Bark is like the “skin” of the tree. Just like how our skin protects our inner parts, the bark of a tree protects the layer known as the “phloem”. The phloem is the innermost living tissue of the tree, and it transports the sucrose made through photosynthesis to where it’s needed. Without bark, this sensitive tissue would be open to superficial damage, infections, and insects.
This means that when the bark is damaged, the “circulatory system” of the tree is open to damage as well. Trees have healing measures that can help them repair the tissue so that diseases do not harm the movement of nutrients throughout the tree. However, this healing does not help bark grow back, but humans can help tree wounds heal cleanly so that what replaces it is just as protective.