When a lumber company travels to a site to cut down trees it's likely that they won't simply go around taking the exteriors of the trees since it is the entire tree that is used in various woodworking pursuits. For example, the sapwood portion of the tree which is close to the exterior isn't usually employed as a woodworking material but the inner portion which is called the heartwood is the portion of the tree with which wood workers will prefer to work. The heartwood is a sturdier part of a tree and for this reason it is highly valued.