Numerous layers of living and non- living tissue protect trunk, roots and branches from mechanical injury, and the effects of sun and wind. As we know, injuries which tear through bark are common. Animals, accidents and human activity constantly breach this first line of defense. The new wood is highly resistant to decay, and will remain sound unless another wound or infection occurs. Decay is a factor of the success of the chemical walls which compartmentalize infections.
Wound closure is good, in as much as liquid transport within a tree works best in a straight line.
But wound closure will not protect against decay from the wound inwards if the tree is too weak to chemically protect itself. The success of this process depends mainly on the overall vitality of the tree, and also on the size of the wound. A weak tree, such as a new transplant or a street tree, may not be able to form chemical walls to protect a moderate size wound. And even an olympic tree can be overwhelmed by a huge wound. Sometimes, the barrier system is breached by the infection.