Retention forestry is a method that can help reconcile timber production and forest biodiversity conservation. The efficacy of retention forestry depends on retained tree characteristics, such as tree species and size, which potentially affect use by wildlife. However, the effects of the characteristics on efficacy of retention forestry are less studied than other factors, such as quantity or spatial patterns of retained trees. We studied 6 saproxylic beetle groups living on 7 types of retained trees (five broad-leaved species, one conifer, and one broad-leaved snag) in harvested conifer plantations 4–8 years after harvesting on central Hokkaido Island, northern Japan. We surveyed beetles on retained trees using trunk window traps to examine (1) which characteristics (tree type, size, and canopy cover) affected abundance at the species and community levels and (2) which combinations of tree types had the greatest effect on beetle species richness. Beetle responses to tree types differed among taxonomic groups. The surrounding canopy cover affected the two groups, whereas tree size had little effect on any group. The optimal combination of tree types varied among the taxonomic groups. Cerambycidae and Disteniidae group and Scolytinae group had high species richness for multiple tree combinations (2–5 types); Erotylidae, Ciidae, and Lucanidae groups had high species richness for fewer combinations (snag or oak). Cetoniinae group was least affected by combinations of tree types. Our results suggest that live oaks and birch snags contribute more to beetle species richness than other tree types, although retaining diverse tree types is essential for conservation of all beetle groups. Our results highlight the importance of individual tree types to improve efficacy of retention forestry for conserving saproxylic beetles. Keywords: Retention forestry; Biodiversity conservation; Plantations; Harvesting; Tree-related microhabitats; Variable retention; Green tree retention
