How can a living tree be hollow and still be healthy?
The living part of a tree trunk is a thin layer of tissue called the cambium. It is just under the bark. The center of the tree trunk, which is called the heart wood, is made up of dead tissue. If the tree is injured, exposing some of the heart wood, it may start to decay. This reduces the strength of the tree trunk, but it also makes the trunk lighter, which helps balance the weakness. Hollow trees can be quite healthy, and can live very long lives, even with raccoons living inside them.