Girth of oak

Following from reference 1, back at the end of June, I have been taking an interest in how one might determine the age of a tree from its girth, a rather less intrusive procedure than boring a hole in it or chopping it down. And a good deal less bother than poking around in local records for a date of birth. The method I have been looking at is that at reference 2. The relevant tree was a Scots pine near the bottom of West Hill, on the way into Epsom.

In the course of this, I came across an oak tree of known age, on Clay Hill Green, on the top of West Hill, as noticed at reference 3. Including the snap included there above. Image reference: 20260623_213129.

A tree planted to commemorate Chuter Ede who died in 1965, so planted in 1965 or shortly thereafter, making it of the order of 60 years old. What did not occur to me at the time was that this was well short of 'mature', according to reference 2.

I measured the girth, with the aid of a length of string and my walking stick, at 227cm, some little while ago, took some identification snaps of the leaves - what sort of an oak was it? - a little while after that and have now got around to doing something with them.

Identification

I knew the tree was an oak, but given that it makes a difference what sort of oak, I had better try and pin that one down too. And, at this time of year, maybe leaves were the best bet. So I started Google Images (GI) on the snap above. Without logging in to my account, so on the free tier.

He goes for English Oak, aka the Pedunculate Oak, aka Quercus robur. Pedunculate as the acorns have stalks. He also tells me that there are more clues at the base of the leaf, in particular the near absence of stalk.

It so happens that I had some more detailed leaf snaps, and offer him this one.

He now changes his mind and goes for Sessile Oak, aka Quercus petraea. Sessile for the acorns not having stalks, not that this is much help just presently. He also tells me that the stalks of the leaves are 1-2cm in length.

I then suggest that: 'I would have thought that these petioles are more like 1 to 2mm than 1 to 2cm'. He changes his mind again, reverting to English oak. He says something about being so busy looking at the shapes of the bases of the leaves, he got the scale wrong and so got the length of the leaf stalks wrong. Which does not sound terribly clever, but I think we have got to the right answer.

Just to wrap things up, I feed him the image at the top of this post and tell him about it being a commemorative tree. He gets quite eloquent on this topic: presumably there is plenty of text out there on the Internet for him to chew on. Text is what he does best.

Girth

I then turn my attention back to reference 2, going so far as to print off a copy of the worksheet that comes with it.

The basis of the model is that a tree lays down new growth, just underneath the bark, throughout its life: the radius and hence the girth of the tree increase steadily through life, with no growth meaning no life. In temperate zones with seasons, this is apt to result in growth rings, with the number of rings being, more or less, the age of the tree. This model attempts to age a tree from its girth, to which end it describes the life of a tree in three stages: youth, maturity and old-age, with different rules applying to the growth rings at each stage.

At this point, it dawns on me that I don't have a mature tree at all. Table 1a - which anyway conflates English oak and sessile oak, suggests that maturity - in the model's sense - is in the range 70 to 120 years, with my take being that 100 would be fair for this rather dry site, on top of a hill. In any event, more than the less than 60 years we have for my tree. So I only need consider the first stage.

The model also makes the simplifying assumption that age rings are of roughly equal thickness - despite the increasing radius - until the tree is mature and the canopy is complete, after which they decline in a regular way, with radius (and girth). A canopy of more or less fixed size can only produce so much wood a year.

Which means that Table 1a gives me a ring width of the order of 3.5mm on a radius of 35cm., which suggests to me an age of 100 years - although you can get this down to 70 years if you promote the tree to a candidate champion. Hmmm.

Conclusions

It seems likely that calculations of this sort are subject to a good deal of variation, with an analysis of girth by height - which I grant is not what we are doing here - showing a good scatter . Wrong tree too - 120 odd large Scots pines from all over the British Isles - but I dare say a analysis of the right tree would not look that different.

Maybe estimating age from girth is just not a very reliable business, the best efforts of reference 2 notwithstanding - but as noted above, it is easy and it is not intrusive; one is not damaging the tree by measuring it.

Work in progress. Maybe reference 7 will be helpful.

PS 1: I am getting the impression that there are a lot of tree huggers out there. I am not alone!

PS 2: 20260804 supplementary. I have now got around to girthing the twin pines at the top of West Hill, at the start of Meadway. Probably planted at or around the time of the building of the Chase Estate, mainly between the wars. There is also a memorial arch. The western one looks much bigger than the eastern one, but their girths are much the same at 204cm and 186cm respectively.

I wonder about the bark, thick and rugged on these trees, but I did not find any adjustment for bark at reference 2. Maybe White wanted to keep things as simple as possible.

The base of the eastern tree is snapped above, illustrating both the bark and my wheeze for using the walking stick to hold one end of the string while one walks the other end around the tree. A simple overhand knot serves to mark the spot until one gets home.

References

Reference 1: https://psmv6.blogspot.com/2026/06/early-and-late.html.

Reference 2: Estimating the age of large and veteran trees in Britain – John White, Forestry Commission – 1998. 

Reference 3: https://psmv6.blogspot.com/2026/07/two-circuits.html.

Reference 4: https://www.treeguideuk.co.uk/oaks/. Some useful stuff to be found here.

Reference 5: https://www.treeregister.org/. And here.

Reference 6: https://psmv5.blogspot.com/2025/11/memory-lane.html. Another excursion into the world of champion trees. A rather smaller one, with pears rather than acorns; pears not much bigger than acorns as it happens.

Reference 7: Estimating the age of groups of trees in historic landscapes – Ben Lennon – 2012.