Tree species influence the assemblages of trunk-dwelling arthropods and saproxylic beetles on fire-damaged trunks in a boreo-nemoral forest

Wildfire is the dominant natural disturbance in boreal ecosystems, yet the extent to which recently burned trees of different species filter arthropod assemblages remains unclear. We quantified trunk-ascending arthropods and saproxylic beetles on fire-damaged trunks of four common boreal trees – Betula pubescens, Populus tremula, Pinus sylvestris and Quercus robur – in a 2021 burn in south-eastern Sweden. Twelve collar traps (three per species) operating for 189 days captured 9178 arthropods from 16 higher taxa, including 1427 beetles (96 species, 13 of which are red-listed). The overall arthropod assemblage varied only weakly with host tree and was primarily driven by Collembola, whereas beetle composition differed markedly, with host species identity explaining 52 % of the multivariate variation. B. pubescens supported the highest beetle richness (52 species) and P. tremula the greatest abundance (848 individuals, 60 %). Species turnover among hosts was high (Jaccard similarity = 0.17–0.36). Thirty beetle species, among them the Vulnerable Dircaea australis and Near-Threatened Triplax rufipes, showed significant preferences for a single tree species. Thus, post-fire trunks retain strong host specificity for beetles but not for the broader arthropod fauna; conserving a mosaic of burned stems across multiple tree species will maximise beetle richness and retain threatened taxa.