For some trees, acting as lightning rods helps them survive

Getting hit by lightning is not usually good. But one tropical tree seems to invite heaven’s wrath. In fact, it can benefit from a powerful electric jolt or two.

The height and broad crowns of almendro trees (Dipteryx oleifera) act as natural lightning rods. They not only can survive a powerful bolt of lightning, but actually attract it. In a dense jungle, such zaps can even give the tree a competitive advantage. Why? That lightning will hurt its foes.

The finding comes from a years-long study in Panama’s Barro Colorado Nature Monument. Using drones, an array of cameras and ground teams, scientists studied lightning’s overall impact on local trees.

The group expected the zaps would harm trees — always. But it soon became clear that one species got a boost. The occasional shock therapy tended to fend off rival trees. The high-energy bolts also killed off potentially parasitic vines, known as lianas, that could have strangled an almendro.

Indeed, the competitive advantage from these strikes increased the reproductive success of those trees by 14 times.

Researchers shared their new findings in the May New Phytologist.

Tallying the death tolls

Study leader Evan Gora works at the Cary Institute of Ecosystem Studies in Millbrook, N.Y. This forest ecologist recalls just when the idea of a link between lightning and the almendros’ success first hit him. It was after an especially powerful 2019 lightning bolt. After it struck one of these trees — it “looked like a bomb went off,” he says.

The zap damaged an amazing number of surrounding trees, too — 115 in all. Half of those died within two years. So did every liana vine that had covered the zapped almendro.

And the tree that was struck? It survived unscathed. It remained tall and healthy even as lightning had removed its direct competitors.

Afterward, Gora recruited a team to investigate his hypothesis of a lightning benefit for some trees.

This group documented the fate of 93 trees hit by lightning. Among them were nine almendros. After two years, every zapped almendro tree was doing fine, Gora reports. In fact, they were thriving. But 56 percent of the other species that had been hit are now dead.

Shock therapy against lianas

Apart from a few ruffled leaves, almendros aren’t hurt by lightning. The electric shock, however, will fry most of the lianas growing up them.

These vines sprout everywhere throughout the jungle. And they pose a real threat to trees. At a minimum, they cut off light to the trees that they ascend. They also can steal nutrients from large trees.

And a liana may not climb just one tree. It can send up vines that connect to branches on neighboring trees. So if lightning strikes an almendro, the deadly current can spread through lianas to a host of neighboring trees.

This fallout from lightning can free up space, light and nutrients for an almendro. On average, about nine nearby trees were killed by each almendro strike.

In fact, growing next to an almendro truly seems hazardous to its neighbors since the new data suggest almendros actively attract lightning. How? They tend to grow taller than their neighbors. Their upper canopy also grows wider than that on other trees. In the end, this makes an almendro 68 percent more likely to be struck by lightning.

One almendro tree was struck twice in five years, Gora’s group found. His team now estimates that the typical tree will be struck an average of five times over its 300-year average lifespan.

One big mystery remains

Connecting the dots between lightning and the pruning of almendro competitors was not easy. It required the right tools and surveys over a long time.

“A lightning strike lasts a few milliseconds,” Gora notes. “Then it takes months for the trees and lianas to die.” So it can be hard to establish the full impacts, he says, “unless you happen to be tracking the lightning strikes.”

Still a mystery: Why doesn’t lightning kill almendros?

One possibility is that the tree’s wood has low electrical resistance. That might let it safely conduct current to the ground without suffering an excessive buildup of heat. Another hypothesis: The structure of the tree’s crown may direct electricity away from the trunk — and toward its neighbors.

“It’s really difficult” to understand all the biological and physical steps that take place when lightning hits trees, says Bianca Zoletto. “It would be fascinating to be able to say something more on that,” this ecologist notes. But for now, she points out, “that goes a bit more in the physics side, rather than the ecological side, of the study.”

Zoletto, who works at Wageningen University & Research in the Netherlands, didn’t take part in new study. But she, too, has been studying how lightning and other high-voltage electrical phenomena affect tropical forests. And, she now stresses, recruiting the help of physicists could help biologists uncover what happens when a tree is struck by lightning. They’re all curious how the almendro avoids getting fried by each thunderous zap.