Below is a message from the Tree Advisory Board with information about how a lightning strike may affect a tree. This edition of Tree Talk with the Tree Advisory Board is written by Tree Advisory Board member, Jinny McCormick, and edited by Jonathan Perkins, arborist and Tree Advisory Board chair.
How Lightning Strikes Affect Trees
Summer weather isn’t always sunny. July is a top month for thunderstorms, and Western Kentucky averages 15-20 thunderstorms per year. With thunder, of course, comes lightning. Lightning strikes on trees can certainly kill them, but not always.
Trees are a precious commodity, so you will want to protect yours, and if one is hit, save it if you can.
What May Happen When a Tree is Hit by Lightning
Wood doesn’t conduct electricity very well. Lightning actually travels through the moisture inside the tree. Plants have a vascular system that moves water and nutrients through tube-like structures called phloem and xylem. It is through these that electricity will travel. Lightning is hotter than the sun, so that moisture or sap might boil, and the intense pressure can cause the wood fibers to explode. If lightning travels through the phloem near the bark, the tree will be scarred or may suffer a crack. If it is in the xylem further in, it will split or begin to split the trunk.
Unfortunately, a tree with a split trunk or other deeper damage must be removed because it no longer has structural integrity and is a hazard.
If the tree is not visibly split, deeply cracked, or hasn’t lost significant bark, keep a close eye on it for the next several weeks. The tree may have interior damage that shows signs of distress slowly. Trees near structures or other high-value areas should also be removed if they have deep cracks in the trunk or if more than one-third of the bark has fallen off. Be aware that what may look like a surface crack can widen or deepen over time. Continue to evaluate the tree over time for signs that the damage is deepening.
Significant damage that is not on the inside includes more than ⅓ of the bark being lost, a spiral of bark around the whole circumference, or a deep inner crack.
The lightning strike isn’t the only danger. The removal of the bark has opened access to food for insects. Your priority after the strike is to prevent further damage by pests and decay. Consider a professional assessment of the damage to determine if anything needs to be removed to prevent decay or damage to surrounding assets if limbs or the tree might fall in the future.
There are preventative pesticides in both spray-on and injectable applications. Injectables can only be applied by an arborist. Some spray-ons have to be applied to the entire trunk of the tree and then applied again in a few weeks. If the scar is small, you may be able to spray only around the scar. Bark tracing, which is skillfully cutting around small scars, may help prevent further decay.
Can You Prevent a Lightning Strike?
It’s possible. High-value, historical, and ornamental trees in landscapes like golf courses are often protected by tree lightning protection systems. These systems also protect homes and buildings from side flashes - lightning that travels from a tree to a structure. These systems aren’t foolproof, so the building should have its own lightning protection system as well. They do not always protect humans either, due to step voltage. Step voltage occurs when lightning is dissipated through the surrounding ground. To learn more, see the International Society of Arboriculture’s information on tree lightning protection systems and how they work.
Resources
Adapted and summarized from Alabama and Auburn University’s Extension, Bartlett Tree Experts, ISA, and Forest Keepers.
