Trees grow differently than animals and humans. We get larger in all of our parts, but we don’t add new parts (two legs, two feet, two arms, two hands...). Trees add new parts on older parts, small parts on large parts (twigs on branches), and the new parts also get larger over time (twigs become branches). A little branch that is five feet above the ground today will be a large branch five feet above the ground in twenty years. There is no set number of parts a tree can have; that number is determined by the combination of genetics and environment. Trees can overcome the loss of some of the parts of a given type (leaves, branches, roots), as long as not too much was lost. New parts will grow to replace the lost parts. Tree roots, trunks, and branches will slowly get thicker around over the years. This is because new layers of growth are added to the outside of the accumulated mass of previous growth. If the tree, or that part of the tree, can’t continue to expand its girth it can become stressed and even die. This happens because the little tube-like cells that allow water to move up from the roots into the leaves become crushed and the water movement stops.