Trunk Damage

Trunk damage can be the most hazardous type of damage because it often results in the tree being incapable of remaining standing. While a tree may be able to withstand damage to a portion of the branches or roots, the tree only has one trunk and severe damage to it will often necessitate its removal.

Common damage:

Broken trunks
Twisted trunks
Cracked trunks
Bent trunks
Stripped bark
Wood fiber detachment

Colossal trunk failure caused by a tornado, Oklahoma 1999

Courtesy of The Tree Bank Foundation

Broken trunks usually are caused by high winds or heavy weight on the crown (the branches) of a tree. Trunks tend to break where trees fork, where the trunk has internal rot or a prior crack, or when the roots allowed excessive trunk movement. Broken trunks can not be repaired or remediated; the only option for a tree with a broken trunk is to remove it.

Broken trunk, Oklahoma 1999

Courtesy of The Tree Bank Foundation

Twisted trunks will have the same hallmarks that twisted branches have:

odd angles

spiral appearance to the bark

exposed wood where the bark has twisted

Twisted trunks are most common with young or small diameter trees that are flexible enough to twist without snapping the trunk. Trunks of larger, older trees will tend to crack or break when twisted, so they often do not appear twisted. A young tree may recover from having a twisted trunk, but the tree should be monitored every six months to check for trunk cracks, breaks or misshapen/abnormal growth.

Twisted trunk that contributed to the tree's failure Oklahoma 1999

Courtesy of The Tree Bank Foundation

Cracked trunks usually occur where a tree forks or where several branches come from the same location. The thing to remember about damaged trees is that they are different from hurt people. People can heal, but trees can only partition off the damage, seal it off. The key to a cracked trunk is that once it is cracked, it will always be cracked.

Search for cracked trunks on:

Trees that fork

Older trees that have heavy crowns with large branches

Trees that commonly crack, such as Bradford pear, silver maple, elms, cottonwood, pecan, etc.

Typical cracked trunk caused by wind, tornado, hurricane or ice damage Oklahoma 1999

Courtesy of The Tree Bank Foundation

A special kind of cracking results from lightning. If lightning only shears the edge of the tree, a vertical scar and crack will form on the trunk. As the tree grows tissue to cover the crack, it will gain a raised appearance similar to a snake crawling up the tree just under the bark. Trees will often seal off cracks caused by lightning and remain structurally sound.

Bent trunks are common from ice storms and occasionally from wind storms.

How a trunk becomes bent:

The branches, trunk and leaves of a young tree are coated with ice or bent under heavy winds.

The weight exceeds the trunk's ability to stay upright.

The weight is redistributed by the trunk bending over.

Although no damage is good damage, a bent trunk is one of the few preferable types of damage during an ice storm. It indicates that the tree was healthy enough for the trunk to bend and not break. Many trees will stand back up once the ice has been removed. For trees that do not correct the bend themselves, stake the tree so that it is upright and then monitor it.

Stripped bark results from something impacting the tree and tearing the bark off or from internal explosion, as with lightning. The risk of the tree dying will be proportional to the amount of bark removed. If only a small amount of bark has been removed in a few places, the tree should survive. One special case of stripped bark is girdling or the removal of bark all the way around the trunk in a continuous circle. Girdling stops the movement of water and nutrients through the tree and will eventually cause the tree to die.

Wood fiber detachment is a fairly unique condition caused by lightning. When a tree is struck by lightning, the sap and moisture in the tree heat to extreme temperatures, turning from liquid to steam. The steam then forcibly escapes through existing cracks in the trunk and, in many cases, by creating new cracks. Imagine an accordion effect where the tree expands laterally on all sides and then when the pressure is released, the wood and bark crash back in on themselves. Massive trunk failure usually occurs because the strength of the tree is destroyed by the wood fibers detaching from each other.

The force of escaping sap, superheated by a lightning strike, blew this tree's wood fibers apart. There is an accordion effect in which the fibers are forced away from each other and then come crashing back in. Oklahoma 2003

© Veronica Keithley, Cross Timbers Forestry

Common trunk damage

Tornado Broken trunk Cracked trunk Twisted trunk Stripped bark		Ice Storm Broken trunk Cracked trunk Bent trunk
High winds Broken trunk Cracked trunk Twisted trunk		Lightning Broken trunk Cracked trunk Stripped trunk Wood fiber detachment
Hurricane Broken trunk Cracked trunk Twisted trunk Stripped bark		The storm names link to general information about each storm.

How a damaged trunk weakens a tree:

Support to keep the tree standing is weakened

Reduced ability to move water and food through the tree

Break in bark's protective layer

Determining the extent of damage
will take you through the process of evaluating the damage to your tree.

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