Most people I talk to have a fear of the awesome force we call lightning. When I visit homes with storm damage, lightning is blamed by the homeowner when in fact wind damages most trees during thunderstorms.

It is estimated that lighting strikes the Earth 9 million times a day -100 times per second. It is no wonder that trees can be damaged by lightning, but what is lightning anyway?

The electric charges that generate lightning are formed in large, very, very tall storm clouds. Negative charged particles collect at the base of the cloud. Since the Earth herself is positively charged the two forces fight to find a way to connect and cancel out by following the path of least resistance. Many times the tall tree out in the yard is that path of least resistance. An acting terminal if you will.

The voltage carried by a lightning strike averages 100 million volts and 500 amps. This is an awesome amount of energy! Trees are damaged because the living tissues of the tree serve as pathways for the surging energy. Moisture is instantly converted to steam which is why the bark of a struck tree appears to have been blown off.

Most serious is damage done to the root system as the charge grounds out.

Trees can be protected from lightning damage by installing lightning protection systems in them. Lightning protection systems do not attract lightning! I like to think of it as the ground (positive charges) is brought up to the top of the tree! The negative charges released from the storm are allowed to cancel out with the positive ones well above the tree leaving the tree out of it all.

Lighting systems are all copper – with air terminals connected to woven copper wire. The system is connected to grounding rods driven deep into the Earth to create a good ground. Trees which should be considered for lightning protection are those within 25 feet of a building, historic, rare and specimen trees.

Trees struck by lightning do not always die. They should be evaluated and monitored over time. Fertilization and watering are important. Insect pests such as ambrosia beetles must not be allowed to colonize these trees. Many trees will recover but could develop structural defects when exposed areas begin to decay. I have seen many a warrior Oak still standing tall and proud with old lighting stripes running down to the ground. ■

Larry Loiseau / Certified Arborist