Why tree bark is rough

Bark is a tree’s skin.

It is tough and hard and protects the soft, inside part of the tree.

A tree trunk grows from the inside out. Each year, a ring of new, soft
wood grows around the trunk, inside the bark. This makes the trunk get
thicker. The old, hard bark can’t stretch as the tree gets thicker—it
cracks and splits and crumbles away to powder to make room for the new
wood. That’s why a tree’s bark always looks rough and cracked and bumpy.

As each ring of new wood grows, the outside of the ring becomes young
bark. A tree is always making new bark and shedding its old bark.

Some trees, such as the beech, have smooth bark. These trees grow
slowly. Their bark grows as they grow, and so the bark doesn’t crack and
split.

young and old bark

Tree bark grows from the inside. As new bark forms, old bark on the
outside cracks and falls off.