Cavities serve as den sites, shelters, and breeding sites for many animal species. Maintaining cavity resources for cavity-users is crucial, especially in landscapes where the majority of the forest has been modified. Furthermore, information on both the distribution of the cavity tree and the tree selection by the animal is needed to determine suitable management plans. We investigated the distribution of cavity trees at the forest stand and individual tree levels, and the selection by the Siberian flying squirrel (Pteromys volans) in the remnant oak forests and riparian forests in an agricultural landscape. We developed 120 circular survey plots (20m radius) in the study site and recorded the species, diameter at breast height (DBH), and tree status (live/dead) of trees >10cm DBH. We also searched and marked all cavity trees. In winter, all the cavity trees were revisited and occupation by flying squirrels was confirmed by accumulated scats at the base of the trunk. Using a GLM, we compared the cavity occurrence between forest types and for each tree species. The relationship between cavity occurrence and DBH was also investigated. Furthermore, we used a GLMM to determine stand or tree characteristics that determined cavity use by the flying squirrels.

Results/Conclusions

We recorded a total of 440 cavity trees (339 in riparian and 101 in oak forests). Cavity occurrence was higher in riparian forests. Snags were more likely to carry cavities than live trees, but they provided only a limited size (mostly <30cm DBH) and number (23%) of cavity trees compared to live trees. With respect to live trees, the DBH class with the highest probability of cavity occurrence differed from the class with the highest number of cavity trees in the most tree species, indicating that the tree size that contributes potentially and actually to the availability of cavity trees do not coincide. The Siberian flying squirrels had used 23 cavity trees, with the highest probability of selecting trees in riparian forests with a diameter of 56cm. Our results indicate that the distribution of cavity trees differs between forest types, and that riparian forests are a particularly important source of cavity trees and winter den site of the Siberian flying squirrel. Furthermore, since the probability of cavity occurrence is relatively high at DBH of 50-60cm in trees of riparian forests, it is important to maintain abundance of trees at this size to conserve suitable cavity trees for this strictly arboreal rodent.