My tree has a large crack in the trunk. Is it dangerous?

Trunk cracks are one of the most significant structural defects in trees, and they range from cosmetic concerns to imminent failure hazards. The type, location, and depth of the crack determine the risk level.

Types of trunk cracks:

1. Frost cracks (radial shakes): Vertical cracks that open in winter and partially close in summer. Caused by rapid temperature changes. These are common on thin-barked trees (maples, cherries, lindens). While unsightly, they rarely cause structural failure on their own.

1. Included bark cracks: Cracks at the junction of codominant stems (two trunks of equal size). The bark gets trapped between them, creating a weak point. This is the most common cause of large tree failure during storms.

1. Shear cracks: Horizontal or diagonal cracks that indicate the trunk is splitting under mechanical stress. These are extremely dangerous and may indicate imminent failure.

1. Lightning scars: Spiral or vertical strips of missing bark from lightning strikes. The tree may survive but is structurally compromised.

1. Seams from old wounds: Callus tissue that has closed over an old injury. Usually cosmetic unless decay is extensive behind the seam.

When a crack is dangerous:

• The crack extends through the entire trunk (you can see daylight)
• Two or more cracks on the same trunk increase risk multiplicatively
• The crack is associated with a lean or signs of movement
• Decay or hollow is present behind the crack
• The crack is at a codominant stem junction with included bark

What to do:

1. Keep people and property out of the target zone (the area where the tree or parts could fall).
2. Have a certified arborist perform a risk assessment — they may recommend cabling, bracing, or removal depending on severity.
3. For codominant stems, steel cables installed high in the canopy can significantly reduce failure risk.

See our guides on Cracks in Tree Trunks, Signs a Tree Might Fall, and Is My Tree Dangerous?.