The cavity is substantial: an entrance roughly eight to twelve centimetres across, a chamber that may be 40 centimetres deep, most often in a beech or a large pine with a straight branch-free trunk. Excavation takes weeks, and a pair may work on several before settling.
Because the species usually cuts a fresh hole rather than reoccupying an old one, the forest accumulates a stock of large cavities that nothing else can make. The boreal owl and the common goldeneye are strongly associated with black woodpecker holes, and stone martens, bats and social insects use them too. Forest managers now treat black woodpecker presence as an indicator of structural maturity.
The dependency runs the other way as well: the bird requires large old trees and standing deadwood with carpenter ant colonies. In intensively managed forests both are scarce. How large a stand must be to sustain a pair varies with region and forest type, and published territory sizes differ widely.