A tree under repair does not truly heal in the classic sense of the word. The damaged tissue does not undergo the same sort of process that, for example, a human wound does. Most of the exposed tissue simply dies, that is digresses to dried xylem for the most part. This portion may even become punky and infected with decay organisms. This does not normally spell trouble for the tree. The course of action is that of compartmentalizing. This is the formation of a distinct division between sound and dead material. We liken it to a damaged ship closing off bays to prevent sinking. Callus tissue and further growth eventually will surround the wound and encase it. A later observer coming to the site may surmise the wound had healed, but if the tree were to be cut open it would still reveal the damaged part hidden inside and clearly defined. Below is a photo from our woods which shows new growth beginning to envelop a scar in a maple tree (the wound is the gray wood in the center). If we return in a few years the wound will be invisible, hidden inside the new tissue layers of the ever expanding cambium.