The influence of fire and termites on tree hollow development in an Australian tropical savanna

Tree hollows are important habitat resources for wildlife globally. In the tropical savannas of northern Australia, the abundance of tree hollows is influenced by both fire and termites. With the regular application of prescribed fire in these ecosystems, it is important to understand the implications of fire management on important habitat resources – especially when applied over the long-term. This study uses a long-term fire experiment (18 years of applied fire treatments) with targeted termite and tree hollow surveys to investigate how the proportion of stem hollowing and abundance of hollow entrances are affected by termites and different long-term fire regimes. We used sonic tomography in a novel application to non-destructively estimate tree stem hollowing. Trunk diameter was identified as the strongest predictor of both stem hollowing and hollow entrance abundance, with larger trees having a greater proportion of the stem hollowing and greater number of hollow entrances. The proportion of stem hollowing tended to be greater closer to the base of the tree, and the number of hollow entrances was greater in Eucalyptus miniata than E. tetrodonta. While the proportion of stem that was hollowed did not influence the number of hollow entrances, the presence of any hollowing at 1.3 m was associated with more hollow entrances. We did not detect an effect of fire activity on stem hollowing or the abundance of hollow entrances at the individual tree level, and it may be that these effects are only detectable at the stand level due to changes in tree demographics with varying fire regimes. As large trees tend to have more hollow entrances, management to promote habitat for wildlife should focus on fire regimes that avoid the loss of large trees in the landscape.