According to the United States Precision Lightning Network (USPLN), Florida receives 33 lightning strikes per square mile each year. In the last two weeks we have gotten dozens of calls about lightning-struck trees at the Duval Extension Office. The recent storms seem more severe.
Just because your tree is struck by lightning does not mean it needs to be removed. However, patience will be needed.
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 to 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. The other thing to think about is that lightning is never the same. A tree can receive a minor strike, a major one, or hundreds of variations in between.
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.
It may be advisable to install lightning protection in a tree in certain situations — when a tree is a historic landmark, a specimen or in 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 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. If no shelter is available, crouch low, with as little of your body touching the ground as possible. Lightning causes electric currents along the top of the ground that can be deadly more than 100 feet away.
• 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.
Larry Figart is urban forestry extension agent from the University of Florida/IFAS.