Green tree retention as a conservation tool for the black woodpecker in managed forests

The black woodpecker, Dryocopus martius, a creator of tree cavities, is considered a keystone species and a priority in terms of forest biodiversity conservation. The aim of this paper was to understand how the structure of managed forests impacts the choice of tree for excavating cavities of the black woodpecker. The study was conducted in an extensive forest complex in northeastern Poland dominated by the pine Pinus sylvestris. The parameters of the cavity trees and surrounding forest were analyzed on different levels to determine what trees and stand types were selected by the black woodpecker. In the period from 2018 to 2021, analyses were carried out for 367 cavities excavated in trees growing in forest areas from 0 to 225 years old. The most numerous cavity trees were between 121 and 160 years old. Cavity trees were found in the stands (62%), in the residual forest patches (19%) and in the single trees remaining after logging (19%). Forty-four percent of all cavities were excavated in dead trees. Black woodpecker nesting stands were characterized by lower canopy closures and low understory and shrub layer cover. We did not find a difference between the diameters or the heights of cavity entrances among the black woodpecker nesting trees growing in different habitat types. The black woodpecker is capable of nesting in small fragments of an old stand and even in single old trees growing in clearcut areas. This is due to the high proportion of dead trees in these habitats, which are preferred by woodpeckers for excavating cavities. Leaving patches of old-growth stands in commercial forests positively affects the habitat formation of the black woodpecker and perhaps, as a consequence, that of other animal species that depend on it.