Over the hills and far away: linking landscape factors with cavity excavation on living forest trees by the Black woodpecker (Dryocopus martius, L. 1758)

The Black Woodpecker (Dryocopus martius, L. 1758) is the largest primary cavity excavator in Europe. Its cavities represent an essential microhabitat for many other forest species and the knowledge on landscape factors linked with cavity excavation by the Black Woodpecker is needed to support the conservation of this species and associated species. Such relationships should thus be quantified at different scales ranging from the stand to the extended home range. We used cavity maps established by foresters and naturalists to build a large (2689 cavity bearing trees) database distributed over several sites in France. Based on this and on a set of background points, i.e. randomly selected points devoid of cavity in the vicinity, we analysed the effects of stand composition and landscape features (forest cover, forest connectivity and fragmentation) at three different scales around each cavity and background point corresponding to a forest management unit (10ha), the core (100ha) and extended (250ha) home range scales. We showed that indices describing forest continuity (cohesion, landscape shape index) and forest tree species composition (especially the presence of mixed forests) had significant positive effects but that the magnitude varied across the three scales. We notably observed the strongest effects at the core home range scale (100ha), indicating that Black Woodpecker requirements for cavity excavation are more pronounced at this scale. The Black Woodpecker tends to avoid pure conifer-dominated stands to excavate cavities, but benefits from mixed forests, that couple favourable foraging and cavity excavation sites. The bird also prefers continuous forest landscapes with high cohesion and low edge densities. We also showed that the positive effects of forest landscape were generally at higher elevation, indicating context-dependence. Forest planning rarely integrates the landscape patterns. A better understanding of the features linked with cavity excavation by the Black Woodpecker may hence help to better integrate their conservation in forest management planning. Our results also show the importance to maintain mixed broadleaf-conifer forests as well as continuous and well-connected forest landscapes to favour features that benefit primary and secondary cavity nesters.