Effects of fire severity and fire frequency on the abundance of hollows and hollow-bearing trees

Tree hollows are an essential nesting and denning resource for a diverse range of vertebrate fauna and declines in tree-hollows can lead to declines in hollow-using vertebrates. The forests of south-eastern Australia are experiencing more frequent fires and it has been predicted that a greater area of forest will experience high severity effects from fire under climate change. However, the consequences of changing fire regimes for tree hollows is unclear. We identified the relative effects of the severity of a recent wildfire (the Black Summer fires of 2020) and the frequency of historical fires over 100 years on the number of hollows and hollow-bearing trees in a montane forest ecosystem. We found that the mean number of hollow-bearing trees and total hollows was not significantly different across plots unburnt and burnt in the 2020 fire. Plots that experienced high fire severity had fewer hollow-bearing trees than unburnt plots, but plots that experienced low fire severity had slightly more hollow-bearing trees than unburnt plots. The number of hollows declined with the number of fires that had occurred over the past 100 years. Our results suggest that fire is both an agent of hollow destruction and creation and thus one or more fires may not result in a net loss of hollow-bearing trees at the landscape scale. However, our results imply that a shift towards more high severity burning may result in fewer hollows and hollow-bearing trees across the landscape.