500-year-old mangrove tree in Hunter Wetlands National Park at Fullerton Cove examined in University of Newcastle project, as Dr Danielle Verdon-Kidd and Matthew Goodwin get to root of climate history

The tree, in Hunter Wetlands National Park at Fullerton Cove, is giving researchers a rare glimpse of the past.

Dr Danielle Verdon-Kidd, of the University of Newcastle, said existing climate records were "quite short".

"Because of this, we really know very little about the real flood and drought history of the region," Dr Verdon-Kidd said.

The project is being done for Matthew Goodwin's PhD.

"We found a tree that we've dated to 500 years old, from the mid 1500s," Mr Goodwin said.

"The main stem was rotten in the centre, but it had about five large branches.

"It was only through a core in one of the branches that we were able to get to the centre and work out its age."

He said the tree is "extremely rare".

"I know of a few other examples where researchers have dated mangroves to maybe 800 or 1200 years old, but they were not living trees."

Dr Verdon-Kidd, a climate extremes scientist, said "we were hoping the tree would be pre-colonial".

She was delighted to know the tree was there at the same time the local Indigenous community lived around that area.

"That history is really relevant and interesting."

The tree was not easy to find. Mr Goodwin had to trek and kayak through wetlands.

"I covered a lot of that area on foot, trying to find the biggest, oldest trees."

Finding a tree with an adequate core was not easy, as mangroves tend to rot in the centre.

"You'll often find one that's big enough, but 99 per cent of them are rotten in the centre," he said. "It's very rare to find one where you can take a core from the centre of the tree that's still intact."

The trees have secrets within.

"We can interpret stories in the wood," Mr Goodwin said.

This can provide information to help plan for extreme climate events in the future.

"It's fascinating to look back into the past and see what was happening and for that to be useful for the decisions we make now.

"We've been getting these huge droughts and floods and we have very little idea how often they happen and how extreme they can get over the long term"

Dr Verdon-Kidd said the mangroves will "give us a better idea of what sort of floods and droughts we can expect under Australia's climate".

"The mangroves have their feet in the water," she said.

"So they're perfectly positioned to tell us whether there was a lot of rainfall or a drought because they're sucking that water up."

That water had properties that can give insight into whether it was a wet or dry year and when the tree was growing.

A tree corer is used to take mangrove samples. "We core into the tree and get a sample that's narrower than a pencil. Then we can see the layers within," she said.

The chemical properties of the layers contain climate data from the past.

"The tree rings can tell us the history of the Hunter wetland flows and the rainfall in the region," she said.

The researchers are also examining stalagmites from the Wombeyan Caves [south of the Blue Mountains] to get a 2000-year history of NSW.

"Within the stalagmites, there are layers. The chemical and physical properties in those can tell us about what the climate has been like over that time."

Dr Verdon-Kidd said settler's diaries had revealed there was a major drought from 1790 to 1793, known as the "Settlement Drought".

"We are keen to see how that drought compares to recent droughts we have experienced.

"Likewise, we are interested to see how long extended wet periods like the one we are experiencing now can last."

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