Basal/Trunk Scar(s) Figure 2 Figure 3 A scar is formed when the bark of a tree is damaged to such an extent that the wood underneath is exposed (Figure 1). As such, they can form the point where decay begins. Scars may be old and show some signs of healing over or they may be relatively new. Damaged bark alone does not necessarily constitute a risk to the tree. Damage to the bark that exposed the wood at some time should be considered a scar. Figure 1     The most frequent cause of scars on urban trees is vandalism. Other causes include: the girdling of trunks by lawnmower damage; the bark of trees growing near driveways and parking lots have been repeatedly injured by vehicles, bicycles, etc;      lightening; frost cracks; or sunscald. The size of the scar relative to the size of the tree is important. For example, a 5 cm scar on a tree with a diameter of 10 cm is more serious than a 5 cm scar on a tree of 50 cm "diameter breast height" (dbh). As a rule-of-thumb, scars that have widths greater than 1/8 of the circumference of the stem on small trees (less than 30 cm dbh) and any scars greater than 10 cm wide on larger trees (more than 30 cm dbh) should be recorded. Stems may also become cracked due to frost. These cracks may heal over and the scar tissue will form a long ridge along the stem. These cracks are classified the same way as scars. In this category, we are most interested in damage appearing near the base of the tree, below the crown. Similar damage higher up on the tree is assessed under other categories. Tree ProblemsConks