Tree Wounds

Trees are long-lived organisms that fill a variety of roles for other creatures. As such, trees can be subject to a lot of punishment over the years and will often accumulate wounds. These wounds can range from small gashes to severe breakages during storms. Because trees don’t heal in the same way as humans, it can be difficult for arborists and gardeners to know how to deal with tree wounds. Many methods employed by humans may end up harming the tree even more. This article will cover what tree wounds are and how trees respond to them. We’ll also go through some of the methods used to help wounded trees and examine how effective they are.

What is a tree wound?

Trees can collect several wounds throughout their lifetimes. A wound typically refers to any damage that breaks through the tree’s protective bark layer and exposes the inner wood of the tree. These injuries are often entirely natural and can include:
  • Surface wounds from the claws and teeth of animals or birds
  • Burns from fire damage
  • Invasion of the tree by pests like bacteria, fungi, or insects
  • The activity of nest-building animals
  • Weather damage from storms or strong winds.
Human activity can also cause damage. Any form of tree maintenance such as pruning or trimming will inevitably wound a tree in some way. Wounds are simply a natural part of the life of a tree and can’t really be avoided. If the tree can’t overcome its wounds quickly, it becomes more susceptible to disease and decay. This can cause structural damage and cannot be reversed once it has taken hold. Long-term issues can only be managed or prevented.

Tree response to wounding

Trees do not heal in the sense that humans understand. Instead, trees have two main methods of dealing with wounds; compartmentalisation and barrier zones.


A wounded tree cannot regenerate the damaged tissue like an animal or a human would. Instead, the tree will seal off the wounded area to prevent the damage or disease from spreading to other parts of the tree. This impressive ability involves the production of protective callus tissue around the edges of the damaged section of the tree, creating clear separation between damaged wood and healthier bark. The wounded region is gradually covered by new wood growth as the tree recovers. The wound remains present forever underneath the surface of the bark.

Barrier zones

In addition to compartmentalising the wound, a tree will also deploy a series of barrier zones throughout the wood surrounding the damaged area. As far as we currently understand, this involves the release of specialised cells to create an extra layer of defence against the spread of the damage. This confines potential diseases and pests to a single zone, allowing the rest of the tree to continue growing without becoming infected. This technique must be deployed quickly before the infectious bacteria has a chance to spread further through the tree. Younger trees that are growing more actively have a better chance to deploy barrier zones effectively.

Caring for tree wounds

Although trees have their own protective measures that have been honed over millennia, arborists and gardeners can still take some steps to help a tree deal with wounds more efficiently. However, some of the techniques in circulation may actually cause more problems than they solve.

Physical repair

When part of a tree has received a wound, the bark is usually torn and ragged. To help the tree start its recovery process, gardeners can trim away any pieces of damaged bark. Use a sharp knife and try to avoid cutting through any healthy bark. The best thing to do is to attempt to shape the edges of the wound into a vertical eye shape running down the branch or trunk. This gives the tree a good starting point for deploying callus tissue around the damaged area.

Wound dressing

One of the commonly prescribed treatments for tree wounds in the horticultural industry is some form of wound dressing. These typically take the form of products like pruning paint or sealer. Products like this are designed to seal the wound to protect it against disease or water damage. However, there is verifiable evidence that these products actually hinder a tree rather than help it. Many wound dressings contain ingredients formed from petroleum and can damage the tree by inhibiting its natural defence mechanisms like compartmentalisation. These methods should be avoided.

Cavity filling

Cavity filling is another common tree wound treatment that has questionable effectiveness. It essentially involves filling any cavities or hollows in a tree trunk with other materials such as brick or concrete. The idea is that these additions help preserve the rigidity of the tree, but this doesn’t help that much. The only slight benefit to cavity filling is that it can help provide a stable starting point for the callus tissue. But in most situations, it won’t help. It is also an extremely expensive method that provides virtually no benefit to the tree. Cavity filling cannot halt the spread of disease or decay and the process of filling the tree may inhibit the formation of callus tissue, placing the tree in greater danger.

Pruning wounds

Improper tree pruning can cause avoidable and unnecessary damage to perfectly healthy trees. But by avoiding bad practices and deploying the correct pruning techniques, gardeners can put their trees in the best possible position to recover. Pruning is used to remove dead or diseased branches and to keep a tree to a manageable size. Any pruning cuts should be clean and smooth and made at an angle that allows the tree to grow new branches in the desired direction. Branches should be cut right back to just in front of the collar. This is the section where the branch meets the main trunk of the tree. The collar is identified by a slight bulge at the base of the branch. By pruning branches back to this location, the tree doesn’t have to expend as much energy sealing the wound. Cutting branches here also creates much smaller wounds than if the branch was pruned to be flush against the trunk. The time when pruning is carried out can also have a huge effect on the tree’s ability to recover. Trees should not be heavily pruned during the spring and summer growing season as this can stunt growth. Winter is the ideal time for pruning trees as most species will be dormant at this time of year. There are also less harmful pathogens present in the winter months that could infect any open wounds.


To summarise, trees will naturally suffer wounds regardless of what gardeners try to do. It’s an unavoidable fact of being a tree. Instead of regenerating damaged tissue, trees will simply isolate the damaged areas and redirect their energy to healthier sections. Some horticultural practices that can make tree wounds worse, such as pruning paint or cavity filling. The best way to help your trees deal with wounds is to use the correct pruning form at the right time of year. This reduces the strain on the tree and keeps it growing healthily and happily.

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