, forest paths, forest roads, and forest edges. Forest roads and paths were expected to represent intermediate conditions in terms of openness between interior forests and a forest edge. We aim to understand how these linear openings affect birds' species richness, community composition, and functional traits. Our results show that while species richness remains similar among plot types, the community composition at forest edges differs. The indicator analysis reveals indicator species for each type of plot. In addition, functional traits like body mass and wing shape showed a weak response to the linear openings. The findings suggest that although unpaved forest roads and paths potentially introduce resources and structural modifications in the forest structure, the effect on the birds seems limited compared to pronounced habitat transitions, such as forest edges. These narrow linear infrastructures are often necessary for forest use by humans and can be unnoticeable for birds when carefully planned on a small scale. Nevertheless, forest managers should not overlook broader-scale effects (e.g., potential habitat loss, predation). Our findings contribute to a better understanding of birds' responses to linear and small-scale fragmentation introduced by unpaved forest roads and paths. However, more research is needed to distinguish the ecological impacts and management implications for bird communities in temperate managed forests along a gradient of linear openness.