Scientists are drilling into the bark of trees that have survived for hundreds of years to discover the secrets that lie beneath.

A new study has found some of the coolabahs and river red gums that stand in the Gwydir Wetlands in northern NSW are 500 years old.

Researchers from the NSW Department of Climate Change, Energy, the Environment and Water (DCCEEW) and the University of Newcastle have used a combination of dendrochronology and radiocarbon “bomb-pulse” dating to analyse the age and growth history of floodplain eucalypts.

Kathryn Taffs, from the DCCEEW’s surface water science team, said the oldest tree so far analysed was a coolabah with a diameter of 176 centimetres. 

Some trees in the Gwydir Wetlands are estimated to be hundreds of years old. (Supplied: DCCEEW)

“This is a really old, very magnificent tree … dated to be 566 years old, so what a matriarch for the community,” Dr Taffs said.

“That was really outstanding that it’s been surviving on that floodplain for five centuries.”

Dr Taffs said the species had been considered too complex for reliable aging.

“Eucalypt wood is really tough, and this technique, what it does, it takes a reinforced steel core about the size of a pencil and we attach it to a drill and drill it into the trunk of a tree,” she said.

“It doesn’t harm them in any way, and what we end up with is … a pencil-sized slither from that tree that we can then analyse.”

The study looks at how previous drought and flooding events have affected the wetlands. (Supplied: DCCEEW)

The key findings

While the age of the coolabah and red river gums is significant, the research has also revealed previously unknown climate history affecting the Gwydir Wetlands.

Ms Taffs said the growth ring patterns revealed past droughts, floods and water availability.

“We’re very interested in how this can inform our management of water and one thing we’ve already found is the reproduction of the trees isn’t a regular cycle,” she said.

“We’ve found that there’ve been six pulses where the trees have been able to successfully produce seeds, that seed germinates into saplings and the saplings grow up into mature trees.”

One of the study’s findings is that coolabahs and river red gums can live for 500 years in the Gwydir Wetlands. (Supplied: DCCEEW)

Dr Taffs said those “pulses” resulted in sudden, large influxes of new trees called “mass recruitment events”.

She said the research showed pulses in the 1500s, 1600s, 1800s and early 1900s corresponding to major environmental and hydrological changes.

“We now know it’s really important to deliver water onto these floodplains to support those trees maturing and being able to reproduce in the next pulse,” Dr Taffs said.

University of Newcastle climate scientist Danielle Verdon-Kidd said the importance of the research should not be underestimated.

“This groundbreaking project has shown that floodplain eucalypts hold tremendous potential for understanding past climate and water conditions in parts of Australia where long-term records don’t exist,” Associate Professor Verdon-Kidd said.

Coolabahs and river red gums are a common sight across the wetlands. (Supplied: DCCEEW)

Richard Kingsford AO, director of Centre for Ecosystem Science at UNSW in Sydney, said while he was aware of similar research in other areas with red river gums, he had not seen it done with coolabahs.

Professor Kingsford said the research could have beneficial impacts for other wetland areas. 

“It’s potentially really exciting because one of the things that’s difficult to understand is where the systems have come from in terms of their flooding and their history,” Professor Kingsford said.

“I think one of the things we’re always trying to understand is what is the natural rhythm of a river … so being able to reconstruct that history tells us so much.”

Environmental water impact

The results of the study will form part of the NSW government’s Environmental Outcomes Monitoring and Research Program report.

Dr Taffs said the project could pave the way for similar studies across other major river systems and contribute to conversations about environmental water management.

Changes in water flows and climate have helped alter Gwydir floodplains over hundreds of years. (Supplied: DCCEEW)

“We really want to tease apart what these mature floodplain trees’ water needs are throughout all of its lifecycle to make sure the delivery of environmental water occurs to support that community to survive into the future,” she said.