In transplanting (digging up a tree or shrub and replanting it somewhere else)?

Question

Which particular roots and parts of the roots are usually damaged?

Answer 1

tap roots snap off and the root hairs lose soil contact

Answer 2

Usually the lateral (secondary) roots and fine roots will be damaged.  The main tap root should remain intact.

Answer 3

The root hairs which are very small and fragile are damaged when transplanting.  This is problematic for the tree or shrub, because the root hairs are the area of the root where water and nutrients are absorbed.  That is why you want to collect a lot of soil around the plant to protect the root hairs.  When plants have "transplant shock" it can be the time when they are replacing the root hairs, which can negatively impact the plant.