Fig. 1. Locations of study plots (WNP - Wigry National Park, KBNR - Kuriańskie Bagno Nature Reserve).

Fig. 2. Comparison of cavities excavated by (a) Black Woodpecker (a), and (b) Great Spotted Woodpecker (b). A Tengmalm’s Owl uses a cavity excavated by a Black Woodpecker (c), and a Black Woodpecker is photographed in the process of excavating a cavity in a live pine tree (d). (Photography by G. Zawadzki).

Fig. 3. Relative frequency of occurrence of cavity trees of different species, by age intervals (numbers above bars denote absolute numbers of cavity trees of the given species in the given age category).

Fig. 4. Mean density of cavity trees, live and dead, by age intervals (vertical lines denote standard error of mean value; the same letters located by mean values indicate homogeneous groups, Tukey’s HSD test, p < 0.05).

Fig. 5. Total volume of cavity trees, live or dead, by age intervals (vertical lines denote standard error of mean value; the same letters located near the median values indicate homogeneous groups, Tukey-test HSD, p < 0.05).

Fig. 6. Mean density of trees with cavities excavated by the Black Woodpecker or Great Spotted Woodpecker, as well as natural cavities, by age intervals (vertical lines denote standard errors of mean values, while the presence of the same letters by mean values indicates homogeneous groups, Tukey’s HSD test, p < 0.05.