Longevity and tree ringsLongevity and tree rings

Longevity and tree rings

The wood of the Wollemi Pine produces distinct and annual growth rings (Banks 2002) and, like other members of Araucariaceae, has alternate bordered pits in the walls of tracheids (Heady 2002). The annual growth rings visible in Wollemi Pine wood make it a candidate for dendrochronological study. However, the Wollemi Pine also exhibits strongly asymmetric radial growth, which means that rings may not be visible on all axes every year (Baker & Simkin 2010), leading to a ‘wedged’ appearance of rings when the trunk is viewed as a cross section. This means that the best samples for dendrochronological analysis are complete discs taken from fallen Wollemi Pine trunks, rather than less invasive core samples, to ensure a complete tree ring record. The longest chronologies recorded are in the order of 500 years (from an 18m trunk killed in the 2019-20 fires; Mackenzie et al. unpubl. data) and 400-450 years (from the widest known fallen trunk in the wild with a DBH of c. 90 cm; Banks 2002; Backer & Simkin 2010). A second challenge is using tree rings to estimate tree age as it is likely that stems or trunks originating from seed would have grown for many years before reaching the height at which the sample was taken (often at breast height, 1.35 m for example) although coppice stems on established plants can reach this height within a shorter time (Mackenzie et al. unpubl. data); hence, age estimates of trunks should be considered as minimum estimates only (Baker & Simkin 2010). In the case of coppice trunks on larger individuals, there is no way of knowing how old the individual tree (the genet or subtending rootstock) was before it produced a particular trunk (ramet) and therefore it is impossible to age an individual tree (this is not the case for smaller saplings originating from seed). Nevertheless, the abovementioned chronologies indicate that individual trunks can reach over 500 years old (Banks 2002; Baker & Simkin 2010; Mackenzie et al. unpubl. data).