While humans are all too familiar with the ravages of getting older, many trees seem to handle ageing a lot better.

Certain trees can live for thousands of years and appear to be immortal.

But not everyone is convinced these old timers can escape death due to old age.

Regardless, could humans with their relatively puny lifespans have something to learn from these ancient trees? Some scientists think so.

Establishing how old the oldest living tree is depends a bit on which plants are in the running for the title.

You could argue that Australia's Wollemi pine, which has been cloning itself for more than 60 million years, deserves the title. But that's kind of cheating because this involves multiple stems growing from the one rootstock.

This is why the oldest tree in the world is generally regarded as a single-stemmed bristlecone pine called Pinus longaeva.

This species can live to around 5,000 years and does well where most other plants cannot even grow in rocky, dry, high-altitude areas in the United States.

What's amazing is that scientists have not so far been able to show that getting older directly affects the health of such millennial trees, plant biologist Sergi Munne-Bosch from the University of Barcelona says.

It's because of this, some say these trees are essentially immortal.

But in a recent article, Professor Munne-Bosch argues that it's likely even ancient trees could die from old age assuming something else doesn't kill them first.

He emphasises that there's a difference between ageing, which is about how long an organism has lived, and age-related deterioration, which is referred to as senescence.

"Just because we can't track senescence in long-lived trees doesn't mean they are immortal."

Professor Munne-Bosch points to recent research on centuries-old Ginkgo biloba trees that found no evidence of senescence.

The study was the first to look for evidence of age-related changes in cells of the cambium, a layer just beneath the bark that contains cells that can produce new tissue throughout the plant's life.

It confirmed the long-lived trees, which in this case were up to 667 years old, were just as healthy as younger ones says Professor Munne-Bosch.

"They grow very well, they produce seeds, they produce flowers, so they are healthy."

He points out that even though a 667-year-old tree seems old when compared to a human, it is relatively young for a ginkgo.

"This species can live for more than two millennia."

Professor Munne-Bosch argues that the ginkgo researchers' data shows that older trees had thinner vascular tissue and that this hints at possible age-related deterioration that would be more obvious in even older trees.

Yet despite this deterioration, he says these trees are more likely to die from insects, disease, fire, drought or loggers, than old age.

"For a species that can live for millennia, aging is not really a problem in evolutionary terms because they are much more likely to die of something else."

The problem is there are so few of these long-lived trees that it's hard to get the data to know for certain whether they can die of old age.

"We cannot prove it either way," Professor Munne-Bosch says, adding that age-related deterioration is likely to happen in these trees at such a different pace compared to in humans.

"For a Ginkgo biloba, six centuries is not as physiologically relevant as it is to us."

Brenda Casper, a professor of biology at the University of Pennsylvania says it's not clear that the changes found in the older Ginkgo biloba trees were necessarily detrimental to the tree.

But she agrees the low number of millennial trees makes it hard to study their longevity.

"It's difficult to find statistical evidence for senescence."

Even if there were enough trees, she says some of the age-related deterioration may be hard to detect, or we may not know what to look for.

"It's not just internal physiology per se but it's the interaction of the tree with its environment."

For example, she says it would be hard to measure whether age had made a tree more susceptible to disease, or less structurally sound so it's more likely to fall over in a windstorm.

Even if the jury is out on whether millennial trees are immortal, some experts say their longevity could be inspirational for medical research.

Professor Munne-Bosch says such trees can draw on a bag of tricks to help them "postpone death".

First is having a simple body plan with modular-like branches and roots. This means they can compartmentalise any damaged or dead roots or branches and work around them.

"They can lose part of leaves or roots and continue to be healthy..

And he says although 95 per cent of the trunk of a tree might be dead, the living cambium just beneath the bark is "one of the secrets of longevity" in trees.

Millennial trees have used the combination of these features to their best advantage and Professor Munne-Bosch says these tricks are providing a model for scientists researching the negative effects of ageing.

"Imagine if we could regenerate our lungs or circulatory system every year, we would be much healthier than we are."

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Professor of biomedical engineering at the University of New South Wales, Melissa Knothe Tate is one researcher who is inspired by millennial trees.

"They have units and if one unit breaks you can replace it with another unit."

Only a small percentage of an individual long-lived tree may be alive, but she argues it's all about survival of the cells that are able to regenerate the tree.

"Those that survive best, survive longest."

"Millennial trees are the best survivors because they've seen a lot."

While a tree and a human might seem worlds apart, Professor Knothe Tate sees the similarities, pointing to the role of stem cells in maintaining bones in humans.

She says cells add new layers to bone, like tree rings, to increase girth and when bone is injured, stem cells quickly help repair it.

"We're constantly renewing our bones and trees do something similar."

Professor Knothe Tate says she is using stem cells and new biomaterials that emulate tree cambium, to create replacement tissue in the lab, and has several patents for the work.

"I think about plants a lot when I'm up in the mountains and amongst the trees."

Professor Knothe Tate, who draws on her training in philosophy, biology and mechanical engineering for her work, sees other similarities that can inspire research.

For example, she likens the human brain to the network of roots and branches that helps a tree remain resilient if one part is damaged, another part can sometimes take up the slack.

"As parts of the brain are injured or die, it's remarkable what functionality we can retain,

"If we knew which of the brain's networks were essential for certain functions, we may be able to grow them."

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Professor Knothe Tate also set up a science education project for girls that explores the parallels between the biomechanics of trees and bones. It was inspired by her observation of how huge trees sway like a blade of grass in the wind.

She has high hopes for the potential of regenerative medicine research that draws on knowledge from other disciplines like plant biology.

"Then we can then start to think about making ourselves immortal."

Plant biologist Professor Munne-Bosch is also enthusiastic.

"The future of medicine is very similar to what has evolved in millennial trees."

But while regenerating tissues will help humans live much longer, he doubts we will ever be immortal.

"It won't be forever, because we are more likely to die of something else, whether it be an accident or a pandemic."

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Are very long-lived trees immortal and what can they teach humans? - ABC News