Modelling habitat and spatial distribution of an endangered longhorn beetle – A case study for saproxylic insect conservation

Saproxylic insects are characterised by their exceptional diversity and high proportion of threatened species. No recent studies have demonstrated the validity of habitat suitability analysis for scientifically based habitat management for these species. We studied the habitat requirements of the endangered longhorn beetle Cerambyx cerdo, a species with a supposed keystone function for the saproxylic insect community living on oaks. We used species distribution modelling based on datasets from Central Europe to understand the species–habitat relationships and to find the environmental variables responsible for habitat selection of C. cerdo. Our results show that the most important parameters, insolation, presence of oak sap, bark depth and the distance from the next colonised tree, are able to predict the presence of C. cerdo very well. A spatial validation procedure revealed very similar predictive power, indicating the general validity of our model. Tree-level parameters were shown to have a stronger effect on the occurrence probability than landscape-level predictors. To improve the tree-level conditions (e.g. insolation on the trunk) habitat management in the form of semi-open pasture landscapes is recommended from which many other taxa will also draw considerable benefit. The provision of such conditions over decades is the essential key in the conservation of this longhorn beetle species. The success of the European network of conservation areas ‘‘Natura 2000’’ heavily depends on broad biological knowledge of the designated protected species. The present paper shows that species distribution models can give valuable contributions for conservation in saproxylic