Are trees certain to die of old age? Or could they live forever?

‘TREES are immortal’. 

A great theory to explore following the recent major storms we have experienced on Ireland. The loss to our already heavily-deforested landscape has been severe. 

Recently I was reminded of this idea by a social media post where a large eucalyptus in San Francisco had failed, crashing down onto moving cars on a nearby road, luckily injuring no-one.

Local news reports centred around how this “ageing tree”, with suspected root decay, had simply fallen over, despite measurements of the fallen tree indicating this euc was only 80 years old. 

There was comment that many other similar aged euc trees in that area would have to be removed due to safety concerns.

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However, we know this species and other trees can live a lot longer than that. 
Eucalyptus regularly achieve ages involving hundreds of years, species of Taxus, like our Irish Yew, are known to reach longevities into the thousands of years, as do the Bristlecone pine trees from Nevada in the USA, with one member of its species thought to be the oldest tree currently alive on Earth (at a staggering 5,065 years old).

We often hear people talk about trees as having a shelf life, seemingly needing to be removed due to their age or the size they have achieved. But is this a good way to rationalise whether action is needed or not? 

So, the theory: “Trees don’t die due to age, they succumb to external influences. Essentially, they are killed.” 

Now, as a man who has spent much of his adult life killing trees (don’t be too hard on me, there’s almost always been a sound reason and I’ve definitely planted more than I’ve sent to the gallows) the topic of immortality in trees is as important to me as the need to be able to read and discuss trees accurately.

Older trees can fail in a multitude of ways; from infection to windthrow, human involvement (like machinery compaction or felling for timber), fire, flood, insect predation, even what we could consider suicide. (Dutch elm disease death is a response by infected trees, where they effectively plug up their transport tubes, stopping the movement of nutrients and water, starving themselves, which eventually causes their own death.)

A large Ginkgo tree, Ginkgo biloba, with spectacular yellow and gold autumnal colours. (Image: Getty)

There was a fantastic essay published by two Italian scientists in a 2020 issue of the New Phytologist journal that grabbed my attention.

They stated: “Published evidence suggests that trees do not die because of genetically programmed senescence in their meristems, but rather are killed by an external agent or a disturbance event.”

Their take on this topic made me think, yeah, trees don’t necessarily have defined lifespans ... and I can’t say things like: “Beech trees only live for X hundred years, then they need to be felled.”

Trees persist where they are allowed to, and fail due to describable factors. My mind was blown by this essay. 

Considering there exists no evidence that, as trees persist, destructive genetic mutations pile up, nor can we say trees lose their ability to produce new tissue over time. Both these facts are not exactly adequate explanation to conclude immortality.

Let’s look at the longest-lived Bristlecone pines for a moment. The environment they are from could be described as harsh, and certainly they can kill trees.

Yet, many of the longest lived of this species persist in these tough conditions, mountainous rocky thin soil.

One of the Italian scientists described this so: “It is as if trees that live a long time, up to thousands of years, abide by the axiom, that which doesn’t kill you makes you stronger.”

Other scientists have studied the Ginkgo biloba tree to better understand their development and potential for immortality. Many people wrongly assume that all trees slow down growth in a gradual fashion as they age – the Ginkgo demonstrates that is not true.

By taking samples of trees at varying ages and assessing their annual increment rings, researchers found that these trees can actually speed up growth as they develop. To add to that, this species displays evidence that photosynthetic ability, leaf area size, and seed quality don’t differ with age.

Testing was done on a genetic level on cambial tissue from Ginkgo ranging from three to 667 years of age. From memory, these tests went some way to demonstrate there was little change in gene expression between the young and older trees. 

I’ve heard other people state that trees change over time, which is obviously true. Some tree species seem to experience less vigour as they age, they appear to lose ability to continue productive growth.

Is this a sign of ageing, or rather a sign of some external limitation?

Either way, trees fascinate many of us, they provide a range of important ecosystem services to not only ourselves but to other animal and plant species too, and the broader environment. It’s almost unimaginable that we will outlive them. 

Ancient trees are winners; they are the champions who have persisted. We should identify them, learn about them, and engage in their promotion.

Sitka spruce, Northern Ireland’s current tallest recorded tree, measured via tape drop by A. Doran, A. Domarkas, and D. Hamill. (Image: eA/Dave Hamill)

When we arborists go about our business of advising tree owners on the best course of action, maybe we should all refrain from using the phrases “end of life cycle” or “that tree’s getting too old”.

One of my favourite replies to customers solely concerned with tree age is: “They can get a lot older.” 

We could try our best to retain old and ancient trees where possible, we could pass on quality information about trees and the issues that impact them, choosing to veteranise or remove only as a last option.

What is certain is that we have a lot more to learn about trees, about the way we discuss them, and how they are viewed by society.