The effects of fire history on hollow-bearing tree abundance in montane and subalpine eucalypt forests in southeastern Australia

Hollow-bearing trees provide critical habitat resources for forest fauna, yet there is evidence of a ubiquitous decline in the large, old trees most likely to provide this resource. Fire can influence the formation and persistence of tree hollows. In this study, we investigated the effects of stand-level fire history and individual tree attributes on tree hollow abundance in two forest types in Namadgi National Park in the Australian Capital Territory: subalpine woodlands dominated by Eucalyptus pauciflora Sieber ex Spreng (snow gum); and tall-open E. delegatensis R.T.Baker (alpine ash) montane forest. These forests can be differentiated by their distinct response to fire; E. pauciflora resprouts following fire and E. delegatensis reproduces exclusively via seed. We employed a ground-based approach to measure 1044 trees across 36 sites selected by forest type and fire history as recorded since 1920. For both species, hollow abundance decreased with total fire count at stand level and increased for E. delegatensis in response to an extensive wildfire that occurred in the study area in 2003. The probability of a tree containing a hollow increased with tree diameter and if the tree was dead. Our results show that fire frequency and severity have strong implications for tree hollow abundance in montane and subalpine eucalypt forests.