Habitat requirements of the violet click beetle (Limoniscus violaceus), an endangered umbrella species of basal hollow trees

1. Organisms associated with dead wood (i.e. saproxylic species) are threatened by intensified forest and agricultural management. For a majority of saproxylic beetles the detailed information on their habitat requirements is still lacking, thus hindering efficient conservation information. This also applies to the violet click beetle (Limoniscus violaceus), one of the umbrella species of European saproxylic beetle fauna. This specie needs basal tree hollows for its larval development. 2. We studied habitat preferences of L. violaceus in basal tree hollows using emergence traps installed on 208 trees located in five sites in France. We used logistic regressions and recursive partitioning methods to understand the species-habitat relationships and to identify key environmental variables to predict the occurrence of L. violaceus. 3. The probability of occurrence of L. violaceus in basal hollows increases with increased tree circumference at 30 cm above ground and with increased hollow decay stage. The analysis of threshold values shows that the occurrence of the beetle is relatively high in trees that have a circumference greater than 360 cm, uncertain for those between 235 and 360 cm, and improbable for circumferences lower than 235 cm. Similarly, the occurrence of L. violaceus was probable in advanced stages of hollow decomposition and improbable in early stages. 4. Our results provide non-specialists with helpful habitat features of an umbrella species which is hard to detect. This will increase the ability of conservation managers to identify sites that deserve protection and better monitor the habitat of many saproxylic species associated with basal hollow trees.