| Summary: | Fennoscandia is primarily covered in forests, but modern forestry has dramatically altered the landscape. Mixed-species and uneven-aged forests with natural gap rotations of 250 years were replaced by dense, even-aged stands that are clearcut every 80-120 years. Only 1.7% of productive boreal forest has never been clearcut in Norway, creating a patchwork of stands homogenized in structure, age, and composition. This transformation has removed niches and degraded habitats for myriad forest-dependent species. Deadwood- and cavity-dependent birds, insects, lichens, plants, and other taxa have been disproportionately threatened by the removal of standing dead trees (snags) in harvests and thinnings. Many cavity-nesting birds (hereafter cavity-nesters) have been deprived of their primary nesting and foraging cover. I used a quasi-experimental approach to quantify changes in habitat variables and bird activity. Acoustic recorders were placed in 10 locations throughout southeastern Norway from 6 June to 22 July 2023. Each location contained a pair of forest sites – one that had been clearcut 40-80 years ago (CC) and one that had never been clearcut (NN). These sites are part of the EcoForest project (https://ecoforest.no/), a collaborative effort to study long-term changes in forest biodiversity caused by past forest management. Automated analysis of all 3,026 h of audio recordings using BirdNET detected 169 bird species (<165 after validation). Neither total species richness nor Shannon diversity was higher in either SiteType (CC or NN), but diversity was more variable in NN. Far more recordings per day per site of excavators and old-growth icons were recorded in NN, while significant, marginally higher numbers were found for weak excavators and secondary nesters in CC. A declining keystone species, Picoides tridactylus, and an apex predator, Accipiter gentilis, were 7 and 9 times more frequently detected in NN, respectively. NN had 1 more cavity per habitat survey plot (14/ha), habitat trees measuring 8 cm DBH ...
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