South Jersey thunderstorms come through hard. When lightning lands on a tree, the sap inside the wood boils in an instant — and the pressure blows the bark off the trunk at speed. One piece on this poplar made it through a nearby window.
Most homeowners have never thought about what physically happens when a lightning bolt lands on a tree. It’s worth knowing — both because it’s genuinely interesting biology, and because the answer changes how you respond when you walk out the morning after a storm and see a 60-foot tulip poplar with bark blown off twenty feet up the trunk.
View from the Field · Paul Biester · Tree Awareness
“Here in South Jersey we’ve been having a lot of thunderstorms roll through, night after night. Well, last night this big old poplar suffered a big lightning strike. When lightning hits a tree, it basically boils the sap in an instant, and it blows bark off the tree. This poor old girl took a shot — in fact, it threw a piece of bark all the way through that window right there. You can see that little brown piece, that tan piece in the lower right corner is a piece of bark that broke the window. So you don’t want to be around these when that happens. Lightning damage is a dangerous thing.” Paul Biester · NJ LTE #408
Lightning takes the path of least resistance to the ground, and on a tree that path runs through the most water-rich tissue available. The tree’s xylem — the tube system carrying water from the roots to the canopy — is full of liquid sap. When the bolt’s current passes through it, the sap doesn’t just heat up. It superheats to thousands of degrees in milliseconds and flashes from liquid to steam. The volume change is massive. The expanding steam has nowhere to go fast enough, and the bark above the heated zone is the weakest containment. So the bark blows outward.
What you see on the trunk afterward is a long vertical strip of exposed cambium, often spiraling around the tree the way the grain runs, sometimes blown clean off in plates the size of dinner plates. On the poplar in this video, one of those plates came off with enough force to travel and break a window in a nearby structure.
The outcome depends on three variables. Species. Trees with high natural moisture content and conductive bark patterns — oaks, poplars, tulip trees, sycamores — are statistically more likely to be hit and more likely to be killed. Trees with thicker, less conductive bark — beech, birch — can sometimes ride a strike with surface damage only. Path of the current. If the bolt traveled down the outside of the tree (a “side flash” on wet bark), the cambium layer can survive. If it traveled through the conductive xylem inside the trunk, the cambium gets cooked along its full length and the tree is structurally finished. How much of the cambium is destroyed. A tree can survive losing a strip of cambium on one side. Lose more than about 50% of the circumference of living cambium and the tree can’t move enough water to support its canopy and decline becomes irreversible.
Three things, in order.
Don’t approach the tree until you’ve assessed for hanging hazards. A lightning-struck tree often has limbs that have been internally damaged but are still attached. They can fail without warning hours or days after the strike. Stay out of the drip line. Keep kids and pets away.
Get an arborist on site. A qualified visual assessment will tell you whether the tree is structurally salvageable or whether the right call is removal. The decision depends on cambium loss, evidence of internal damage, the tree’s target zone (what would it hit if it fell), and species-specific recovery rates.
Don’t prune yet. The tree’s response to the injury — compartmentalization, defensive chemistry, redirecting resources — takes weeks to express. Pruning before that response stabilizes can set the tree back further. The exception is broken or hanging limbs that are an immediate hazard, which need to come down.
The story doesn’t end with this clip. The lightning-struck poplar Paul filmed here became a hazard tree over the structure on Cooper Street in Woodbury, and Tree Awareness brought in a 55-ton crane and a multi-trade team to remove it later that summer. See the case study on the removal →
