Tall wooden sculptures can pose a great hazard, particularly later on in their life, especially in public places.

Over the years I have worked as wood sculptor I have occasionally been asked to carve tall tree stumps. I have actually carved very few personally, but do hear of other carvers regularly working on stumps that require 2lifts of scaffolding, and higher. I believe a number of these tall sculptures amount to a ticking time bomb on the sites that they are situated. The reasons for coming to this conclusion are based on my personal experience with working on dead, dying, diseased, and damaged tree stumps on a wide range of different sites. Also, my contact with other carvers when chatting at shows and events about their experience, plus some personal encounters with previously carved stumps.

Why should these lovely big carvings be dangerous?

First of all, timber rots.
Some trees earmarked for carving have died or been damaged. When a tree is dying, or dies, there are often signs that advanced rot from fungal attack has been part of the reason for its demise. If a tree sheds a branch (which then has it flagged as dangerous), this is also often down to some form of fungal degradation or rot.
It is always unfortunate when trees become badly damaged or die as often they are much loved features in a landscape or neighbourhood. So occasionally it will be decided to have something notable done with the remains to offset the loss. Now and then, the good idea that surfaces, is to have the remains carved. The fact that rot exists can often be overlooked, especially when the timber in the stump seems hard and sound.

It is at this point the time bomb can be primed if it is decided to make a spectacular carved feature of the standing stump. The time bomb won’t be anything like the same problem if the tree is felled and the trunk is carved into low level sculptures on the ground.
Either way, the remains will rot. Quite quickly with some species of timber, slower with other species. The main problem with the standing stump is that it can’t be easily inspected for signs of structural degradation above head height. A short ladder can extend that to about twice head height, short ladders being easy to transport, and not requiring any official to risk being over the dreaded 2m off the ground (after which he/she might need a harness or special training, which then makes the inspection very expensive).

The standing stump will rot in various places at various rates, not all of them will be easily observed. Some species will develop serious structural problems within two years.
To begin with, the only indication might be a hollow sound when the trunk is tapped, this being possibly the most dangerous outcome as it really is down to guesswork just how structurally weak the timber actually is. It may be left in-situ as “probably ok” then fall on someone who leans against it a few weeks down the line. The higher the carved stump is, the more dangerous. Pieces can fall off unexpectedly from height, potentially hitting anyone standing below.

The various points to particularly watch out for rot are:

Near ground level where the stump wicks up water from the ground and has the ideal moisture content to encourage rampant rotting. Usually can be seen but may be hidden if the trunk has had a coating of preservative. This can create a skin of preserved timber hiding a rotten core.

Holes left in the trunk from shed branch stumps that rotted out when the tree was alive.

In the crooks of branch forks, especially with the likes of beech which commonly has bark inclusions at these points. These would have been fine when surrounded by live wood, but rot very quickly when the tree is dead.

Splits and cracks and where end grain is exposed (the cuts resulting from the branch and higher trunk removal).

Anywhere water can collect or pool.

The whole trunk/sculpture can be hollow especially if it had a coating of preservative applied after carving. This can result in a relatively sound skin of timber overall, with a core of dry, soft, rotten spongy wood. Often the point at which woodpeckers excavate nests.

Anywhere that has had other sections of timber added, spliced in or mortised.

The sapwood of some species can be particularly good at soaking up water and rotting.

As has already been mentioned, some timber species rot faster than others, and can rot in a different way too.
Timbers that can be carved from standing stumps comprise only of the most rot resistant varieties.
For example, native Oak (only the heartwood), Sequoia (heartwood only), Robinia, Yew, for a small sample. None of these tend to develop invisible rot.
Nearly all of the other broadleaves will rot fairly quickly.

Trees that are destined for removal that are not dead, dying, and diseased or damaged, if not of the most naturally durable species should not be carved into sculptures higher than around 3m. This is the maximum height at which they can be easily inspected for degradation.
Once carved, the timber can soak up a lot of water as there is no bark to keep the rain out, this can be particularly bad with timbers that tend to be very porous when seasoned (e.g. Corsican pine), leads to accelerated rot.

The dangers posed by tall, carved tree stumps (apart from the very durable varieties) are worse in areas of public access. They should never be higher than 3m in public parks. The risk of being climbed on and of injury resulting from structural failure, should also be considered.
A similar consideration should be given, to the dangers posed, regarding suspending wooden items high in trees. These items will still rot and the fixings may give way.

If the tree/stump is on private property, without public access, then the risk is down to the owner’s discretion. However, the sculptor should make it very clear to the client the risks associated with carving a tall sculpture.

As an alternative, the tree can be felled and utilised for low level sculptures. If the sculptures are off the ground on rot resistant chocks, brick or stones, and don’t collect pools of water, they can last for a good many years.

Sculptors, consider who is likely to be liable for injuries resulting from a carvings structural failure.