The expression "farmers are the original environmentalists" gets thrown around a lot in regional Queensland.

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Key points: Carbon dating has estimated a grey mangrove tree on a Queensland cattle station is 738 years old

Carbon dating has estimated a grey mangrove tree on a Queensland cattle station is 738 years old An ecologist says it's the oldest known mangrove in Australia and probably the world

An ecologist says it's the oldest known mangrove in Australia and probably the world Until recently, it was believed the grey mangrove, a common species on coastal mainland Australia, lived for up to 200 years

The expression refers to the ecological management skills those working the land have and how if they mistreat it, they are putting themselves out of a job.

Queensland cattle farmer Lindsay Titmarsh proves that behind every saying there is some truth.

The Titmarsh family has worked the nearly 5,000-hectare Tandora property, just north of Maryborough in south-east Queensland, since 1907.

From the homestead you look over vast scrubland and mangrove forest across the Mary River estuary towards the world's largest sand island K'gari (Fraser Island), which translates from the Indigenous Butchulla language as "paradise".

Mr Titmarsh tends to the vast property with the same care and attention as a cottage garden might receive.

Mr Titmarsh has extensive knowledge of the trees on his property. ( ABC Wide Bay: Brad Marsellos )

He could walk you around the farm for days telling stories about the animals and plants that cohabit with his family and he has even published several books about the region.

But of the thousands of trees on Tandora Station, a certain grey mangrove, or Avicennia marina, caught Mr Titmarsh's eye and he instantly knew there was something special about it.

The Magna Carta tree

Mr Titmarsh first noticed the tree when he was walking through the area 20 years ago.

"Before that all we were doing was chasing crabs or pigs in here and the mangroves were a bit of a nuisance when you were chasing a pig, so it's only in the last 20 years I have looked at them from a different angle and seen the beauty of them," he said.

"When I saw this tree I knew it was old, it was the oldest one I have ever seen."

The old grey mangrove caught Mr Titmarsh's eye about two decades ago. ( ABC Wide Bay: Brad Marsellos )

Eventually Mr Titmarsh decided he would have the tree carbon dated and sourced a sample from inside the hollow base, which he sent to the New Zealand University of Waikato Radiocarbon Dating Laboratory.

The results came back as 738 +/- 65 BP meaning the mangrove tree was more than 700 years old.

"When I found out how old it was I named it the Magna Carta tree because if you go back that far you get to the year 1215, which was Magna Carta days," Mr Titmarsh said.

"It's still alive and it's even still got fruit on it."

Mr Titmarsh took a sample from inside the mangrove tree to have carbon dated. ( ABC Wide Bay: Brad Marsellos )

Oldest known mangrove in Australia

Professor Norman Duke is a mangrove ecologist and botanist who has named about 10 per cent of the world's mangrove population in his 40 years of study.

"This is the oldest [mangrove] tree we know about in Australia and probably the world ranking in that respect," Professor Duke said.

"We've got a few people shooting in pictures from the Philippines and other places looking to compete with that but nobody else has carbon dated and confirmed it.

"When Lindsay Titmarsh has carbon dated and confirmed it, that's pretty special."

New growth on the base of the old mangrove tree. ( ABC Wide Bay: Brad Marsellos )

Generally, the base diameter of a mangrove tree is an indicator of its age and Professor Duke said the measurement of the Magna Carta tree stem matched the carbon dating.

"The age matches with the girth or stem, which is a proxy of a measure to determine their age," he said.

"That tree measures around three metres and that matches with what we have for the determination of age of other trees and we develop relationships on a graph that shows age versus stem diameter.

"So with all the evidence we have, it's perfectly justified to trust that carbon dating."

While the tree is currently the oldest Avicennia marina on record in Australia and most likely the world, there could be older mangroves yet to be found.

Mr Titmarsh has a strong connection with the land. ( ABC Wide Bay: Brad Marsellos )

Surviving extreme conditions

Of the 46 mangrove species currently found in Australia, Avicennia marina is a common mangrove located all over the coastal mainland.

Until recently, it was believed they lived for only 100 or 200 years, Professor Duke said.

While other types of trees can live for thousands of years, mangroves thrive in extreme conditions, making them susceptible to floods, storms and tidal or sea level changes, affecting their lifespan.

The mangrove still fruits after all these years. ( ABC Wide Bay: Brad Marsellos )

"There's a tree called a Bristlecone pine that lives over tens of thousands of years and even the Huon pine in Tasmania hangs in there, they are survivors," Professor Duke said.

"These [mangrove] trees are real survivors too but there are limits, as discovered in the Gulf of Carpentaria recently, where 8,000 hectares of mangroves, the same species as this old tree, died in a one or two month period in 2015 just because of a temporary drop in sea level," Professor Duke said.

When the Magna Carta tree began life it was at the low tide mark but with the Mary River changing its course, the tree now only just sits in the intertidal zone that mangroves require to stay alive.

The small grove it belongs to has managed to avoid the wrath of cyclones or fire.

Mary River's pristine mangroves

Mangrove forests are vital to Australia's ecosystem and are protected by law for the role they play as a nursery for marine wildlife, a filter system for land run-off, buffer from erosion and as a carbon resource.

The Mary River region has been described as a pristine mangrove environment and Mr Titmarsh wants to make sure it stays that way.

"We've got 10 varieties of mangroves in the Mary and Susan River estuary, as you go north you've got more and as you go south you've got less," Mr Titmarsh said.

"Some have roots that come out of the ground, some extrude salt through their leaves, you can lick pristine salt off, they are all so different.

Mr Titmarsh feels strongly about protecting the mangroves on his property. ( ABC: Eliza Rogers )

"The Mary River mangroves are pristine, they are not all stuffed up like [in] Gladstone and around the place and we are getting more of them, we have more mudbanks then we have ever had, so we have more mangroves than we have ever had."

While Mr Titmarsh is passionate about all the mangroves on his property, as he stands beside the tree he has named the Magna Carta, you can tell this one is close to his heart.

"See that little tree sprouting over there? In 800 years he will be like this one," Mr Titmarsh said.

"This mangrove tree is special, it's history."