Invertebrate communities in boreal forest canopies as influenced by forestry and lichens with implications for passerine birds

To investigate the effects of commercial forestry on canopy-living invertebrates in the boreal forest, we sampled branches in northern Sweden for invertebrates and lichens from paired natural spruce Picea abies forests and adjacent managed forests that were selectively logged. The study was conducted during late winter, when invertebrate abundance is lowest, and when small differences may be critical to foraging birds. Natural forests had significantly greater invertebrate diversity than managed forests and nearly five times as many invertebrates per branch. The number of large invertebrates (> 2·5 mm, the minimum prey size for foraging passerine birds) was consistently higher in natural forests, with spiders (Araneae), Lepidoptera and Diptera larvae dominating. The number and biomass of invertebrates were related to the abundance of lichens even after controlling for sampling location and branch size. Other studies have implicated forestry in the decline of non-migratory passerine birds in northern Europe through the destruction and fragmentation of forests, but our study indicates that it may also reduce foraging habitat quality through a reduction in lichen abundance.