How do trees heal?

I am not a tree expert, but here are some basics. I am not sure how sap stops “bleeding” when a tree is cut, but indeed trees can withstand cuts and even whole limbs being cut. When a tree loses too much sap it can lose it’s health and even die. Maple trees that are tapped for their sap to make maple syrup has to be done with care and not excessively. The owners watch the tree, and if it starts to show signs of becoming weak they will stop draining the tree of sap, maybe skip a year or two completely for that particular tree, so it can build back its health.

Trimming trees back can help a tree gain new healthier growth. Limbs that are not doing well are a drain on the tree, as the tree still supplies nourishment to it. Cutting means the tree can give its resources to younger healthier growths. But, if a tree is cut back too much it cam go into shock and die.

Trees respond to wounding or injury in two ways: compartmentalization and the development of barrier zones (Shigo 1986).

Compartmentalization

When a tree is wounded, the injured tissue is not repaired and does not heal. Trees do not heal; they seal. If you look at an old wound, you will notice that it does not “heal” from the inside out, but eventually the tree covers the opening by forming specialized “callus” tissue around the edges of the wound. After wounding, new wood growing around the wound forms a protective boundary preventing the infection or decay from spreading into the new tissue. Thus, the tree responds to the injury by “compartmentalizing” or isolating the older, injured tissue with the gradual growth of new, healthy tissue.

Barrier Zones

Not only do trees try to close the damaged tissue from the outside, they also make the existing wood surrounding the wound unsuitable for spread of decay organisms. Although these processes are not well understood, the tree tries to avoid further injury by setting chemical and physical boundaries around the infected cells, reacting to the pathogen and confining the damage.

Source

Research on how trees heal wounds

As long as the inner bark of the trunk (cambrium ?) isn’t cut around the entire base of the trunk the tree is pretty resilent to any cuts.

In any area around houses and building, take a look around and you will see lots and lots of spots on trees where limbs were removed, especially next to sidewalks and roads.

People trim off all the branches low enough to interfere with traffic. It’s a constant chore, like trimming your fingernails.

Same way as animals do. Gene expressions to replace the damaged parts.