Facilitation by wood-boring beetles: Ecosystem engineering effects on soil macrofauna

Deadwood is a critical component of ecosystems, contributing to long-term carbon sequestration, nutrient cycling, and biodiversity maintenance. As a spatially constrained and resource-rich habitat, its invertebrate communities are shaped by fine-scale environmental filtering and species interactions, with fauna-based facilitation playing a key role. Although wood-boring insects are widely recognized as key ecosystem engineers that modify deadwood structure and habitat provisioning, the ecological consequences of their physical tunneling activity are often confounded with concurrent biological processes. As a result, the independent role of structural modification in shaping deadwood macrofauna communities remains poorly understood. This study examined whether simulated longhorn beetle (Cerambycidae) boring, as the physical aspect of ecosystem engineering, influences the diversity and composition of soil macrofauna in deadwood. Using logs from two conifer species, i.e., Picea abies and Abies grandis, we created standardized mechanical drill holes to mimic beetle tunnels and incubated them in a common garden decomposition experiment, for two to three years under similar environmental conditions. Soil macrofauna composition in drilled and undrilled logs was compared to isolate the abiotic effects of cavity formation. Results showed that simulated tunnels altered species composition in some contexts, with taxa such as Isopoda and Diplopoda consistently responding positively to the presence of tunnels. Of particular interest was the positive effect of tunnel boring on the abundance and diversity of soil macrofauna in P. abies after 35 months, which seemed consistent with the positive effect on wood decomposition rate and water holding capacity. These findings provide experimental evidence that small-scale structural heterogeneity made by ecosystem engineers can benefit low-mobility and environmentally sensitive soil macrofauna species by offering microhabitat refuges, while the broader consequences for decomposition are context-dependent and likely shaped by the interaction between physical modification and the biological processes linked to beetle activity.