Lightning strikes can cause diseases and pests, leading to the need for secondary management practices and the removal of trees. This document outlines the damage caused by lightning to trees and emphasizes the importance of preserving and protecting lightning-struck trees for various reasons. Apart from enhancing the beauty of the neighborhood, these trees provide natural habitat for wildlife, as well as screening and shading for neighbors, while also increasing property values. While some of these benefits will occur in urban areas, the majority of lightning strikes are likely to happen in rural forests.
Figure 1 demonstrates that counties in the southern region experience a higher frequency of lightning strikes compared to those in the northern region. The entire state of Alabama encounters a period of active thunderstorm activity, but the southern counties encounter a greater number of lightning strikes than their northern counterparts. Approximately 60,000 trees in the state are affected by lightning strikes each year, which accounts for roughly 6 percent of all lightning strikes that occur. It is estimated that Alabama experiences around 202 days with thunderstorms, resulting in nearly 1 million cloud-to-ground strikes. On average, a thunderstorm produces one lightning strike every 30 seconds during a span of 50 minutes.
Lightning, also known as leaders, forms long chains in the clouds when negative charges from the base of a storm reach down. This process is known as a lightning strike. Figure 2 shows the upward movement of positive charges drawn by the negative charges in the form of streamers. Streamers are most commonly observed on the tallest geographic features, such as trees, buildings, boats, and mountains. When two paths meet, a rapid exchange of charges occurs, generating heat and light, and creating an electrical connection.
It is not uncommon to see multiple lightning-struck trees within small geographic areas. It is also important to consider the site’s history, as some areas are naturally more prone to lightning strikes than others. The tallest trees on hilltops or in open fields often have the greatest potential for strikes. Trees are often the tallest structures and decent conductors, as they are natural lightning rods. However, wood is generally not a good conductor of electricity, as it lacks the moisture in the form of sap and water that attracts lightning. Lightning typically follows the path of least electrical resistance, which is the best available conductor.
Lightning carries up to 100 million volts and can travel through the water-conducting woody xylem or the deeper layers of the bark, conducting sap through the phloem. It can affect a portion of a branch or trunk, or skip down to the roots of the tree from the top. Lightning can strike a tree multiple times or once, causing the wood and bark fibers to explode and generating steam by boiling the sap and water at these extreme temperatures, which can reach up to 27,760 degrees Celsius (50,000 degrees Fahrenheit), which is five times the temperature of the sun.
Several days following the occurrence, trees may exhibit a sudden decline as their leaves wither and change color. In such instances, there may also be concealed harm as the intensely heated electrical discharge disrupts operations in substantial sections of the main stem or underground parts. The initial harm within the trees includes deceased tissues along the trajectory of the lightning strike and the exposure of the inner woody tissues to decay and insect invasions. The extent of damage can range from the bark being forcefully expelled along a narrow band (as shown in figure 3), revealing the inner wood, to more severe scenarios (as depicted in figure 4), where trees lose their bark entirely or develop deep crevices (as illustrated in figure 5).
Managing lightning-struck trees with a multifaceted approach, we advise taking preventative treatments to ward off opportunistic insects which can cause further damage. While waiting is an option, it is evident that damage becomes visible in the interior of the crown before signs of damage become outwardly visible, so pruning or removing the tree may be necessary after several weeks of waiting.
Preventative Treatments for Insects
Lightning strikes can often result in trees being stressed and damaged, attracting insects that can further kill them. These insects emit volatile compounds that attract pests, and the bark, which protects the interior woody tissues from opportunistic decay and insect infestation, can be stripped away by lightning strikes. Lightning strikes can also push trees into a state of drought-like stress, damaging their water-conducting vessels and sap flow.
If populations of beetles are allowed to spread and grow outside the circumference of the entire death tree, the lightning scar is likely to become a habitat for them. Both groups of insects bore into weakened trees and inoculate them with a fungus that plugs up the water-conducting vessels in the trees. Several species of pine beetles, including the black turpentine beetle and the southern pine beetle, are likely to be problematic, especially the ambrosia beetle, which can be problematic in hardwood trees.
Some cases may find it advantageous; however, the effectiveness of insecticide treatments as a preventative measure against lightning damage cannot be fully understood, which has sparked some controversy. To ensure the protection of trees, it is crucial to make applications as soon as possible, ideally within a few days or the next day. The timely application is critical as beetles can begin infesting trees within days. Instead of attempting to kill the beetles as they bore into trees, preventative treatments must be applied to kill the beetles. Unfortunately, there are no products labeled to control these groups of beetles from entering trees at once.
Apply the insecticide till the height of the breast at a diameter of 28 inches under smaller trees, spraying only the area around the scars. Large trees with small lightning scars would be the exception, where it would be possible to inject systemic injectable products such as Benzoate Emamectin into the trees (as shown in table 2) or spray the tree trunks with contact insecticides like Permethrin and Bifenthrin. This process may require the assistance of a professional arborist.
The drawbacks and issues with the use of contact pesticides are threefold:
The restrictions on these goods are as follows:. Systemic goods depend on the water- and sap-conducting vessels to transport the insecticide throughout the canopy, which can offer exceptional long-term defense. Injectable systemic goods offer greater long-term defense, occasionally lasting up to 2 years, and will safeguard the entire tree (table 2). Reapplication of contact insecticides should occur every 1 or 2 months following lightning strikes. These insecticides are easily accessible.
Regardless of the item you select, adhere to the label guidelines and don the suitable personal protective gear.
Bark Tracing
If there is a need to enlarge the wound, the tracing bark technique can be used to carefully remove any loose or broken bark from the tree’s scar. This technique is considered a suitable option for tree preservation, as it involves the use of a sharp knife to remove the jagged and loose bark from the edges of the scar.
Tree Damage Assessment
The potential for future decay and larger injuries can be caused by concerns about the structural integrity and safety (table 1). The website www.Aces.Edu offers a “Step-by-Step Guide to Examining Your Tree for Safety” for a list of tree species and their ability to withstand decay after being damaged by storms. These factors, including the type of tree, its health, and the extent of the damage, can affect the inevitable decay and the tree’s ability to grow around wounds and respond to them. When evaluating trees, it is crucial to consider how they will recover from wounds and the extent of the external damage. There are no specific guidelines available for determining a tree’s chances of surviving a lightning strike.
Evaluate the breadth, profundity, and vertical range of the lightning impact within the treetop. Trees may fragment, leap from limb to limb, descend in a spiral along the trunk, or traverse a straight trajectory. If one-third or more of the width exhibits notable lightning marks and is forcefully obliterated, promptly contemplate eliminating the tree (figure 6). Likewise, if the tree is partially or completely severed, extract the tree (figure 4). In both of these instances, the likelihood of failure will progressively rise as the tree continues to deteriorate due to decay.
When considering how much the trunk is damaged, it is likely that the living tissue on the same side of the tree will be dead. Sometimes, a tree will have multiple scars. These scars can make them prone to failure and structural problems over time, and they are likely to cause significant decay in the future if the trunk has scars with no bark covering more than one-third of its diameter from lightning.
These trees, which are often used in driveways, busy streets, and near high-value homes, should be removed. The woody tissue of these trees will have structural integrity loss and decay issues due to deep cracks extending into it. Trees with lightning scars that are less than one-third of the tree’s diameter are good candidates for preventative treatments and observation.
Irrigation
Watering can assist the wounded tree, especially during arid spells, as the roots and water-carrying channels may have sustained damage. Adequate moisture should be provided by administering a thorough watering, ensuring that the upper 6 to 9 inches of soil remain moist. The frequency of watering should be restricted to once or twice a week, and the irrigation should cover the tree’s entire root area or as much of the drip line as feasible.
These trees are designed to provide an exterior path for lightning to travel from the outside ground of the tree (figure 11) to the home, as copper and brass are entirely made of and remarkably similar in providing lightning protection. They are prone to lightning strikes and are often the tallest structures in the average landscape.
A standard lightning protection system will include the following:
To determine how much equipment is needed, consider the size of both the structure and the tree. For example, each terminal air and cable fork will be topped with a tree crown, and a single rod will be needed for both ground and cable. Additionally, one terminal air and a single cable may require a diameter of less than 35 feet, with a canopy height of less than 36 inches and a trunk diameter of less than 36 inches.
To properly protect a large tree, it is necessary to install ground rods, cables, and multiple air terminals. The primary conductor is connected to extra air terminals to accommodate the needs of a tree with a crown that exceeds 35 feet in width.
There is a significant risk of lightning strikes in areas with dense tree coverage or historically significant trees. Trees hold a high value for their ability to protect against lightning, so it is typically recommended to use tree protection systems. These systems need to be installed correctly by a well-trained tree specialist and are typically made of copper, making them quite expensive.
As with all highly skilled tree work, we recommend ISA Certified Arborists with training in the craft to install a protection system.
Auburn University has specialists in pests, home and garden care, commercial horticulture, natural resources and wildlife, and forestry. They also have extension agents who specialize in regional arborticulture and forestry community. Jacobi Jim and Jack Rowe are the specialists in grounds maintenance and horticulture, while Arnold Brodbeck is the specialist in arboriculture and forestry for the extension department.
In May 2023, the care of trees struck by lightning will be discussed in FOR-2134.