The abundance and development of cavities in Eucalyptus trees: a case study in the montane forests of Victoria, southeastern Australia

A study of the abundance of cavities in Eucalyptus regnans, Eucalyptus delegatensis, Eucalyptus nitens, Eucalyptus obliqua and Eucalyptus cypellocarpa is described. The investigation used a database of 2315 living and dead trees with cavities, measured on 523 sites each of 3 ha throughout the montane ash forests of the Central Highlands of Victoria, southeastern Australia. Poisson regression analysis was used to examine the relationships between the number and type of cavities and a range of attributes of trees. These analyses demonstrated that, for all species of trees, the abundance of holes, fissures and hollow branches increased with tree diameter. Log-linear analysis of contingency tables demonstrated that various combinations of cavity types typically occur. Patterns of co-occurrence of cavities changed significantly according to the diameter, height and form of trees. The application of restricted maximum likelihood estimation (REML) for examining multi-level data, enabled the relatioships between the number of cavities, tree characteristics and site parameters to be analysed The characteristics of trees that were important were height, diameter and form. Site parameter that had a significant influence on the total number of cavities in trees included slope, latitude and stand age. This highlights the range of factors, at several measured spatial scales, that may influence the development of cavities in Eucalyptus trees. Although the various relationships derived in this study were highly significant, the statistical models had limited predictive ability. Thus for any given tree the development of cavities will be influenced by site and tree attributes as well as highly stochastic episodic events that may occur during its lifetime. The key findings from the study are discussed in terms of their relevance to forest wildlife management.