Cracks A crack is deep split through the bark, extending into the wood of the tree. Cracks are physical separations of the wood (Figure 1 and 2). 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. One section slides over the other creating tension and the crack elongates (Hayes, 1997, Robbins, 1986). 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. In some cases when a scar or cavity forms, the wound will not heal properly at the edges. The wound tissue may roll inward as it grows, failing to close. This process will continue and outward pressure will be exerted on the stem, causing a crack to form. Figure 3 The evaluation of cracks is based on the number of cracks (splits), where they occur and if they are in contact with another defects such as, rot or a cavity. Three classes of cracks are defined using the following rating:     0 Tree does not have major cracks either on trunk or major branches. 1 One minor crack extends into the stem, major stubs or a branch of significant size. A minor crack is one that enters the wood (not just in the bark) but does not extend more than ‡ of the distance to the centre of the stem. No "Ram’s Horn" (Figure 3) 2 Two or more minor cracks occur in the same general area of the stem, but there are no other defects in contact with the cracks; The crack condition is more serious than class 1, but less than class 3. 3 A crack(s) is in contact with another defect (e.g. rot, poor branch attachment, lean); Tree has one deep crack where one-half or more of the tree diameter is structurally compromised; A crack has "Ram’s Horn" (Figure 3) appearance; Crack(s) in the tangential (horizontal) plane. Tree ProblemsRoots