The diameter of the hollow in this yellow birch, Betula alleghaniensis, is the diameter of what was the main stem that died 60 years before the tree was cut. In 60 years the decay did not spread into the wood that formed after the main stem died. A branch then became the new leader stem. The greatest diameter of a hollow or of a decayed column of wood will be the diameter of the tree at the time of wounding or of the death of roots, stems, or branches. The infected wood is walled off or compartmentalized. Mature trees may live in a healthy state while having thousands of compartmentalized infections. Compartmentalization in a generating system gives trees a much longer survival time after injuries and infections than animals that have healing in a regenerating system.