Lightning Beware

We have been taught since we were children that lightning strikes the tallest​ object. It is no wonder then, that lightning​ is one of the most common natural​ causes of tree damage. ​

Lightning is formed when negative charged ions collect in a cloud.  At the same time positive charged ions are forming on the ground under the cloud and following it.  As the positive charges build under the cloud, they follow the contour of the ground.  If they travel up a tree, or another tall object, it may put them close enough for the electric charges make contact.  When that occurs, lightning is formed.

Lightning can injure a tree in many ways. Most ​of the time the damage is obvious. The heat from​ the lightning vaporizes the water in the tree turning it into​ steam instantaneously. The resulting pressure from the rapidly expanding hot steam blows the wood of the tree apart. Most of the​ time this happens toward the outside of the tree​ and we see it as a streak down the bark. Sometimes​ the damage is not so obvious. We may not see the damage because it has affected​ the root system or the interior of the tree. ​

What to do when your tree is struck

Lightning strike treatment in trees comes in two phases. ​ First, take care of any hazardous situations such as​ broken or hanging branches. Then comes the hard part. The true extent of damage to the tree is not immediately evident right after the strike because lightning comes in an infinite range of voltages and temperatures, . We should wait a few months to do any major corrective work. ​ By that time most of the serious damage will​ be apparent and a decision can be made as to​ whether the tree can/should be salvaged. In the​ meantime, timely irrigation and light fertilization is​ helpful in helping the tree compartmentalize the​ damage.

Massive lightning strike that caused heavy damage to this live oak.

It may be advisable to install lightning protection in a tree in certain situations such as, when a tree is a historic landmark, a specimen, or other places where people congregate such as a golf course.  Lightning protection systems use large copper cables that are installed high in the tree, down the trunk and into a trench in the ground away from the tree where the cable is connected to a ground rod.  This protects the tree and the people around it by giving the electrical charge a better conduit to the ground than through the tree.  Lightning protection systems can be installed by ISA Certified Arborists and must meet the standards of the Lightning Protection and Grounding Institute or the National Fire Protection Association.

If you are caught in a lightning storm

Finally, if you are caught in a lightning storm and cannot get to a building for shelter, follow the following safety rule recommended by the National Weather Service:

  • Avoid open areas. Don’t be the tallest object in the area.
  • Stay away from isolated tall trees, towers or utility poles. Lightning tends to strike the taller objects in an area.
  • Stay away from metal conductors such as wires or fences. Metal does not attract lightning, but lightning can travel long distances through it.
  • If you are with a group of people, spread out. While this increases the chance that someone might get struck, it prevents multiple casualties, and increases the chances that someone could help if a person is struck.