How long can macadamias live?

A Macadamia Conservation Trust (MCT) project to answer the question of how long macadamias can live will use carbon-dating technology provided by the Australian Nuclear Science and Technology Organisation (ANSTO) to see if counting growth rings is a reliable way of estimating a tree’s age.

Trees grown in temperate climates have clear seasonal growth patterns, making it possible to count a year’s growth for each ring visible on a cross-section of the trunk. This is less likely to be the case for tropical and subtropical rainforest trees, which might spend years waiting under the canopy for their chance to reach for the sun. Once they do start growing, they are likely to have more uniform growth throughout the year and thus have less identifiable annual growth rings.

This means it is possible that growth rates might vary so much for wild macadamias (depending on canopy cover or climatic conditions) that counting growth rings is an unreliable method for determining their age.

The project will test this by comparing the pattern of growth rings with carbon dating of five samples from core to trunk taken from two trees. The trees need to be at least 67 years old (planted in 1955 or earlier), because the nuclear tests at Maralinga (run by the British from 1955 to 1963) caused a spike in the amount of radio-active carbon isotope C14 in most living tissue across Australia at the time. This C14 spike can be used to calibrate carbon dating in samples that were alive over this period.

The photo shows a cross-section of the trunk of the Jordan Tree, a heritage listed tree that was the victim of wildfire around 2020. With permission from the owner and the assistance of the Forest Products Innovation team at Agri-Science Queensland (DAF), a disc has been extracted from the fallen log and sent to dendrologist Dr Kathryn Allen at the University of Tasmania to investigate the growth rings and prepare samples for carbon dating by ANSTO.  The second tree will be a living tree of known age from which small cores will be extracted with no long-term damage to the tree.

MCT hopes to have preliminary results to report by the end of 2022.

Photo Credit: Ian McConachie

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