Why Do Some Trees Have Hollow Trunks?

in parks, or in the fields you may find some old trees that are hollow in their trunks. With their bark not broken completely, they are still alive. However, the wood cannot be used for building materials any more. The hollow is caused by a dis- ease. When a trunk is broken, bac-teria get into it and multiply there. They eat the wood to get nutrients for living. As time goes on, the wood becomes hollow or even rot- tell. Therefore, when workers find gaps or cuts on trunk bark they will seal them.