Small population and restricted geographSmall population and restricted geographic distribution

Small population and restricted geographic distribution

The wild Wollemi Pine population consists of just 45 mature individuals and 46 juveniles (Table 1) which occur over an area of only 4 km2. These characteristics increase the species risk of extinction due to a catastrophic event, such as a severe bushfire, drought or disease outbreak.

The bimodal size structure of the wild Wollemi Pine population is indicative of an apparent recruitment bottleneck that remains a serious concern for the population’s long-term viability. Zimmer et al. (2014) suggested that the infrequency of successful transitions between juvenile and adult Wollemi Pine is typical of many rainforest species that maintain banks of seedlings and small juveniles that respond to stochastic increases in resource availability (often via canopy gap formation; Whitmore 1989). However, subsequent research suggests that this recruitment bottleneck is fire-related (Mackenzie et al. unpubl. data). The near-complete loss of the seedling and small juvenile bank in the 2019–20 bushfires is a significant concern. Re-establishment of this juvenile bank from seed will require a fire-free period of at least 20–30 years (Mackenzie et al. 2021), and many more decades without fire for replacement of larger individuals, which may be unlikely without management intervention due to increasing trends in fire risk along the east coast (Dowdy et al. 2015).