Lightning and Trees

— Written By Peg Godwin and last updated by
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Trees are frequently valued for the beauty they bring to the landscape. Despite all our efforts numerous elements beyond our control can damage the materials we sought to protect. Each year in the United States more than a million trees are struck by lightning with the southeast having the highest frequency of storms with lightning.

Tree and lightning are not allies. Afternoon thunderstorms are common in eastern NC during the summer months and trees are regularly damaged by lightning. Many trees grow quite tall which puts them at considerable risk for attracting lightning. Other issues that put trees at risk from lightning are their location and their size. The greater the mass, the greater the chances of encountering a lightning strike. Trees that stand alone and trees in close proximity to water or sources of metal (such as water towers) also have increased chances of being struck.

Different species of trees vary in the chances of being struck. Oak are the most likely to be struck followed by pine, gum, poplar, maple, and birch.

The evidence of lightning damage in trees varies considerably. Sometimes, a tree splinters or shatters when hit. In other trees, lightning blows off a strip of bark. Still others appear undamaged, yet suffer unseen root injury. Depending on the severity of the strike, considerable damage may be done to the tree internally, the effects of which may not be immediately apparent. It may take months to know the true extent of the damage, and the understanding of the tree damage may come after much investment of time, energy, and resources.

Examples of lightning damage include: the tree dies within a few days, weeks or months, most of the leaves are lost but it re-foliates, cracks form down the side of the tree, the top of the tree declines over several years, cankers and dead spots form along the trunk, root rot fungus attacks, sprouts form along major branches or the trunk.

The fate of a tree depends on the course the lightning took. If rain is pouring down the bark, especially on smooth-barked trees, the electricity may flow down the outside of the tree and do no harm. In dry conditions, the current may travel through the wood and cause a crack or explosive rupturing of the wood. Old trees with increased decay are more likely to explode or be severely damaged.

During the spring when the cambium contains high salts and sugars, the path for electricity is in the developing phloem and xylem. This may result in a strip of cambium being killed and the bark popping off. Sometimes the current boils the entire cambial layer and kills the tree.

Observation is the key to help your tree. Broken branches should be removed for safety. If you are aware a tree on your property has been struck by lightning there are several things you can do to reduce the stress on the tree. Be deliberate in providing water for the tree especially during dry times. Open wounds and cracked bark provide easy entrance for pests from insects to bacteria and fungi. Pruning out torn wood may help the tree close wounds more quickly but extensive pruning is not recommended. Fertilization may be beneficial to help the tree replace lost foliage.

Lightning can have many different effects on a tree depending on what kind of tree it is, how much moisture it contains, the overall health of the tree, the time of the strike and the intensity of the lightning.