Lightning strikes involve immense electrical power, instantly overwhelming a tree’s biological systems. The energy surge seeks the path of least resistance, typically the moisture-rich tissues just beneath the bark. This results in a sudden, massive transfer of heat, leaving immediate physical evidence on the exterior of the trunk and branches.
Immediate Physical Signs on the Trunk and Branches
The most characteristic sign of a lightning strike is the long, continuous “lightning scar” etched into the tree’s bark. This vertical or spiraling groove is created when the intense heat instantly vaporizes the water and sap in the tree’s outer layers. The sudden conversion of liquid to steam causes an explosive force that shatters the bark outward, peeling it away in long strips to expose the raw wood beneath.
The path of this scar often follows the grain of the wood, sometimes twisting slightly as it descends the trunk. Splintered wood and scattered pieces of bark at the base of the tree are common, indicating where the explosive pressure was greatest. In some cases, the strike may be so intense that it splits the trunk entirely or violently shatters major limbs, leaving branches with a torn, shredded appearance rather than a clean break.
Burn marks, appearing as blackened or charred areas, may be visible near the point of entry, often at the top of the tree, or where the strike exited near the root flare or on a lower branch. However, a lack of charring does not rule out a strike, as the current may have passed through the wet outer bark, or the damage may be entirely internal.
Delayed and Hidden Damage Beneath the Surface
While the bark scar is the most obvious sign, lightning often inflicts significant damage that is not immediately visible and may take months to manifest. The electrical charge travels through the tree’s vascular system, specifically the water-conducting xylem and the cambium layer just inside the bark. Even a narrow external groove can destroy a wide band of these internal tissues, disrupting the transport of water and nutrients.
This internal injury leads to delayed symptoms, such as the wilting, browning, or sudden dieback of leaves and needles, which may not appear until weeks or months after the event. The electrical energy also disperses into the soil upon exiting the tree, often damaging or killing large sections of the root system without any above-ground indication. Extensive root damage compromises the tree’s stability and its ability to absorb moisture, leading to a slow, irreversible decline.
The exposed wood of the lightning scar creates a large, open wound, leaving the tree vulnerable to secondary invasion by pests and pathogens. Stressed trees attract opportunistic insects, such as wood-boring beetles, which introduce fungal infections that cause decay. This compounding damage can ultimately lead to the tree’s demise.
Safety Concerns and Professional Assessment
Approaching a tree immediately after a lightning strike requires extreme caution, as the structural integrity may be severely compromised. Unstable, broken branches, often referred to as “widowmakers,” may be lodged precariously in the canopy and can fall without warning. It is also advisable to maintain a safe distance, particularly in urban settings, as the strike may have caused a side flash to nearby power lines or structures.
The tree’s long-term prognosis depends largely on the extent of the damage to its circumference and its ability to compartmentalize the injury. Trees that have lost bark on more than one-third to one-half of the trunk’s circumference are often unlikely to survive because the continuous vascular system has been interrupted. The species, age, and overall health of the tree prior to the strike are also significant factors in recovery.
When to Call an Arborist
If the tree is large, valuable, or located near a structure, a professional assessment by a certified arborist is necessary. An arborist can safely remove hazardous hanging limbs and accurately evaluate the depth of the internal damage and the percentage of compromised cambium.
Observing Recovery
Waiting a full growing season before making a final decision on removal allows time to observe the full extent of the delayed symptoms and the tree’s natural response to the trauma.