Logo

Why Bother Ageing a Tree?

Walk any ancient British wood and you will meet trees that have outlived every person who planted them, and quite possibly the language they spoke. Our folklore is full of them: the fairy thorn that must never be cut, the gospel oak marking a parish boundary, the ash beside the well where wishes were tied. Knowing roughly how old such a tree is changes the way you stand beside it. It also sharpens your eye as a naturalist and makes your nature journal far richer than a list of species names.

You do not need to harm the tree to get a decent answer. Three clues — girth, branch whorls and bark — will give you a working estimate. Only a core sample gives certainty, and we shall come to that at the end.

The Girth Tape Method

The oldest trick in the woodman's book is also the simplest. Measure the trunk's circumference, then divide by an average annual growth rate for that species.

Measure at roughly 1.4 metres above ground — chest height, easy to repeat on the same tree year after year. On a slope, take the measurement from the uphill side so you are always measuring the same point. If the trunk forks below that height, measure the narrowest point just beneath the fork and note it down. A flexible fabric tape is best; failing that, wrap a length of string around the trunk, mark it, and measure the string against a ruler at home.

Growth rates vary hugely with soil, light and competition, but these are fair British averages in centimetres of circumference per year:

• Oak: about 2, slower on poor or ancient sites
• Ash: about 2.5, faster when young
• Beech and sycamore: around 2.5
• Birch: about 2 in youth, slowing with age
• Scots pine: roughly 1.5 to 2
• Willow: around 3

So a hedgerow oak of 200 centimetres girth is likely a century old. A parkland oak of 500 centimetres may be 250 years — or far more, if it has grown slowly in old pasture. Treat the answer as a range, not a fact.

Counting Whorls on Conifers

Many conifers give you their age outright. Scots pine, spruce, fir and larch push out one ring, or whorl, of branches each year from the leading shoot. Find the topmost whorl and count downwards, ring by ring, like the rungs of a ladder. Add one for the current year's growth at the tip.

The complication is that mature conifers shed their lower branches, so the oldest whorls have vanished along with the dead stubs. Count what remains on the living trunk, then estimate the missing years by dividing the length of bare, branch-free trunk by the average annual height growth for the site — perhaps 30 to 40 centimetres on good lowland ground, far less on exposed moorland. It is rough, but it stops you underestimating a fine old pine by fifty years.

Reading Bark, Crown and Habitat

Bark is the least reliable clue and the most enjoyable to learn. Young oaks are smooth and grey-green, often dusted with lichen; mature ones develop deep fissures and plates; the very old grow burrs, lose their crown centre and hollow out. Birch bark is white and papery with dark diamond-shaped lenticels, but the base of an old birch turns dark and rugged. Ash stays smooth and pale in youth and later shows interlacing ridges like the back of an old hand. Willow is ridged and heavy from quite early on.

Then there is the great exception: beech bark stays smooth for two hundred years and more, which is exactly why no one ages a beech on bark alone. Learn a few exceptions like this and you will avoid the commonest mistake in the woods.

Look also at the crown. A stag-headed oak, its upper limbs dead and bare above a spreading frame, is almost certainly a veteran. Fungi help too: beefsteak fungus on an oak, or a broad shelf of bracket fungus, suggests heartwood decay and a tree of real age. A hollow trunk is a clue to centuries, not a sign of death — many of our oldest trees are hollow and thriving, and the cavity is home to bats, owls and a whole community of beetles.

Keeping a Nature Journal Record

An estimate written nowhere is an estimate lost. Set aside a page for each tree you visit regularly, and record:

• The date, the place and the weather
• The species, and the girth at 1.4 metres
• Whorl count, if a conifer, or bark notes, if broadleaf
• A quick pencil sketch of the bark pattern and the tree's silhouette
• Your estimate as a range, plus how confident you feel and why

A wax crayon rubbing of bark takes seconds and captures texture better than words. If you can, measure the same tree each year; the small annual increase tells you far more than any single reading. This is where woodland folklore and careful observation meet — the story of a tree, told by you.

Where Certainty Lies

For a true age, an increment borer is the only answer. This is a hollow auger that removes a pencil-thin core of wood from bark to pith, leaving the tree unharmed; you count the growth rings, then plug the hole. It takes a trained hand, the landowner's permission, and a good reason. For most of us, in most woods, a tape, a notebook and a patient eye are enough.

And here is the craftsman's caution: knowing a tree's age should make you gentler with it, not quicker to cut it. Work with coppice regrowth, windfall and deadwood where you can, and leave the veterans — the hollow, stag-headed, lichen-crusted giants — to their own slow business. They have earned it.