Hollow Trees – Risks & Benefits

  • By: The DIG for Kids
  • Time to read: 5 min.

It’s like something out of a fairytale when you come across a hollow tree. I recently saw one that had been fitted with a door and every time we’ve driven past it, I’ve told my daughter that an elf lives there. 

But moving all the magic to one side for a moment, there are some risks involved with hollow trees. Of course, where there are risks, there are also benefits and I wanted to run through some of these. If you have a hollow tree that you aren’t sure what to do with, this article might help you to make a decision. 

Why Do Trees Go Hollow?

Trees can live for an incredibly long time and throughout their lives, they go through various processes. Just because a tree has become hollow, that doesn’t necessarily mean that it is no longer healthy. 

The wood in the centre of the tree gets decayed by fungi and this is known as deadwood. It’s totally natural and something that all trees will experience as they age. Moreover, there’s hardly any chance of the fungi affecting the healthy sapwood as it’s just not interested in this. 

There in the middle of the trunk you’ll find lots of minerals which the tree has been storing for many years. Over time, as the fungi decays the wood, these minerals are released as a source of nutrition for the tree to continue its life. If it wasn’t for the hollowing trunk then the entire tree would have a real problem surviving. It’s thanks to these nutrients that the tree is able to grow new leaves and repair old branches. 

There Are Lots Of Well Known Hollow Trees

Earlier, I talked about the fairytale magic of a hollow tree, there’s just something captivating about it. And it isn’t only me that thinks this as there are many hollow trees that have been put to good use in a variety of weird and wonderful ways. 

For example, the Borrowdale Yews in Cumbria were the inspiration for one of Wordworth’s poems, Yew Trees, which was penned way back in 1803. Within this group of trees, you’ll find one whose girth is more than seven metres and you’ll comfortably get four people in the hollow at once. 

The biggest tree recorded in England is called the Marten Oak which stands in Cheshire. Amazingly, this tree has had more functions than some buildings having served as a pigsty, a pen for bulls and even a wendy house.

Moving down to Surrey and you’ll find the Crowhurst Yew which sits in a churchyard. You enter the hollow via a door and inside, there used to be tables and chairs although these were removed in the mid 1800s. 

Finally, we have the Pulpit Yew which stands in North Wales. Here, you will find an outdoor lectern which is said to have been used by John Wesley himself. Inside the hollow of the tree, there is a set of steps that take you up to a raised podium. 

What Are The Risks Of A Hollow Tree?

One of main concerns with hollow trees is whether they will fall or not. It goes without saying that, once the centre wears away so much, the tree will lose stability. But this doesn’t happen overnight and so mathematicians Mattheck and Breloer came up with the t/R ratio to determine how stable hollow trees are. 

The concept behind this ratio is the thickness of the good wood and the radius of the original trunk. The higher this ratio, the more chance the tree has of remaining upright. For example, it is thought that trees with a t/R ratio higher than 0.35 have very little chance of failing. However, if the t/R ratio is less than 0.1, there’s a very significant chance the tree won’t survive much longer. 

What Are The Benefits Of A Hollow Tree?

While there is a risk of a hollow tree failing, they are, for the most part, a beneficial part of our ecosystem. Largely this is because of how hollow trees provide shelter for wildlife. When animals are trying to shelter from the elements, the temperature inside a hollow tree is almost certainly guaranteed to be more consistent. 

Things like bats and birds love hollow trees for nesting as they offer a good degree of safety. Moreover, animals that hibernate can enter a hollow tree and be largely undisturbed over the winter. 

Another reason that hollow trees are beneficial is that they don’t pose as much of a risk in extreme weather. When things get windy, the structure of the tree means that it is more likely to bend as opposed to breaking. 

Should You Fell A Hollow Tree?

Trees are a vitally important part of the ecosystem, producing oxygen, providing fruits and food for humans and animals and acting as a form of shelter. Where possible, I would always recommend against felling a healthy tree. The only time I would suggest it is if it was posing a risk to a building, for example. 

However, if a hollow tree has a low t/R ratio then it might be time to cut it down before it starts to die off and possibly falls by itself. 

In the UK, there is an Ancient Tree Inventory and at the time of writing, there are more than 180,000 trees on this record. The Woodland Trust allows anyone to record an ancient tree in the hope that we will be able to offer better protection to these glorious giants. If you have one in your garden or you know of one in your local area, it’s worth doing your bit and adding it to the inventory. 


There are hollow trees all over the country. Some have gaping hollows that can fit several people while others are more suited to housing a family of small mammals. In any case, these trees are wondrous and magical. Moreover, they require protection. 

However, while most hollow trees are incredibly beneficial, there are some that are nearing the end of their lives and in this case, you may need to get rid of them.

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