World's oldest trees are not immortal but 'ageing very slowly'

World’s oldest trees are NOT immortal but have ways to reduce the wear and tear of ageing over thousands of years, scientist says

  • Biologist reveals that signs of trees ageing are almost imperceptible to people 
  • However this does not mean that they’re immortal despite being 5,000 years old
  • Trees’ hormonal changes eventually lead to mechanical constraints and death 
  • Ancient trees are of interest to biologists as they can reveal secrets of a long life

The world’s oldest trees are not immortal, but just ageing very slowly, a plant biologist has concluded in a new report. 

The oldest trees on Earth have stood for nearly 5,000 years and have therefore appeared to hold great promise that some organisms on this planet are eternal. 

Biologists have long-wondered to what extent these ancient organisms undergo senescence – the process of physically deteriorating as they age. 

But although signs of senescence in long-lived trees may be almost imperceptible to people, this does not mean that they’re immortal, a plant scientist claims. 

Inevitable hormonal changes eventually leads to mechanical constraints and death, he says, pointing to a recent study of ginkgoes, one of the world’s longest-lived trees.

Ginkgoes, one of the world’s longest-lived trees, display age-related reductions in the contents of auxin, a plant hormone produced in the stem tip that promotes cell elongation

‘The measure of time is something that we have invented as humans, and to a millennial tree, it does not matter at all,’ said plant biologist Professor Sergi Munné-Bosch at the University of Barcelona, who details tree mortality in a new research paper.

‘When we try to study these organisms, we’re really astonished that they live so long, but this doesn’t mean that they’re immortal. 

‘They live so long because they have many mechanisms to reduce a lot of the wear and tear of ageing.’   

The idea of becoming immortal has always been extremely attractive to humans, Munné-Bosch says. 

Long-lived trees have received special attention in the study of ageing, as ‘a sort of mirror’ in which we could potentially see ourselves reflected in our efforts to achieve greater longevity. 

Trees have a variety of ways to reduce their chances of death from ageing, including ‘building life on death’ by growing new shoots from trunks composed of 90 per cent non-living biomass. 

Indeed, long-lived trees, such as ginkgoes and bristlecone pines, are mostly formed of dead tissue, especially when they grow old. 

The capacity of the vascular cambium – the main growth tissue in the stems and roots of plants – to resume growth each year allows life to be built around ‘a sea’ of dead plant mass.

The capacity of the vascular cambium to resume growth each year allows life to be built around a sea of dead organic mass, making trees exceptional long-lived organisms at the limits of life and death

But despite their well-evolved methods to prolonging the ageing process, they still undergo physiological stress associated with senescence, which will ultimately prevent immortality. 

‘They have limits – there are physical and mechanical constraints that limit their ability to live indefinitely,’ said Munné-Bosch.  

The oldest individual tree in the world is thought to be in the US, where a Great Basin bristlecone pine in California’s White Mountains has been aged at more than 5,000 years.

A Fortingall Yew in Perthshire, Scotland, is believed to be the oldest tree in the UK, meanwhile, with an estimated age between 2,000 and 3,000 years, according to the Woodland Trust. 

The famous yew tree in the churchyard of the village of Fortingall in highland Perthshire. The tree is thought to be around 3,000 to 5,000 years old

Tress can be aged by measuring their girth – specifically the rings that develop over time that increase that girth. 

But because of their extreme lifespans, the effects of ageing over time must be studied at a somewhat impossible timescale.  

To see the real-time effects of ageing on long-lived trees, scientists would have to conduct studies that last hundreds if not thousands of years. 

Little is known about what the process of senescence looks like in trees, and also finding enough trees with a lifespan of several thousands of years to find similarities can be challenging. 

‘When a species of tree can live for five millennia, it’s very difficult to find even two trees that are between two and five millennia,’ said Munné-Bosch. 

A study published earlier this year in the journal Proceedings of the National Academy of Sciences said one species of ginkgo – G. biloba – may ‘escape senescence at the whole-plant level’.

However, Munné-Bosch reports in his research paper that ginkgoes display age-related reductions in the contents of auxin, a plant hormone produced in the stem tip that promotes cell elongation.   

Ginkgoes (C) and bristlecone pines (D), are mostly formed of dead tissue, especially when they grow old

These findings fit in with reduced cell division and expansion capacity, eventually leading to mechanical constraints and death.    

For old trees, dying of senescence is a possibility, but the probability of dying from other causes, such as disease, is significantly higher. 

‘They don’t have to worry about senescence because they have other things that worry them more,’ Munné-Bosch said. 

Studying the ways trees prolong senescence is important as research conducted in trees and long-lived plant species can inform other disciplines.

For example, aspects of regenerative medicine are based on mechanisms that have already evolved in trees.

Professor Munné-Bosch has published his research paper in the journal Trends in Plant Science. 

WHAT CAN TREE RINGS TELL US? 

Trees can live for hundreds—and sometimes even thousands—of years. 

Over this long lifetime, a tree can experience a variety of environmental conditions: wet years, dry years, cold years, hot years, early frosts, forest fires and more. 

Concentric rings in tree trunks tell us how old the tree is, and what the weather was like during each year of the tree’s life. 

The light-coloured rings represent wood that grew in the spring and early summer, while the dark rings represent wood that grew in the late summer and fall. One light ring plus one dark ring equals one year of the tree’s life.

Because trees are sensitive to local climate conditions, such as rain and temperature, they give scientists some information about that area’s local climate in the past.

Concentric rings in tree trunks tell us how old the tree is, and what the weather was like during each year of the tree’s life. One light ring plus one dark ring equals one year of the tree’s life

 For example, tree rings usually grow wider in warm, wet years and they are thinner in years when it is cold and dry.

 If the tree has experienced stressful conditions, such as a drought, the tree might hardly grow at all in those years.

Very old trees can offer clues about what the climate was like long before measurements were recorded. This field—the study of past climates—is called paleoclimatology.

Paleoclimatologists rely upon natural sources of climate data, such as tree rings, cores drilled from Antarctic ice and sediment collected from the bottom of lakes and oceans. These sources, called proxies, can extend our knowledge of weather and climate from hundreds to millions of years 

Combined with weather and climate information from satellites, they can help scientists model major climate events that shaped our planet in the past. 

And these models can also help us make predictions about what climate patterns to expect in the future. 

 SOURCE: NASA

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