This assemblage comprises those invertebrates which are most strongly associated with bark and cambium.
This is generally a distinct assemblage of species although there are close links with sap runs and freshly dead trunks and branches which remain sappy. The cambial layer is the richest part of dead and dying wood in terms of availability of nutrients and this is reflected in the range of specialist invertebrates exploiting the situation.
The main distinctions here are in relation to the successional decay of the cambial layer, as it dries out and the overlying bark loosens. Many species are active in the earlier succession, where the bark remains tightly attached and where the cambial layer remains moist, albeit fermentation is proceeding. At the other extreme are species which exploit the under-bark cavities once the bark has been loosened by earlier activity. Many species are described as occurring ‘under bark’ without any record of the degree of tightness of that bark or of the moisture levels beneath.
Many invertebrates are associated with the burrows of early successional beetles such as bark beetles (Scolytinae) and longhorns (Cerambycidae), either a predators, omnivores or commensals. They are only found after the bark has been colonised by those beetle species. Others are associated with fungi, fungal mycelium, and/or moulds that develop in the cambial layer.
Some of the early successional decay species specifically target the cambial layer, burrowing slightly into both the under bark and the outer sapwood. Where this is known the species concerned have been categorised as occurring in the cambial layer. This may also be true of some of the tight bark species. Other species burrow specifically into the bark itself.