Traditional Fire Practices Key to Tree's Survival

Key Points

• Some culturally significant trees on Minjerribah (North Stradbroke Island) have persisted for up to more than 500 years.
• The presence of large old Bugari (Cypress pine) trees suggested a long history of cultural burning by the Aboriginal people using mild fires and the importance of continuing these practices in protecting these trees
• Radiocarbon dating at ANSTO supported the investigation

Radiocarbon dating at ANSTO's Centre for Accelerator Science provided strong evidence that some culturally significant trees on Minjerribah (North Stradbroke Island) have persisted for up to more than 500 years.

The study trees varied in age from 63 to 531 years.

A research team led by the Department of Environment, Tourism, Science and Innovation, Queensland Herbarium and Biodiversity & Science, undertaken in partnership with the Quandamooka Yoolooburrabee Aboriginal Corporation (QYAC), have published the findings in Ecological Management and Restoration.

Lead author Dr Michael R Ngugi is a Principal Conservation Officer with the Queensland Department of Environment, Tourism, Science and Innovation.

"The presence of large old Bugari (Cypress pine) trees suggested a long history of cultural burning by the Aboriginal people using mild fires and the importance of continuing these practices in protecting these trees", said Dr Ngugi.

"Bugari are killed by canopy-scorching bush fires but survive low-intensity ground-layer fires," said Mr Burns, the Joint Management Coordinator with the QYAC.

The team stressed that large old trees are ecologically important and hold cultural significance for Indigenous peoples, but their protection is often overlooked.

ANSTO environmental change scientist Dr Quan Hua explained that radiocarbon dating using the wood coring method on live trees is challenging because of difficulty in locating the pith, wood at the centre of a stem, the oldest part of the tree.

"Growth rings are inconsistent in trees in sub-tropical Australia, and it has been found that estimating tree ages based on growth increments tended to overestimate their age," he said.

There are other challenges because of hollow cavities, asymmetry in trees and the potential for contamination during corings.

"Using a single recent sample for dating will yield an imprecise calendar age consisting of several possible age ranges between 1650 and 1950, which is due to large fluctuations in atmospheric radiocarbon in this period," said Dr Hua.

"But dating samples at several depths along the core provides not only a chronological constraint for the dates and consequently more precise estimates, but also better approach for locating the pith." he said.

The research included a revised estimate of dates previously published based on single samples, where there was a variation.

Samples from other species, including smooth-barked apple, forest red gum, pink bloodwood and scribbly gum were also studied and dated.

The oldest tree studied was a smooth-barked apple with an age range of 430-531 years at a 95% confidence level.

Griffith University also collaborated on the research.