Drivers of deadwood colonization by ants in a temperate forest

Deadwood represents a key structural component of forest ecosystems, yet the ecological role of ants within saproxylic communities remains largely overlooked compared to other invertebrate groups. In this study, we investigated ant colonization patterns across 5826 deadwood fragments of Quercus spp. and Castanea sativa in a temperate woodland of Northern Italy. We quantified how wood characteristics (diameter, length, hardness, decay class), tree species, topographic variables, and fissuring influence colonization probability, colony composition, and interactions with other saproxylic taxa. Ants colonized 39.1% of Quercus fragments and 13.4% of C. sativa, with colonized pieces showing significantly larger diameters and lengths. Hardness and decay class exhibited species-specific effects: colonized oak fragments were harder, whereas colonized chestnut fragments were softer and more decomposed. Across 13 ant species, colony composition varied markedly, with incipient and mature colonies occupying distinct microhabitats. Temnothorax alienus and Temnothorax unifasciatus were strongly associated with complete colonies, while Lasius emarginatus and Crematogaster scutellaris were more frequently represented by founding queens or early-stage colonies. Multivariate generalized linear model analyses showed significant effects of tree species, topographic parameters and deadwood characteristics on community composition. Our study demonstrated that artificial fissuring significantly increased colonization by ants and saproxylic beetles. Overall, our findings show that ants act as selective colonizers of deadwood, responding to fine-scale structural and microenvironmental gradients, and contribute to the formation of complex saproxylic assemblages. This study strengthens the ecological basis for forest management strategies that integrate deadwood conservation and recognize ants as relevant ecosystem engineers within decomposing wood.