Britain's mightiest oak: A staggering 1,046 years old, it's still going strong (even if it is getting a bit stout around the middle) 

Blenheim Palace in Oxfordshire is most famous as the birthplace of Winston Churchill and home of the Dukes of Marlborough.

It now has another claim to fame — new research has discovered its woodland is home to the greatest collection of ancient oak trees in Europe.

At least 60 of the oaks in Blenheim’s High Park have been dated back to the Middle Ages. And experts from the Ancient Tree Forum have estimated the age of one of them at 1,046 years old — probably the oldest oak in Britain.

The latest measurement, made four weeks ago, means the oak started growing in AD970, a century before the Norman Conquest. It was more than 500 years old at the Battle of Bosworth and 700 years old when the first Duke of Marlborough began to build Blenheim in 1705.

In fact, it’s impossible to put an exact date on this great OAP of the woods. Like most ancient oaks, its trunk has hollowed out over centuries, meaning you could no longer count its rings, even if you were to do the unthinkable and chop it down.

Instead, the experts did the next best thing, which was to measure its enormous girth and come up with a circumference of ten metres. Comparing that with the girth of other trees with known planting dates, the experts came up with that 1,046-year figure.

‘Before, we thought our oldest oak was the King Oak, a 925-year-old tree nearby, which is more than nine metres in circumference,’ says Roy Cox, Blenheim’s rural enterprises manager.

‘We have known for some time that Blenheim Palace is home to one of the greatest collections of oak trees in Europe. But, as we gain a better understanding of the woodland, it continues to reveal new secrets.’

The great oak is showing signs of age. One of its lowest branches has collapsed, but it is still clinging on to the tree, stretching out at a horizontal angle.

Where the oak has had to take the strain of the enormous branches, it has built up a thickly ridged layer of compressed bark underneath, like the swelling muscle on an arm.

At some dramatic moment centuries ago, the oak’s trunk split in two, but both halves kept on growing. You can look into the void where its heart has been hollowed out over the decades.

Today, a bug trap hangs in that void, catching some of the 50 different types of beetle and 16 butterfly and moth species that flourish in this ancient wildwood.

In fact, each oak — especially such an ancient one as this — is the living heart of an extraordinary eco-system.

Blenheim Palace is home to one of the greatest collections of oak trees in Europe 

Oaks provide an astonishingly rich habitat that supports more life forms than any other native tree. Up to 280 species of insect alone live on an English oak — and these, in turn, supply many birds with a food source. The trees also play host to small mammals, such as dormice, and birds, such as tawny owls.

Crevices in the bark can provide nesting spots for birds, while bats might roost in holes in the trunk, where they can dine on the insects that flourish there.

Acorns are poisonous to horses, cattle and sheep because of the tannic and gallic acids found in them, which can cause severe damage to the gastrointestinal system and kidneys.

Yet in the autumn, acorns provide an important food source for badgers and deer, who are not affected in the same way.

On the tree itself, a pecking order has developed, with the larvae of the ichneumon wasp feeding on the pupae of the oak moth caterpillar.

The oak moth in turn eats the oak leaves. The older the oak, the better for those beetles that feed off the dead wood in its heart.

The larvae of the stag beetle, the biggest beetle in the UK, rely on dead oak to feed on. Fungi, too, live on oak roots and, in turn, the roots take nutrients and water from the fungi, in a mutually beneficial way.

Flower and leaf buds of the English oak, meanwhile, are the food plants of the caterpillars of purple hairstreak butterflies. Other wildlife recorded at Blenheim’s High Park include otters, water voles, ospreys, lizards, grass snakes and great crested newts. In spring, the forest floor is carpeted with bluebells.

Like ageing humans, the ancient oak has got shorter in old age as its crown has ‘retrenched’, or reduced in size. ‘It starts to shrink and loses its outer limbs,’ says Roy Cox. ‘It goes back to its minimal form.’

Again, like many humans, the tree has grown fatter and more squat, building up extra bulges of timber at its base to support the gangly mass of branches above.

The rule of thumb for ancient oaks is that they grow for 300 years, mature for another 300 years and then ‘veteranise’, or decay, for another 300. And this king of the forest just keeps on veteranising, without dying. According to the Ancient Tree Forum, there is no precise age that makes a tree ancient. It depends on the species and other factors, including the site where it grows.

Over half of the ancient oaks of the world are in England 

A birch would be considered ancient at 150 years old. Yews, which can live for thousands of years, are defined as ancient at 800. Oaks are called ancient when they hit 400.

But, still, this old boy is pushing out new growth. A slim branch, only around a century old, reaches out 4 ft off the ground.

The canopy of leaves is so thick it’s hard to see the sky overhead. And, every year, the tree still produces hundreds of potential offspring in the shape of acorns. (Oaks reach their acorn-producing prime at 50 years old, when they become ‘sexually mature’, though they can produce acorns as young as five.)

What a wonder of nature it is, as it sits alone, on its own commanding hillock, buried deep in the wood, far from the 750,000 tourists who visit Blenheim Palace every year.

Visitors can walk on a designated path through the wood and view the ancient trees — which are 90 per cent oak, with some beeches scattered around.

Sadly, they won’t be able to access this most exceptional of trees. The oak must be kept out of bounds to preserve its habitat — an official Site of Special Scientific Interest, visited once a year when it is surveyed by the estate forestry team.

The tree has its own GPS tag and a tiny metal plate on its trunk, identifying it with a unique number. It is an extraordinary piece of luck that it has survived for all those centuries, while so much of the rest of the country was deforested.

In the 18th century, the wood was going to be felled for ship-building, but the first Duke of Marlborough intervened to stop it happening.

In the 12th century, when the oak was already more than a century old, the area was part of Henry I’s deer park.

It remained a hunting ground for centuries and the woodland is still used by the Duke of Marlborough for shooting game. Fallow and roe deer skip through the forest, but are no longer hunted.

Another stroke of luck came the oak’s way when the wood was incorporated into the first Duke of Marlborough’s estate more than 300 years ago. As part of a vast estate — 12,000 acres today — High Park could be treated as treasured woodland rather than a commercial forest to be harvested.

By the time Capability Brown, our greatest landscape gardener, came to design Blenheim’s park in 1763, he realised High Park was too precious to destroy or remodel.

Instead, the wood was kept in its natural form and could be seen in all its ancient wildness from the palace.

So the oak lived on — and may well continue to for centuries. Even when it finally, sadly, dies, its neighbours — the 700-year-old youngsters next to the 925-year-old King Oak — will take their positions among Britain’s oldest trees.

It also helped that the oak happened to grow up in this country.

‘Over half of the ancient oaks of the world are in England,’ says Mr Cox. ‘This island is so important to the world’s collection of trees.’

In the whole of England, there are thought to be 115 ancient oaks. In the rest of the world, including Wales and Scotland, there are only 93. This is partly thanks to our damp, temperate climate, partly thanks to our soil. Blenheim’s soil is clay on a foundation of Cotswold stone.

The survival of the great, ancient oak is also to do with our taste for trees and sympathetically managed woodland — a taste that the Blenheim oak can only encourage.

‘There’s an element of pride at finding this tree at Blenheim Palace,’ says Mr Cox. ‘But we also have a responsibility to future generations to preserve such an important woodland and to get the public out of town to enjoy such a lovely area.’

What a chance in a million. A 1,000-year-old oak saved by the royal love of hunting, a ducal estate and the English adoration of trees.