Figure 1. Stages of hollow formation, death and decay of mountain ash trees (Eucalyptus regnans).

The trees surveyed in this study were characterised according to five tree form (TF) categories pictured from left to right: TF1: live trees with no visible hollows (typically young trees); TF2: live trees with visible hollows (typically older, senescing trees); TF3: dead trees in the early stages of decay; TF4; dead trees in the mid-stages of decay; and TF5: highly decayed dead trees. Live trees do not begin to form hollows suitable for arboreal marsupials until they reach an age of at least 120 years.