Forests ecosystems sustaining most of the terrestrial biodiversity are under increasing anthropogenic pressure. Both the protection of the remaining natural forests and the mitigation of the negative effects of silviculture are of primary conservation concern. Clear-cut areas are the main open habitats in production forests, potentially offering temporary refuge for species from declining semi-natural grasslands. Although several groups of flower-visiting insects, including butterflies, have been reported to thrive in clear-cuts, a taxonomically comprehensive understanding of the insect fauna utilising these habitats is lacking. In this study, we examined the assemblages of nocturnal macromoths (Lepidoptera: Marcoheterocera) in forest clear-cuts of varying age (2–6 years) and regeneration regimes (natural vs. artificial) in Northern Europe. Using automatic sugar-bait traps, we sampled 50 clear-cuts and three pairs of forest-grassland reference sites over two summers. Nocturnal moths of the clear-cuts were highly diverse, harbouring 50% of the regional species pool of noctuids. However, several common grassland-associated species, as well as a few forest species, were nearly absent. Although the similarity between clear-cut and forest assemblages increased with clear-cut age, the recorded characteristics of the clear-cuts had little overall influence on moth assemblages. Artificially regenerated clear-cuts, characterised by a more open vegetation structure, supported slightly higher moth species richness and diversity compared to naturally regenerating sites.

Policy implications: Our results highlight the role of forest clear-cuts in supporting insect biodiversity. As such, clear-cuts warrant special consideration as a distinct habitat type. However, the effects of clear-cut regeneration and maintenance methods on assemblages of moths appear weaker than in various other insect groups. More importantly, the absence of several common grassland species highlights that clear-cuts cannot fully replace traditional open habitats. This underscores the importance of conserving semi-natural grasslands.