Lightning strikes represent a powerful natural disturbance that instantly compromises the health and structural integrity of a tree. A typical cloud-to-ground strike carries an immense electrical charge, which directly impacts the tree’s internal systems. While a direct strike hits the tree itself, proximity damage, such as a ground current, can also injure the root system even if the trunk shows minimal external signs. Understanding the specific signs of a lightning strike is the first step toward assessing the tree’s survival probability and determining the necessary care.
How Lightning Strikes Damage Trees Internally
Internal damage results from the rapid superheating of moisture within the tree’s tissues. A lightning bolt can generate temperatures up to 50,000 degrees Fahrenheit, causing the water and sap in the conductive layers to instantly vaporize. This conversion to steam creates explosive pressure that ruptures the wood fibers and forces the bark outward.
The electrical current typically follows the path of least resistance, which is just beneath the bark in the cambium layer where water and nutrients are transported. When the cambium is destroyed, the tree is essentially girdled, disrupting the flow of water (xylem) and sugars (phloem). Even if the exterior damage is minimal, the internal vascular system can be compromised, leading to a delayed decline that may manifest weeks or months later. High-resin species, such as pines and spruces, are particularly susceptible to this internal heating and explosive damage because their internal composition makes them more conductive.
Identifying the Visual Signs of a Lightning Strike
The most recognizable sign of a lightning strike is a long vertical scar where a strip of bark has been blasted away from the trunk. This scar often follows a linear or spiral path down the trunk, sometimes extending from the crown to the ground. In severe cases, the pressure can cause the trunk to splinter, resulting in deep cracks or the complete splitting of the tree.
Other visual indicators include scorched or wilted foliage, which appears brown or yellow soon after the strike due to the disruption of water-conducting tissues. Look for blackened or charred sections of wood along the trunk or branches where the intense heat burned the surface. Subtle signs of root damage may be visible on the ground around the tree’s base, such as cracked soil or the sudden death of small plants. Broken or exploded branches scattered around the base can also signal a strike that traveled through the canopy.
Assessing a Tree’s Chances of Survival
The prognosis for a lightning-struck tree depends primarily on the extent of damage to the trunk’s circumference. If the lightning scar has destroyed conductive tissue along more than one-third of the circumference, the tree’s ability to transport water and nutrients is severely compromised. Damage exceeding this threshold raises the risk of future decay and structural failure, often necessitating removal if the tree is near a home or structure.
The tree species and its health prior to the storm are also factors in determining survival. Healthy trees are more resilient and better equipped to compartmentalize the damage than those already stressed by disease or poor growing conditions. Since internal damage can take time to become apparent, a tree may appear stable but decline suddenly months later as the effects of vascular damage or secondary pest infestations take hold. A definitive assessment often requires a period of observation, sometimes lasting up to a full year, to see if the tree can successfully respond to the injury.
Immediate Safety and Post-Strike Care
Safety must be the first concern after a tree is struck by lightning, as damaged trees present a hazard. Homeowners should immediately check the canopy for broken branches that may be hanging precariously, often called “widowmakers,” and assess the trunk’s stability before approaching the tree. Consulting a certified arborist is recommended for a professional risk assessment, as they evaluate the extent of both visible and hidden damage.
Immediate care involves removing any severely damaged or hazardous limbs using proper pruning techniques. The tree will be under stress, so providing supplemental watering is beneficial to prevent drought stress, but aggressive fertilization should be avoided. If loose bark remains but the underlying cambium tissue is still moist, some arborists may temporarily secure it to facilitate healing. Otherwise, the wound should be left open to let the tree form a natural callus.
Installing Lightning Protection Systems
For historic trees, high-value specimens, or those situated near structures, a lightning protection system (LPS) offers a preventative measure against damage. The system functions by providing a conductive, low-resistance path to safely divert the electrical charge away from the tree’s tissues. This is accomplished through the installation of air terminals—pointed metal rods positioned at the top of the canopy to intercept the strike.
The current is channeled down the trunk via conductor cables, typically copper or aluminum, which are secured to the tree but bypass the living wood. These conductors lead to a grounding system, consisting of metal rods buried deep in the soil, which dissipates the electrical energy into the earth. A properly installed LPS ensures that the lightning follows the metal, which is a better conductor than the tree’s cellulose, protecting the tree’s structural integrity and long-term health.