Will hammering a nail into a tree kill or harm the tree?

Hammering anything into a tree is intrusive and will cause harm; a tree is a living organism and an injury such as this is damaging.

The outer bark layer on a tree stem protects against disease and decay, anything that breaches it can allow the entry of harmful organisms.

The significance of any harm will depend on a number of factors such as the extent of the injury, the species and age of the tree and its overall condition.

For example, a single nail is unlikely to cause great harm to an established tree that has natural durability such as oak or sweet chestnut but it could be more harmful to a tree with lower durability such as birch or poplar.