Impacts of changing fire regimes on hollow-bearing trees in south-eastern Australia

Tree hollows are important structural habitat features for secondary cavity‐nesting birds, however, there has been limited research on how fire severity and frequency affect hollow abundance. Following a mega‐fire on Kangaroo Island during the 2019–2020 Australian bushfire season, we conducted an opportunistic post‐fire assessment of the fate of 144 monitored hollows in Eucalyptus cladocalyx and Eucalyptus leucoxylon trees used by endangered glossy black‐cockatoos (Calyptorhynchus lathami halmaturinus) and yellow‐tailed black‐cockatoos (Zanda funerea). We investigated the relationship between burn severity, inter‐fire interval, tree species and landscape position on the likelihood of tree hollow loss. We also compared the occupancy of nest boxes by both cockatoo species in fire‐affected catchments pre‐fire (2015–2017; 59 nest boxes) and post‐fire (2020–2022; 52 nest boxes). Surveys revealed that 64.4% of monitored tree hollows within the burnt area were destroyed, as were the trees that contained them. Most monitored tree hollows (76.9%) were in areas that had not experienced fire in >50 years prior to the 2019–2020 fires. Tree hollow loss in 2020 was 29 times greater than the mean annual loss of 1.6% recorded in the 22 years prior. Burn severity, inter‐fire interval, landscape matrix and tree species were poor predictors of hollow loss. However, increasing distance from forest edge slightly increased the probability of hollow loss. Post‐fire, the proportion of nest boxes used for nesting by glossy black‐cockatoos per annum increased to 0.70 ± 0.09, compared to 0.50 ± 0.03 pre‐fire. However, the proportion of nest boxes used for nesting by yellow‐tailed black‐cockatoos per annum remained similar (post‐fire 0.32 ± 0.12; pre‐fire 0.28 ± 0.05). The mega‐fires on Kangaroo Island in 2019–2020 resulted in tree hollow loss on a much larger scale than recorded in the 22 years prior, and subsequently, nest boxes have become an important resource for the endangered glossy black‐cockatoo.

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How an unprecedented wildfire shaped tree hollow occurrence and abundance—implications for arboreal fauna

Wagner,

Baker,

Nitschke

2024

fire ecol

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Background Tree hollows are an important habitat resource used by arboreal fauna for nesting and denning. Hollows form when trees mature and are exposed to decay and physical damage. In the absence of excavating fauna, hollow formation can take up to 200 years in Australian temperate Eucalyptus forests, making tree hollows a critical but slow forming habitat feature. The increasing frequency and severity of wildfires due to climate change has led to increased concern about the landscape-scale loss of nesting space for arboreal fauna, including endangered species such as the folivorous southern greater glider (Petauroides volans). To understand patterns of nesting resource availability, we assessed drivers of hollow occurrence in southeastern Australian mixed-species Eucalyptus forests and quantified the effects of an unprecedented large-scale wildfire, the 2019/2020 Black Summer bushfires, on hollow occurrence and abundance. Results Tree size and shape, as well as site productivity and topography, were important predictors for hollow occurrence both before and after the fires. The occurrence of the southern greater glider was strongly dependent on high proportions of hollow-bearing trees. While high fire severities had a negative impact on southern greater glider occurrence, the number of hollow-dependent arboreal species was not affected. While the wildfires significantly reduced hollow abundance, we did not find significant effects on hollow occurrence. Fires altered the relationship between tree size and hollow occurrence expressed as a change in the probability of hollow occurrence, with a higher likelihood at smaller tree sizes after the fires. Conclusions Our findings suggest that post-fire nesting space may be reduced at the tree-scale, while at the stand-scale, hollow-bearing trees persist as biological legacies. These persisting trees can support the recovery of hollow-dependent arboreal fauna, such as the endangered southern greater glider by providing denning and nesting space. Hollow-bearing trees that survived the fires have the potential to form new hollows faster compared to undisturbed mature trees.

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Impacts of changing fire regimes on hollow-bearing trees in south-eastern Australia

Cited by 4 publications

References 63 publications

Mature forest habitat mitigates the decline of an endangered greater glider population through a widespread disturbance event

Mature forest habitat mitigates the decline of an endangered greater glider population through a widespread disturbance event

The impact of a mega‐fire on tree hollow loss and nest box occupancy by secondary cavity‐nesting cockatoos

How an unprecedented wildfire shaped tree hollow occurrence and abundance—implications for arboreal fauna

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