A crack is deep split through the bark, extending into the wood of the tree. They can occur in stems and branches and they may even extend up from the roots into the lower stem. Cracks are considered to be the most hazardous defect as they indicate the structural weakness of a tree. For example, when a tree has two cracks in the same segment of the stem, the stem can be separated into two sections of wood which move independently from each other. Figure 1 Figure 2 One of the most common reasons for cracks and splits on tree trunks is frost cracking.
Frost cracks originate at a point where the trunk was physically injured in the past.
Trees growing on poorly drained soils are particularly prone to frost cracks. Frost cracks often close during summer, only to re-open in succeeding winters. If cracks are only in the bark, they will not seriously damage it, although they do provide openings where certain disease organisms may enter the tree, particularly if the tree is in a weakened condition. Maples and sycamores are very prone to frost cracks while apples, ornamental crabapples, ash, beech, horse chestnut and tulip tree are susceptible. Isolated trees are more subject to frost cracks than trees in groups or in forest settings.