How does epidermis get replaced by bark?

The epidermis of a tree is replaced by bark as the tree grows. As the cambium layer produces new cells, the outer layers of the tree expand and push the existing epidermis outward. This outer layer eventually becomes the protective bark, which consists of dead cells that provide insulation and protection from environmental factors. As the tree continues to grow, the bark will periodically shed and regenerate to accommodate the increasing girth of the trunk.