Forked trunks are signals of potential weakness, especially if one side of the fork has grown outward instead of upward like the other. Narrow-angled forks are also prone to infection, often indicated by sap or pitch being exuded. Look for Tree Balance Leaning or lopsided trees present more of a hazard than those growing vertically, but if a tree has always grown off center, it generally is not an undue risk. However, any sudden lean indicates breakage or weakening of support roots and should be cause for alarm and immediate action. Sometimes there are no outward indications.
Arborists then use one of the methods shown below to check for decay.
Examine Wounds and Cracks Any trunk wound is an opening for decay. Wounds extending into the ground, including lightning scars, should be of particular concern and examined regularly. Some cracks, such as frost cracks, have little effect on the strength of a trunk. However if two vertical cracks appear on opposite sides of the tree, it can be a sign of root injury or breakage. It is usually associated with a circumferential separation of wood internally and is extremely dangerous.