Beverly Thomas, age 12, of Rockingham, North Carolina, for her question:

Why do trees have bark?

The crusty bark around the trunk and boughs helps to protect the woody parts of a tree. The outer edge of the wood is very precious because it is made of the newest, most useful cells. Also, just under the bark is a layer of very special cells that build rings of new wood every year. This is the thin cambium layer, the only part of a tree trunk that can grow new wood. The bark helps to protect it from frost and drying air, also from scratches and other wounds.

Some trees have thin bark that peels away in strips. They may weaken the outer layer of wood and if the bark is stripped from all around the trunk, the tree dies. Insects almost always invade thick spongy bark and a few of them burrow down into the wood. But if the tree had no bark, those bugs would do even more harm to the growing layer of cambium.