Rooted to the ground since years BC

I GOT INTO an argument with someone the other day about the life expectancy of trees.

Many tree lovers seem to want to believe that trees can live longer than the scientists say they can and there is a lot of misinformation on the subject.

A recent book on trees suggests that Robin Hood and his Merry Men feasted under the Major Oak in Sherwood Forest in England and that the same tree is still growing there today.

Robin Hood, if he existed at all, lived in the reign of Richard I about 620 or 630 years ago and oak trees don’t live that long — at least, under normal circumstances. I’ll come to the abnormal circumstances in a minute.

Charles II is supposed to have hidden from Cromwell’s men after his defeat at the Battle of Worcester in a tree called the Boscobel Oak that is still living. That was in 1651. This is possible but unlikely. Oaks occasionally reach 350 to 400 years old, but surely the king would not have chosen a very young tree to hide in.

Yew trees are another story. For some reason there don’t seem to be any very old yew trees in Ireland but there are some extremely ancient ones in Britain.

When King John was called to account by his barons in 1215 he signed the Magna Carta (Great Charter) beneath an ancient yew tree at Runnymede on the banks of the Thames. The river has altered its course in the meantime but it is almost certain that the same tree is still growing in Runnymede.

A harder story to prove is that of a yew tree in Scotland with a plaque suggesting that the young Pontius Pilate sat in its shade ‘and wondered what the future held’. It’s not impossible. Pontius Pilate’s father was a Roman soldier garrisoned in Britain and yew trees can certainly exceed 2,000 years of age, possibly 4,000.

BUT these are the exceptions. Many Irish tree species only live for about the same length of time as Irish people, or a little bit longer. A birch or hazel of 100 is a very old tree and 120 is about the maximum, under normal circumstances.

I’d better explain what I mean by ‘normal circumstances’. A peculiarity of trees is that stress increases their life expectancy, completely opposite to what medical people tell us about humans. This effect was first noticed among trees that are coppiced or pollarded. This is a process where trees are continuously cut for a crop of timber and then allowed to grow again from the stump.

In coppicing, the tree is cut more or less at ground level and in pollarding it’s cut above the browse line of animals at a couple of metres above the ground. The stress that this causes the tree prolongs its life and, if the process is regularly and correctly done, may give it the potential to become immortal.

So, under normal circumstances oaks live no longer than 400 years, but there are pollard oaks in England’s Windsor Great Park that are 800 years old. And coppice stools of hazel have been scientifically measured at 900 years old.

Stress can also occur from natural causes. Probably the oldest trees in the world are bristlecone pines growing in California and Nevada that are between 4,000 and 4,500 years old. They grow at an altitude of over 3000 metres in desert conditions and so are very stressed.

In Ireland, the oldest trees are not the great parkland specimens but stunted little things growing in cracks in the rock or on windswept bogs.

dick.warner@examiner.ie

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