Limited short-term benefits of stub retention for open-canopy songbirds in foothills forests

Stubs—wildlife trees topped above 2.5 m in logged stands—provide documented benefits to cavity-nesting birds as they decay into snags, but their effects on open-canopy songbirds colonizing young harvests are poorly understood. We evaluated whether stubs directly increased habitat use through perch provisioning or indirectly through enhanced vegetation in 46 paired stubbed and stubless sites in 1–2 year post-harvested stands in the foothills of Alberta, Canada. Using Autonomous Recording Units and amplitude-based distance truncation, we measured vocal activity rate of breeding songbirds at fine detection radii and used piecewise structural equation models to partition direct and vegetation-mediated effects. Direct effects of stubs were inconsistent; positive for Dark-eyed Junco ( Junco hyemalis ), negative for Alder Flycatcher ( Empidonax alnorum ), and neutral for Lincoln's Sparrow ( Melospiza lincolnii ). Vegetation—decayed coarse woody debris (CWD) for Dark-eyed Junco, shrub cover for Alder Flycatcher—positively predicted vocal activity, but these vegetation pathways did not translate into an overall positive effect. Stubbed sites did not consistently contain more decayed CWD, resulting in no net indirect benefit for Dark-eyed Junco. For Alder Flycatcher, the positive indirect effect through shrub cover was offset by the negative direct effect. No species showed an overall positive response to stub retention. Our findings suggest stubs in their current form provide minimal short-term benefit to open-canopy songbirds; their conservation value likely increases as they decay into snags used by cavity- and bark-foraging species. We recommend stub management prioritize structural characteristics relevant to cavity users and that effectiveness evaluations target later regeneration stages when such species are more likely to be present.