Does high fire frequency compromise structural integrity of a large eucalypt?

Globally, fire regimes are changing with more frequent fires, longer fire seasons, and burning in places and times where fire was once rare. To mediate fire risk, prescribed burning is often used to reduce fuel but in some ecosystems increasing fire frequency has been implicated with negative ecological outcomes. Here, we investigate interactions of fire frequency and basal hollow development, a precursor to structural failure, on a giant tree species (red tingle, Eucalyptus jacksonii ) in southwestern Australia. We stratified sampling (n = 622 large trees) by fire history data (1953–2021) to create 1-ha areas of red tingle forest by number of times burnt: long unburnt (LUB; 0); low (1−3), moderate (4−6); high (7 +). For each area we quantified: large tree (>100 cm diameter at breast-height) density, tree diameter, and basal hollows (proportion and extent) across and between stands. Mean large tree density across all stands was 15.7 ha −1 with the lowest density in high fire frequency stands (14.0 ± 0.8). For our smallest size class trees (100 cm DBH), high fire frequency stands were more likely to have basal hollows (31 % of trees) compared to LUB (20 %); low (17 %); and moderate (21 %). Our work shows a positive association between fire frequency and the frequency, size, and initial development of basal hollows. The implication of this research is that increased fire frequency may be resulting in losses of large individuals, potentially leading to a demographic squeeze. Future climate and fire scenarios will require transparently weighing up ecological impacts alongside fire risk to inform best practice land management. • High fire frequency stands had the lowest density of large red tingle trees. • Basal hollows in our smallest diameter size classes were more prevalent in high fire frequency stands. • We developed a new, and easily executable monitoring protocol for assessing tree structural vulnerabilities to disturbances. • Increases in fire frequency may be leading to losses of large individuals and a demographic squeeze in the population.