Lightning strikes millions of trees each year. Though not many trees die immediately, strikes often cause serious structural weakness. This damage increases the risk of branches falling and predisposes the tree to insect and disease infestations. These trees are often a safety hazard and pose risks to nearby property. A lightning protection system can help minimize the potential of a lightning strike to a tree. Lightning protection systems use copper conductors connected to a ground rod to conduct the electrical charge to the earth where the energy is dispersed. They have an excellent record of protecting trees.
What is a Lightning Protection System
Lightning protection systems do not dissipate an electrical charge. Rather, they offer a way to more safely conduct the strike to ground. We will install a terminal near the top of the tree and a copper conductor that runs down the trunk to a grounding system. Regular maintenance ensures the system remains in good working order. Maintenance consists of annual visual inspections from the ground and a closer, in-tree inspection about every five years or whenever the tree is pruned. The main elements of the system that need maintenance are: (1) drive fasteners which can be overgrown by the tree, (2) the air terminal which stays at a fixed height while the tree grows upward and (3) conductors which can deteriorate or be severed.
Some people wonder if having a system increases the chance of a lightning striking the tree. Systems do attract lightning, but in a relatively small area. A strike coming down within a 50- to 100-foot radius of a protected tree is likely to be diverted to the tree’s system. This is a positive. The system will help direct the charge into the ground and reduce the potential for damage to the tree.
Why Install Tree Lightning Protection
In addition to protecting trees from damage and even death, a lightning protection system can also be a safety precaution. Struck trees often incur torn bark, damaged branches, and other structural issues. These issues significantly increase the risk of falling branches, which can be hazardous, particularly on properties where people walk and congregate.
What Trees Are Susceptible
Susceptibility to lightning strikes varies by tree species. This is because of differing bark and internal electrical resistance characteristics. Two of the most susceptible are tulip poplar and black locust. Therefore, they are higher priorities for protection. Ash, catalpa, elm, hemlock, maple, oak, pine, and spruce are other species that display a susceptibility to strikes. However, species is not the only factor to consider. The location is also critical.
Large and highly visible trees are often more prone to strikes. On a property, look for tall and open-grown trees, trees on hilltops or those close to water, and the tallest tree in a group. Trees that are growing close to buildings may also benefit from a system. These trees can attract lightning which can then ‘side flash.’ This means that the lightning jumps from a tall tree to a more conductive building or structure nearby. Just keep in mind that if you are concerned about lightning strikes to a building, you should install a system specifically on that structure. You cannot count on a tree lightning protection system to protect an adjacent building.
When thinking about your trees, protection is also important for high value, memorial or historic trees. Also consider any trees where people like to congregate. A knowledgeable arborist can provide guidance and information on proper installation of lightning protection systems.
What if Lightning Strikes an Unprotected Tree
Lightning affects every tree differently. Some are immediately shattered while others have no apparent damage. Regardless of what the external damage looks like, it is possible that the tree has suffered internally. In some cases, trees suffer extreme root damage. Trees with lightning-damaged roots rarely survive.
If damage from a strike is not severe, there are steps you can take to improve the chances of survival. Stressed trees attract several types of insects. An arborist should monitor for signs of these pests. Understand that it is not uncommon for struck trees to die a month or two after the strike so watch carefully as time progresses. Also, be sure to water damaged trees during droughts and fertilize to improve the growing environment.