This question has perplexed yew research for centuries. It remains unanswered, because the truth is, we do not know. However, studies carried out in Britain in the last 25 years have resulted in a clearer picture beginning to emerge than ever before. We will look at this later. In the meantime, it is worth investigating the history behind the modern science of dendrochronology (tree ring dating).
The Swiss botanist Augustin Pyramus de Candolle (1778 -1841) was one of the first to realise growth rates and estimated ages of yews could be ascertained from measuring the girth (circumference of the trunk) and counting annual growth rings in the diameter and radius. Unfortunately, of course, this science can only best be done if a yew has been felled or otherwise fallen victim to natural circumstances, storm damage for example, and allows exposed rings to be counted. If no ring count is available, measuring the girth (and calculating diameter and radius) and estimating growth rates is the next best thing.
However, it is often not possible to get a measuring tape tight around the trunk of a yew unlike other trees such as oak, beech or pine due to the fluted form of many yews, which crates lobate growth in cross section. A tape around such a yew means it can only touch the outer limits of the lobes and there are gaps devoid of surface wood in the measurement. In cross section, unlike having fairly concentric rings as most trees grow year after year, a yew can have different ring counts extending from the pith at the centre to the bark depending on which direction the count was taken. Rings can also appear and then disappear – these are known as ghost rings. Even in a small cross section of a branch, the growth patterns can be far from anything like concentric.
De Candolle’s discoveries concluded yews were capable of extremely slow growth and proposed that whatever the oldest tree in Europe was, it would probably be a yew and in that he was right. He also claimed to have found yews in Britain of 2000 years old and more. However, when his work was subjected to later scrutiny in the 19th century it was not approved by everyone, with John Eddowes Bowman (1785 – 1841) commenting De Candolle made:
“Young trees too old and old trees too young” (1)
Bowman himself believed yews could reach vast ages. He mainly agreed with De Candolle’s methods, but his own work was later heavily criticised by John Lowe (1830 – 1902) author of the classic The Yew-trees of Great Britain and Ireland (Macmillan 1897) who said that Bowman’s work was of no use at all. In Chapter 12 of Lowe’s book, Notes, he investigates yews all over Britain, including sites famous in his day in Scotland including Fortingall, Inchlonaig, Dryburgh Abbey and Finlaystone House, to name a few. Much attention is given to analysing measurements taken by himself and others both in and before his time in attempts to extrapolate a reliable growth rate formula from the data i.e. x number of rings in inches in a diameter or radius. Many examples give wildly contradictory results. In general, he is quite dismissive of many claims that certain yews are particularly old or ancient and he regards 3000 years a rare, and absolute, maximum.
Regarding the Fortingall yew, Lowe highlights a discrepancy of four feet in girth when first measured by Daines Barrington and Thomas Pennant in 1769 who recorded 52 feet (1560 cm) and 56 feet (1680 cm) respectively. He then quotes Sir Robert Christison (1797-1882) the famous toxicologist, regarding this discrepancy:
“Of this tree, Sir R. Christison rightly observes: ‘It is not easy to satisfy oneself merely from the superannuated remains as they now stand that they belong to what was once one tree only’. There can be no doubt on this subject, and the outline sketch he gives strongly supports this idea. ‘Little information as to its rate of growth is to be got from sections of the yew itself. On many parts of the shell and the branch, the rates varied from one inch (2.5 cm) in 48 to one in 60, 68, 70, and 90 years. None of these rates could be reasonably taken as denoting the growth of the trunk for more than its last hundred years of life. It is better…to use the general rules arrived at, according to which the tree in the first place is assumed to have attained a girth of 22 feet (660 cm) in a thousand years. After that age no information yet got warrants a rate of more than one inch (circumference) in thirty five years. Take then the lowest measurement (Barrington’s) at 52 feet (1560 cm) the difference will thus add 2000 years to the age of the Fortingall yew, making it in all 3000 years.” (3)
The biggest problem yews present to dendrochronology is that many yews over 400 years of age have begun to hollow. This process is induced by a fungus and causes cubic rot in the heartwood and is part of a natural regeneration process which can take centuries to complete.
As the hollowing process continues, often at the same time aerial roots can emerge growing from the interior of the shell. These reach the ground and take root, gradually thickening in the hollow and there are many examples of yews with interior trunk stems, some of which have reached a girth of 4 feet (120 cm).
A hollow yew obviously means there are no rings to count. Trying to ascertain the age of a hollow yew from growth rates taken from the shell or a branch is also unreliable. As noted earlier, the Fortingall yew has shown that annual growth rates can be widely variable and inconsistent and is not the only example by far discovered in yew research. Suffice to say, a partial ring count will only show what the growth rate has been in the part of the yew the sample came from. Normally it cannot reliably be extrapolated to apply to the rest of the yew.
A further factor to consider is that yews grow according to their specific individual circumstances. Avenues of yews planted at the same time in what are apparently identical conditions can show girths within a range of 200 cm – 400 cm, showing it is difficult to predict how any individual yew will grow the more centuries that pass. Yews with similar girths of 350 cm have been found to vary in age between 300 – 800 years because of specific habitat factors. Some yews in extreme environments in Britain e.g. upon steep hills, mountains, cliffs, escarpments and river valleys have been identified as amongst the slowest growing woody plants in the world. One example, taken from a branch was found to be generating rings a single cell in thickness (2). This is imperceptible to the eye without using microscopes. If a yew increases in girth only by a few inches or centimetres per year then over the course of an average human lifetime it would appear to not grow at all. This has indeed led to some yews apparently maintaining the same girth for centuries.
Yews have always presented a conundrum to anyone who has tried to accurately predict the age of a yew without the benefit of a ring count from the circumference to the core. A century after the comments of John Lowe nothing had changed. Throughout the 20th century the opinions of how old a yew could be remained without a consensus. In the 1990’s the book The Sacred Yew claimed that yews could exceed 3,000 years old and proposed some yews in Britain could be 5,000 years old. By the end of the decade, opinions on how old the Fortingall Yew could be ranged from 2,000 – 9,000 years old (4).
In 2004 and again in 2011, with more refined techniques of dendrochronology, it was found that the famous Borrowdale Yews in Cumbria, England were 1500 years old. By a continuous ring count from a yew of six feet (180 cm) girth growing on a cliff at Lllangollen in Wales, an age of 1,000 years was proven. By these examples we now know that yews outside churchyards can definitely live to be over 1,000 years old with 1,500 years the current limit so far found in Britain. This is not to say that 1,500 years old is a limit for the lifetime of a yew in Britain, only that it is the limit found so far. It may well be breached as further research continues. Whether it may reach 2,000 years or much more only time will tell.
We will never know how many yews have been lost to deforestation and climate change in the last 8,000 years in Britain. There may have been yews which were well over 2,000 years old and perhaps 3,000 years or more. Yews growing in mountain environments in Turkey, known as ‘monumental’ yews because of their huge size, are thought to be survivors of deforestation during the period of the Roman Empire and some are claimed to be 3,000 years old. There was ring count evidence for this but unfortunately it was lost in a fire before it could be scrutinised by dendrochronologists from outside Turkey. However, the high mountainous environment where they grow is very different to any yew habitat found in Britain and has produced yews three times the height of a typical British yew, which usually have a maximum height of around 40 – 50 ft. (15 metres). But that is not to say that post glacial Britain never witnessed yews of that age here, just that if it did, most probably none are left today.
Perhaps there may have been some over 1,000 years ago, because in the prose of the ninth century author Nennius (who allegedly wrote The History of the Britons around 828) we find the following:
“The lives of three wattles [chickens}, the life of a hound,
The lives of three hounds, the life of a steed,
The lives of three steeds, the life of a man,
The lives of three eagles, the life of a yew,
The life of a yew, the length of an age
Seven ages from creation to doom.”
It is not apparent what timespan is meant by Nennius when he uses the term of an ‘age’. Perhaps this may refer to what was then regarded as an ‘age’. This was the time taken to transition from one sign of the Zodiac to another in what is known as the Precession of the Equinoxes e.g. the transition from the Age of Aries to Pisces occurred around 2,000 years ago and will next enter the Age of Aquarius. This process takes approximately 2,160 years to move from one sign into another and if Nennius was referring to an astrological age, then the ‘life’ of a yew according to him would be 2160 years which is compelling to consider.
The reason why it is compelling is the latest research upon the rollercoaster of trying to formulate what age a yew is when applied to yews with large girths (24 ft or 7 metres plus) has downgraded what where thought to be yews of 2,000 years and more, many of which were listed in The Sacred Yew. This happened due to a radical new look at measuring yews and resolving the problems presented in taking girth measurements as outlined earlier (5).
The research also seems to suggest that only the most exceptional yews living today, a handful in all of Britain, are more than 2,000 years old. Many in churchyards claimed to be 3,000 years old and over are more like 1,600 and linked to the earliest Christian sites established in south west England and Wales.
In other words, few yews in Britain today have lived the ‘life of an age’. But it is one of the greatest wonders of nature, indeed of life of Earth, that yew trees can, if left in peace to fulfil their lives as Nature intends and fulfil the words of Nennius as fact rather than poetic licence.
We may be closer than ever in accurately understanding how old the oldest yews in Britain may be, but that does not mean yews typically have finite lifespans. The number of post glacial yews in Britain lost over the millennia is an unknown factor. And there is nothing which can discount that Britain may have witnessed yews of truly vast ages which are now lost. In the words of the late Allen Mitchell founder of the Tree Register of Great Britain and Ireland there is no real reason why a yew should ever die. If not a victim to catastrophe or extreme habitat change or human action, in theory a yew can survive ‘forever’ by constantly regenerating itself and we know the many ways yews can do this. They deserve their legendary status as being an ‘eternal’ and ‘immortal’ tree full of ‘divine’ life not subject to the usual rules of mortality for most life on Earth.
To answer how old can a yew tree become perhaps means putting a slight twist on the question as the answer is not necessarily measured in years, but rather a timescale we cannot truly imagine.
References
- Robert Bevan Jones: The Ancient Yew (3rd edition) Windgather Press 2017
- Doug Larsen : Cliff Ecology: Pattern and Process in Cliff Ecosystems, Cambridge University Press, 2003
- Lowe, John: pps. 210 – 211, Notes, The Yew-trees of Great Britain and Ireland, Macmillan 1897
- //heraldscotland.com/news/12334383.bellamy-seeking-an-ancient-answer
- Finding ages for large specimens of Taxus Baccata – https://www.ancient-yew.org/s.php/finding-ages-for-large-specimens-of-taxus-baccata/3/88
