This category is subdivided into three key components: a general association with dead and decaying trunks, stumps, branches and twigs, partly related to the dead and decaying sapwood; the bark and cambial layer; and subterranean decay provided by roots and trunk bases, and buried wood generally.
These are all features found in young, mature and older trees alike, and so do not have obvious associations with old growth situations, unlike the heartwood decay fauna. There are situations however where an association with old growth is apparent, e.g. where the under-bark assemblage requires the tree trunk to be of sufficiently large girth and age to be providing extensive development of bark cavities occupied by spiders and thereby providing habitat for specialist cobweb beetles (Dermestidae).
It is important to recognise that standing dead and decaying wood can be part of a living tree as well as a dead tree.
There are many cases where a particular species can be categorised to more than one of the four components, e.g. where the larvae develop beneath bark on standing dead trunk wood. In many cases the current level of knowledge restricts the ability to categorise the species, and some species appear to defy such categorisation.