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The Lost Generation of Ancient Trees

At around 1,100 years old, and almost 11m in girth, the Big Belly Oak is the oldest tree in Savernake Forest in south-west England. A tiny sapling at the Battle of Hastings in 1066, Big Belly Oak has lived through the War of the Roses, the Black Death, the English Civil War, the Industrial Revolution and two world wars. Now gnarled and knobbly, Big Belly Oak’s trunk is strapped up with a metal girdle to keep it from falling apart.

The ancients of Savernake Forest are something of an anomaly in the wider landscape. A thousand years ago, Savernake was wood-pasture grazed with livestock. Then from the 12th century it was a royal hunting forest with woodland, coppice, common land and small farms. In the 20th century, that picture changed dramatically. Worldwide over a third of primary forests — ones that have been undisturbed by humans for over 140 years — were cut down between 1900 and 2015. The loss is attributed to land-use change like the creation of farms or housing developments, and tree harvesting for wood. In Britain, although the canopy cover grew throughout the 20th century, most of this new growth was down to planting new saplings — the country has lost almost half of its ancient woodland since the 1930s.

The way we manage forests has changed, explains Paul Rutter, woodland advisor for Plantlife and project officer at Ancients of the Future. The intensification of agriculture has meant the removal of many hedgerows and trees that grow within them, as fields have been made larger. Traditional forest management practices have largely been replaced by plantation forestry and whole-tree extraction. Ancient trees are becoming smothered by overcrowded canopies, saplings, shrubs and brambles. Many have been felled for timber or urban development. Add to that an increase in tree diseases and the challenges of climate change. The result is that fewer trees are surviving — or being allowed to grow — into their old age.

“In the tree world everything happens slowly,” says Rutter. “We call it tree time.”

Trees reach their ancient phase of life at different ages. For beech this is from 225 years old, oaks from 400 years and yew 900 years. During this phase the trunk hollows, holes and cavities appear and deadwood reaches above the living canopy.

It can take up to 300 years before heart-rot, the decay at the centre of an ageing tree, is established enough that insects can start moving in and laying their larvae, says Rutter. “It becomes a complex ecosystem. The ancient trees that we have today, ones that are 300–900 years old — perhaps older — support an incredibly wide range of species.”

Take oaks, which can live for more than 1,000 years and grow to more than 10 m in girth. A recent study found that oaks native to Great Britain support 2,300 other species, of which 326 are completely dependent on them. The flower and leaf buds are eaten by caterpillars of purple hairstreak butterflies and holes provide nesting spots for the pied flycatcher, redstart and marsh tit.

In autumn, mammals like squirrels, badgers and deer feed on the acorns. The leaves fall to the ground and form a rich leaf mould where invertebrates including stag beetles and fungi such as the oak bug milkcap thrive. The resident insects, in turn, are a vital food source for many birds and bats.

So, what can we do differently to ensure we never see a generational gap like this again? The Ancient Tree Forum offers land owners advice on how to care for their ancient trees — putting up barriers to protect them from livestock, clearing nearby vegetation that is competing for light, creating a root protection zone and propping up heavy limbs or bracing ageing trunks.

The Woodland Trust calls for full legal protection for all ancient trees to prevent further loss, and enforcement of government urban development policies that prevent encroachment on ancient woodlands.