Wild population structureWild population structure

Wild population structure

The prolific coppicing habit of wild Wollemi Pine makes it difficult to delineate genetically distinct individuals in the field. In lieu of completed population genomic analyses, putative individuals have been defined as discrete clumps of stems or trunks inferred to share a common base. The wild population is composed of adult, juvenile and functionally juvenile individuals. Male pollen cones develop on juvenile trees several years before the first female seed cones, and individuals are regarded as adults once they produce female seed cones. Adult trees that suffer complete loss of their mature trunks after fire, windthrow or impacts from falling rocks and trees, may enter a secondary juvenile phase while replacement stems resprout and mature (Mackenzie & Auld, in press). Such functionally juvenile individuals are expected to have higher survival and faster growth and maturation than true juveniles (those yet to produce a mature trunk since establishing from seed) due to well-developed adult root systems in the former (Mackenzie & Auld, in press).

A comprehensive demographic inventory of the wild population was undertaken in 2020 and 2021 (after the 2019–20 bushfire season). This entailed updated assessments of the boundaries between putative individuals and their reproductive status (adult, juvenile or functionally juvenile) (Mackenzie & Auld, in press). In addition, a number of previously undetected juvenile and adult trees were identified on high cliffs adjacent to known stands(Mackenzie et al. unpubl. data).

As of June 2024, 45 adult trees remain in the wild with 19 of these in the largest stand (Table 1; Mackenzie & Auld, in press). The population includes a further 34 true juveniles and 12 functional juveniles; however, 47% and 75% of these, respectively, were completely top-killed in the 2019–20 fires and currently persist as vulnerable basal resprouts (Mackenzie, Clarke and Auld, unpubl. data). A further 113–183 immature individuals (seedlings, juveniles and functional juveniles) were killed in the fires including 92–95% of the pre-fire bank of smaller juveniles (those < 2m tall), among which were many individuals over 20 years old, with some up to 60 years old (Mackenzie, Clarke and Auld, unpubl. data). This small juvenile bank is expected to re-establish over the next 20–30 years via ongoing annual seed production in adult trees (Mackenzie et al. 2021); However, the losses of larger juveniles will take many more decades to recover. The first systematic post-fire seedling surveys are scheduled for summer 2024-25 (B. Mackenzie, pers. comm.).

Table 1 Wollemia nobilis post-fire population structure