The potential role of volatile organic compounds on the colonisation of deadwood by saproxylic beetles.

Volatile organic compounds (VOCs) emitted by deadwood are increasingly recognised as key olfactory cues used by saproxylic beetles to locate suitable substrates, yet their role during colonisation remains poorly understood. To address this, we quantified VOC emissions and beetle assemblages while experimentally disentangling the main ecological drivers of the deadwood volatilome (tree species, sun exposure). We exposed 1200 freshly cut branches of oak, beech, spruce, and pine across Central Europe. To mimic natural variation in deadwood and disturbance, bundles were either sterilised (reducing endogenous fungi), inoculated with a brown rot fungus (Fomitopsis pinicola) or a white rot fungus (Fomes fomentarius), or burned. From each bundle, we sampled 448 substances, 89 of which were identified as VOCs, and reared 134 saproxylic beetle species. Broadleaf and conifer species emitted distinct VOC profiles that matched beetle tree-type preferences. In conifers, bark beetles, longhorn beetles, and jewel beetles were associated with different chemical cues, whereas taxonomic separation was not observed in broadleafs. Although treatments altered VOC composition, they did not explain beetle colonisation. Our study shows that VOCs emitted during early decay are associated with distinct beetle assemblages. The VOC composition varied with tree species and treatments, indicating that chemical variation reflects the influence of multiple ecological factors. These findings suggest that tree-species diversity enhances chemical heterogeneity in deadwood, which is linked to broader beetle assemblages. Forest conservation efforts may therefore need to consider the role of chemical variation in deadwood, as it could influence saproxylic colonisation and biodiversity management.