Another lesson about ageing trees

Clive Humphreys

Clive is the Tree Warden for Oundle and a key member of the team organising Rockingham Forest Vision’s latest project the Ancient Tree Hunt.

Here he describes what he has learned about ways of telling the age of a tree and muses about what "a life well lived" might mean for trees.

I have recently had another great lesson on the wonder of trees. I was privileged to be part of a meeting with our RFV group who are organising and promoting the Ancient Tree Inventory for our area. The invited guest was David Alderman who is the Head Verifier for the Ancient Tree Inventory Team, and one of our aims was to discuss what makes a notable, veteran or ancient tree and ways of assessing age other than by its girth.

This is where it gets interesting and more analogistic - but I must emphasise, this is a musing on my behalf!

If I were an oak tree standing in parkland, planted as a specimen, with as much sunlight as I can gather, as much water as I can use, free of all competition from others around me, then I would get bigger. In much the same way as a human might if given access to as much (or more) food and drink as they wanted or needed. Free from hinderance or harsh words, they would also gain girth over the years!

As described by Alan Mitchell’s formula, an oak tree in parkland has a growth rate of approximately 2.5 centimetres a year to its girth, whereas a woodland tree maybe only gains 1.5 centimetres. A tree in a wood, or if you want, a human in a crowd ,has to compete for space and nutrients to grow, so it gains rather less girth.

My point and what is now becoming a recognised problem to ageing a tree, is that girth alone is not a reliable indicator of age. Of course it goes a long way to establishing something near, but it is not conclusive. If we then add in factors such as the species' life expectancy, elevation, geographic location etc, the established charts for aging start to become unreliable.

How do we look at trees for ageing? We should perhaps be looking at the tree for other indicators of age, in the same philosophic way as we could (but shouldn’t) ‘judge’ humans. Have they led a life well lived? Do the trees carry the scars of a life spent in competition and hard work helping the environment they inhabit and of which they are a vital part. Have branches been damaged, broken off and died? Is the bark split and hollowed, allowing disease and rot to begin? Is the tree a home for insects, the hollows nesting places for birds? Do the diseased parts have moss and fungi growing in and on them. Is the heart wood dying?

If we look for these things, which can only happen over many years, then a tree can be identified as a veteran or perhaps an ancient, even though it may not necessarily have the girth of a parkland tree, many of which can incidentally also be a ‘notable’ because of their position and cultural significance to a community.

I think all this is really Interesting, isn’t it?

Then we need to look into how different species vary. A very old Hawthorn will not have the girth of an Oak or Beech but it could be as old. The thing they will all have in common are the scars or indicators of a ‘life well lived’. For example, the Oak trees in the ‘cloud forests’ on the West Coast of Scotland  grow very slowly, twisted and gnarled, battered by winds and cold rain, covered with very slow growing mosses and lichen, which are incidentally good indicators of age, but the trees have a very small girth. So they could be much older than those in southern-counties parkland.

My lesson -  we must look at a tree in more ways than just size. Has it been significant in its habitat? Has it contributed to the environment around it? Of course it is very easily argued that every tree does just that but if we are trying to age a specimen then we have to observe more details.

Thank you for indulging me with my rambling, actual and metaphorical, as we go on this journey and I must add these thoughts are my own and that I hold no researched qualification.