There is a succession of invertebrates colonising and later dying out as the heartwood is gradually decayed by specialist decay fungi (predominantly the larger bracket fungi), cavities form, and debris accumulates in the base and composts down into wood mould.
Heartrot within large tree trunks provide large scale habitats, but hollowing may also take place in smaller girth trunks. Smaller scale pockets of heartwood decay occur where lateral branches have died and broken off, allowing access to a different range of heartwood decay fungi, notably Polyporus squamosus. Such situations are generally termed rot-holes. They tend to be exposed to the weather and become wetted by rainfall and even flooded to form aerial pools. In a vigorous living tree, these pockets of decay may be actively compartmentalised by the tree. In other cases, the small high pocket of decay may extend deep into the centre of the trunk and develop downwards to hollow the trunk.