Tree hollow incidence in Victorian state forests

Abstract

Summary The availability of tree hollows in timber production forests is a contentious issue facing forest and wildlife managers in Australia. To integrate conservation priorities for hollow-dependent fauna in forest stewardship, public land managers need information on the quantity and spatial distribution of hollow-bearing trees. This information has previously been lacking, but an extensive hollows database exists in the Victorian Statewide Forest Resource Inventory (SFRI). We use the SFRI to estimate simple stand-level models for the density of hollow-bearing trees, and the density of hollow size classes. Models were of borderline predictive ability but were statistically significant. This is consistent with previous models of hollow incidence that have found hollow formation to be intrinsically stochastic. We then applied these models in a geographic information system (GIS) to generate spatial predictions of hollow availability in Victorian state forests. The resulting GIS layers are available from the Department of Sustainability and Environment (DSE) and are a valuable resource for forest and wildlife managers, researchers and the interested public. We also created tables describing hollow abundance for different forest types, and important stand-level trends in hollow availability emerged. We found that hollow density in ash forests (Eucalyptus regnans, Eucalyptus delegatensis) was consistently low and strongly influenced by the presence of non-ash species that are more susceptible to hollow formation. Hollows occurred in E. regnans forest at particularly low density, with less than 37% of trees having hollows until diameter exceeded 125 cm. The density of hollows in non-ash forests was comparatively greater, with more than 49% of trees containing hollows when their diameter exceeded 75 cm.