Where are Britain's oldest trees?

In the churchyard at Fortingall in Perthshire stands a yew that Forestry and Land Scotland reckon is 5,000 years old. Other estimates are a more modest 2,000 to 3,000 years. Nobody really knows, because the heart of a hollow yew has long since rotted away and with it the rings you would need to count. When its girth was measured in 1771 it was 56 feet round, about 17.1 metres.

Britain is unusually rich in very old trees, partly because so much of its landscape was kept as deer park, royal forest, wood pasture and churchyard for centuries. But where exactly are they? The best inventory, the Woodland Trust's Ancient Tree Inventory, is not open for reuse, so I have not used it. Instead I asked what the open data know: OpenStreetMap, the volunteer map of the world, plus Wikidata and Wikipedia. The answer is part natural history and part portrait of the people who map trees.

01 · The mapBritain's notable trees, as the open map knows them

Each dot is a notable tree in OpenStreetMap, coloured by species where the mapper recorded one and sized by its girth where a credible girth is tagged. Dark rings mark trees with a sign of great age. Stars are eight famous ancient trees described on Wikipedia. Search for a town or village to see the nearest notable trees, or tap a dot.

02 · Mappers, not treesA map of enthusiasm

My extract of OpenStreetMap holds 70,394 trees in the United Kingdom with a name, girth, age or similar tag. Almost all of them, 65,827, are street and park trees imported from council surveys with an age class such as "mature" or "young". Only 1,626 pass my filter for a notable tree. Of these, 716 have a name, 239 are tagged as a natural monument, 656 as a landmark and 139 have a credible girth of 3 m or more.

The pattern is lumpy in a way that real trees are not. 42% of all the notable trees fall in just ten 10 km squares of the National Grid, and the busiest single square, around Hood Green near Barnsley, holds 158. That is not a Yorkshire forest of giants: 158 unnamed trees of unrecorded species in Barnsley are tagged as "landmarks", as are 121 in Northumberland. In Coventry, 59 unnamed trees carry the natural monument tag. Across Britain, 655 notable trees (40%) are unnamed trees of unknown species flagged in this way: the habits of a handful of mappers.

Wales, home to some of Britain's most famous yews, has just 27 notable trees on the open map; Scotland has 92 and Northern Ireland 10, against 1,497 in England. And even the stars are patchy: of the 90 trees in Wikidata described as remarkable or heritage trees in the UK, I could find 48 (53%) on OpenStreetMap within 150 m of the Wikidata point. The famous Llangernyw Yew in Conwy, which Wikipedia says may be over 4,000 years old, does not appear as a named tree in my extract at all.

The open map of old trees is a map of enthusiasm: it shows where people have gone out to look.

03 · Which treesMostly oaks

Only 579 of the notable trees (36%) have a species, either tagged or plain from their name ("the Wortley Oak"). Among those, the oak dominates: 273 trees, 47% of the known total, and 51% of the known-species trees with a sign of great age.

Oaks are the classic old tree of English parks and hedgerows, and they include the biggest girths on the map: the Queen Elizabeth Oak near Lodsworth in West Sussex is tagged at 13.18 m round, and Majesty, the Fredville Oak in Kent, at 12.36 m. Next to them stands a sweet chestnut, the Cowdray Colossus, at 12.5 m. The second most common group of old-looking trees is a surprise: 40 giant redwoods, 28 of them with a girth of 3 m or more or a monument tag. They are big, but they are newcomers from California, planted in parks and estates from the nineteenth century onwards; a large girth is not the same thing as great age.

04 · Churchyard yewsThe trees by the church door

Yews are different. Of the 176 yews anywhere in my OpenStreetMap extract, 32 (18%) stand within 50 m of a mapped church or chapel. For every other kind of tree the figure is 1.3%. A yew is 13.7 times as likely as other trees to be in or by a churchyard. Among the notable yews the link is stronger still: 21 of 32 (66%).

The churchyard yews belong to the old parish churches, not to the chapels. Of the 32 yews by a church, 28 are nearest an Anglican, Church in Wales or Catholic church and only 2 nearest a Methodist, Baptist or other chapel, although chapels make up 12,316 of the 38,811 places of worship on the map. Why yews and churches go together is an old argument: shelter, symbolism, a pre-Christian sacred site taken over by the church. These data cannot settle it. But they do show that, on the open map at least, old yews are found where the ground has been a churchyard for a very long time.

Five of the six famous ancient yews I list from Wikipedia (Fortingall, Llangernyw, Crowhurst, Ashbrittle and Defynnog) are in churchyards. Wales stands out, if only faintly in the open data: 7 of its 3,121 mapped places of worship have a mapped yew within 50 m, 2.2 per thousand, against 0.6 per thousand in England. These are tiny numbers, and they say more about how few yews are mapped than about how many grow.

05 · Royal forestsHunting grounds and their giants

After 1066 the Norman kings put great tracts of land under forest law to protect deer and the "vert", the greenery that fed them. At the height of the system, Wikipedia notes, a third of southern England was royal forest. A forest was a legal zone, not necessarily a wood, but where land stayed as wood pasture and park for centuries, trees could grow old. Wikidata gives a point for 38 former royal forests in Britain. Circles of 5 km round those points cover 1.3% of the land.

Those circles hold 3.3% of the notable trees and 4.7% of the trees with a sign of great age, about 3.5 times their share of the land. That is 13 trees, so it is a hint rather than a finding, and 9 of the 13 are in just two places. In Savernake Forest in Wiltshire, a royal forest that is still a forest, three mapped oaks are among the biggest girths on the open map: the Big Belly Oak (11.18 m), the King of Limbs (10.8 m) and the Cathedral Oak (10.4 m). In the New Forest stand the Knightwood Oak and a group of giant redwoods. The Major Oak in Sherwood Forest, which Wikipedia reports was found to have died in 2026, is on the map too.

Deer parks, the private hunting enclosures of medieval lords, should be just as rich in old trees. But only 76 areas named as deer parks are drawn in OpenStreetMap, covering 66.9 km², and just 3 notable trees fall inside them. That is a gap in the map, not in the landscape.

06 · How old?What girth can and cannot tell you

The only safe way to age a tree is to count its rings, and the oldest trees are usually hollow. Foresters use girth instead. Alan Mitchell's rule of thumb is that a tree with a full crown, growing in the open, adds about 2.5 cm (an inch) of girth a year, measured at 1.5 m above the ground. By that rule, a girth of 3 m means about 120 years, 5 m about 200 and 10 m about 400. Wikipedia's article on veteran trees suggests 3 m at 1.5 m as one rough test for a veteran.

Only 150 notable trees carry a girth I trust, and 10 of them measure 10 m or more. The rule of thumb is a good start for a tree a few centuries old. For the truly ancient it fails badly, because old trees slow down, lose their crowns and hollow out. Set the girths Wikipedia gives for famous trees against the ages it reports and the gap is enormous.

By Mitchell's rule the Llangernyw Yew, 10.75 m round at ground level, would be about 430 years old; the churchyard certificate says 4,000 to 5,000. The Major Oak, 10.06 m round in 1999, comes out at about 402 years, against the 800 to 1,200 usually quoted. A big girth tells you a tree is old. It cannot tell you how old, and for yews it barely tells you anything beyond "very".

07 · LimitsWhat this can and cannot show

The map shows mappers. Nearly everything here depends on who has mapped trees and how they tagged them. Counts by region measure enthusiasm as much as trees. The Woodland Trust's Ancient Tree Inventory and the Tree Register hold far richer records, but the Inventory is not open for reuse, so it is not used here.

Tags are inconsistent. "Landmark" and "natural monument" mean different things to different mappers, 1,498 girth tags in my extract are survey defaults repeated across whole streets, and 2,391 trees have any girth at all. My credibility rules remove the worst values but cannot check a measurement.

Churchyards and forests are approximations. A tree within 50 m of the centre of a church is usually in or beside its churchyard, but not always. Royal forest circles round a single Wikidata point are a crude stand-in for forest boundaries that changed over centuries.

Ages are estimates. Mitchell's rule is a rule of thumb. Woodland trees grow more slowly, young trees faster, and ancient trees much more slowly. Wikipedia's ages for famous trees are themselves disputed ranges.