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

The Black woodpecker (Dryocopus martius, L. 1758) is the largest primary cavity excavator in western Europe. Its cavities represent an essential microhabitat for many other forest species but the landscape factors linked with cavity excavation by the Black woodpecker are poorly known and rarely been quantified at the scale of the home range. We used cavity maps by foresters and naturalists to build a large (2689 cavity bearing trees) database distributed over 11 sites in France. Based on this and on a set of background points, we analysed the effects of stand composition and landscape features (forest cover, landscape connectivity and fragmentation) at three different scales around each plot corresponding to a forest management unit (10ha), the core (100ha) and extended (250ha) home range scales. We showed that landscape shape index and forest composition (mixed forests) had significant 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 tend to avoid conifer-dominated stands to build cavities, but benefits from mixed forests, that couple favourable foraging and cavity excavation sites. The bird also prefers homogeneous forest landscapes with low edge densities. These results vary with precipitation and slope with stronger effects of landscape in wetter climates and higher slopes. Forest planning rarely integrates the landscape patterns in western temperate Europe, a better understanding of the features that are 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 connected forest landscapes to favour features that benefit forest biodiversity at the large scale.