About 10 percent of the wood mass of a tree is found underground in the form of roots. The root system of a large tree is enormous. The total length of all roots of a big spreading oak tree amounts to many hundreds of miles. The function of the root is to provide water and minerals for the tree and to anchor it securely to the ground. It is important to keep in mind that the roots are part of a living organism and that they need air, food, and water for growing. Mistreatment of roots, such as tramping the soil above them, flooding them for long periods of time, or burying them too deeply, will affect the welfare of the whole tree.