
FungusPolyporaceae
Fomes fomentarius

Primary white-rot parasite of living Beech; causes extensive heartwood decay that creates the cavities essential for hole-nesting birds.

Major parasite of Silver Birch in northern European forests; often co-occurs with Birch Polypore on the same host.

Saprotrophic and weakly parasitic on Aspen in boreal and montane woodland.

Preferentially nests in Beech trunks infected with Tinder Fungus. The fungus softens heartwood while the bird's cavity promotes further fungal colonisation (Zahner et al. 2012).

Excavates nests in birch and aspen heartwood softened by Tinder Fungus; fungal decay is near-prerequisite for cavity creation.