Severe disturbance sets a lowland mixed-eucalypt forest in south-eastern Australia on a new developmental trajectory

The Black Summer fires of southeastern Australia in 2019–20 were extensive and severe and they may have fundamentally altered the nature of the lowland mixed-eucalypt forests in many places. One hypothesised consequence of such high severity fires is that Eucalyptus sieberi (silvertop ash), a fast-growing, shade-intolerant species that regenerates vigorously from seed, will increase in dominance over large areas. We sampled 64 plots in forests in eastern Victoria that burnt during the 2019–20 bushfires to determine the effect of fire intensity and logging history on the regeneration of canopy species. Seedlings of canopy species regenerated in high abundance and increased in response to increasing seed supply, fire intensity, and prior logging activity. Eucalyptus sieberi was disproportionately successful in recruitment, vigour and competitive position. The increase in openness of the canopy after moderate to high intensity fire or logging may result in parts of the forest becoming dominated by even-aged E. sieberi regeneration. These results suggest that the scale and severity of the Black Summer fires may have set the landscapes of southeastern Australia on a new developmental trajectory in which low diversity E. sieberi stands dominate large areas of forest. • Fire severity varied across the 2019–20 Black Summer bushfires of SE Australia. • Two distinct pathways of post-fire stand development in mixed eucalypt forest. • Low-intensity fire stimulated epicormic sprouting and minimal new cohort. • Moderate-and high-intensity fire made stands more open and new regeneration cohort. • Eucalyptus sieberi had greater representation in the regeneration than in the canopy.