Alpine ash (Eucalyptus delegatensis) and the related mountain ash (E. regnans) are tall forest trees endemic to the mountains of southeastern Australia. Unlike most eucalypts, they do not readily resprout following fire. They regenerate from seed (i.e. obligate seeders), typically after high-severity fires, but have no long-term soil seed bank. They require around 20 years to reach reproductive maturity, and are vulnerable to local extinction if another fire occurs before the young trees set seed.
A series of wildfires throughout the Australian Alps in 2003, 2006 and 2009 burnt over 87% of the Victorian distribution of alpine ash. These fires, ignited by lightning, initiated regeneration, but some regenerating stands were reburnt by the later fires, causing population declines or local extinction. In some areas where regenerating alpine ash was killed, the species has been re-established by aerial sowing of seed. However, this intervention is impractical over large areas of forest because of costs of aerial sowing and limited availability of seed. Most alpine ash populations are currently in an immature state after these fires, rendering them vulnerable to local extinction if reburnt. Regenerating stands of alpine ash could also be more fire-prone than mature stands, but the effect of stand age is small relative to that of climate on the frequency of high-severity fires.
A projected warming and drying climate, possibly with more lightning, is likely to lead to increasingly frequent, severe fires. The hotter, drier conditions will also constrain the capacity of both alpine ash and mountain ash to recover from disturbance, by reducing tree growth, seed production and seedling establishment. Reduced growth, combined with shorter intervals between high-severity fires, will result in ‘interval squeeze’, which can threaten these species’ persistence as the climate changes.