Hollow tree trunks: what are they good for?

If there’s one way to get close to nature, it’s stepping inside a giant hollow tree. But why do trees hollow out and what are the benefits?

Stand inside an ancient tree and you are standing inside a piece of history. Their hollow centres have even housed dinner parties, preacher’s pulpits and bullpens. It’s said that the centre of Lincolnshire's Bowthorpe Oak once held 39 people within its trunk!

Why do trunks become hollow?

A hollowing trunk is a natural process and not necessarily a sign of an ailing tree. The centre of the tree is deadwood which is slowly decayed by fungi. The fungi is perfectly happy in the deadwood and will rarely touch the living sapwood. 

Trees spend years storing up minerals in the wood in the centre of the trunk. As this wood is decayed, the minerals are released and can be used once more by the tree. Along with the yearly supply of leaves and any decaying branches, the hollowing trunk is providing the tree with recycled nutrients, helping it to live longer. 

A hollow trunk might react better in high winds too, allowing the tree to bend and reduce damage. 

Who lives in the hollows? 

Hollow trunks are ideal homes for a lot of wildlife. There’s protection from extreme weather and the temperature will be much more constant than outside. 

A hollowing trunk can provide a nesting or roost site for bats and birds. At the foot of the trunk, cavernous spaces are perfect for hedgehogs to hibernate or snakes to lay their eggs. Lots of fungi, epiphytes and invertebrates will also colonise a hollowing tree.

Famous hollow trees

• The Borrowdale Yews, Cumbria, were celebrated by Wordsworth in his 1803 poem, Yew Trees. The largest yew is over seven metres in girth and can hold four people. 
• The Marten Oak, Cheshire, was referred to as the largest tree in England in 1880. It has served as a bullpen, a pigsty and a Wendy house over the years. 
• The Crowhurst Yew, Surrey, is a churchyard tree with a door built into the trunk to guard its hollow centre. In 1850 it housed a table and benches.
• The Pulpit Yew, Denbighshire, North Wales is home to an outdoor lectern. Steps lead through the hollow of the tree up to a raised seat and podium where legend has it that John Wesley, founder of Methodism once preached.

Help protect ancient trees 

The UK has thousands of ancient trees - volunteers have recorded over 209,000 for the Ancient Tree Inventory. Our oldest trees, some over a thousand years old, are important to our heritage and wildlife, yet they don't have the protection they need. It’s time for this to change - and you can help. 

We're calling for strong, consistent laws and policies that value and protect our oldest and most important trees – a system similar to that for listed buildings or ancient monuments. Sign our petition calling for governments across the UK to protect our living legends.