What is the Way to tell the Age of a Tree?

Telling the age of trees can be a fascinating exercise – and there are a number of ways to work out their longevity. The simplest way is to cut the tree down and then count the interior concentric rings within the trunk. There will be one ring for every year of the tree’s life.   

But hang on a minute. If the only reason for cutting the tree down is to establish how old it is, then what a tragic waste of a beautiful specimen, which might otherwise have enjoyed many hundreds of years of uninterrupted growth.

Alternatively, you could carry out a core boring to discover the ring numbers.  Once again, however, this could cause an immense amount of damage to the tree.

The truth is that you don’t need to chop a tree down or bore into it, to identify its lifespan.    

The kindest way to determine a tree’s age

There is a non-invasive alternative to estimate (with reasonable accuracy) the age of a tree. You start by measuring the girth of the trunk, or the circumference, approximately five feet (150 cm) from the ground.

You then need to do a small calculation, according to the type of tree. This is because different species grow at different rates. In the UK, a tree’s average annual growth rate around the girth is 2.5cm. This ‘middle of the road’ figure would apply to the likes of ash, beech, elm and hazel.  Pine, spruce and sycamore can increase either side of 3cm a year, whilst slower growers, like oak and yew, expand in girth size by about 1.88cm and 1.25 cm annually.  

So, depending on the species, divide the circumference by the annual growth rate. A calculator could come in handy at this point!   

As an example, if you measure an oak tree with a girth of 100 cm and then divide that by 1.88 cm (its annual growth) you would be able to calculate the age as 53.2 years. Similarly, an elm with a circumference of 150 cm, would be about 60 years old (120 divided by 2.5).

When you see some of these magnificent old oak trees, if you could find one with a girth measuring 900 cm, you could say, with reasonable accuracy, that   it would have begun life during the reign of Henry VIII. Of course, there are plenty of specimens that date back even further than that. Tape measures to the ready!