Did these spruce trees really 'predict' a solar eclipse? Scientists are split

During an October solar eclipse in 2022, a team of scientists traveled to the Dolomites, a forested mountain range in Italy, to study spruce trees.

While the rest of the world was worried about buying solar eclipse glasses, timing telescopes to perfectly capture spectacular views of our sun and preparing for something profound, these researchers decided to spend time in the damp, woody and quiet air.

Fourteen hours before the eclipse began, the researchers recorded a heightened, synchronized electrical response from the spruces. And, after some analysis, the crew attributed the signals to the trees "anticipating" the upcoming eclipse in their own way. The team also concluded that older trees detected the eclipse first and communicated with younger trees via those electrical responses.

The team, led by Alessandro Chiolerio of Italian Institute of Technology, which included Monica Gagliano of Southern Cross University in Australia, then published a paper last year in the journal Royal Society Open Science detailing how they built custom sensors to measure electrical activity produced by the spruce trees and explaining what they found out about spruce tree communication.

However, a new opinion paper led by Ariel Novoplansky, a researcher and professor at Ben-Gurion University of the Negev in Israel, that was published Feb. 6 in the journal Trends in Plant Science, may have cut short the celebrations. Novoplansky and co-author Hezi Yizhaq call the original research into question, saying the team's conclusion doesn't necessarily come from the procedures they carried out.

In short, did Chiolerio and team really reveal that spruce trees can talk to one another before a solar eclipse — or is something else at play?

Well, Novoplansky's team concluded that no, the evidence Chiolerio and his team gathered does not suggest the trees anticipated the solar eclipse or communicated this or any other information to other trees.

Space.com covered the original research last year, and in light of the opinion piece, spoke with Novoplansky, Chiolerio and Gagliano to learn more about the debate.

We'll start with Chiolerio's perspective.

The Dolomites research

Back in 2022, in that mountainous study location, Chiolerio built custom sensors to measure the trees' "electrome," which refers to the total electrical activity within a living system. After attaching these "CyberTree" sensors to the spruce, the research team began to measure and record the trees' bioelectric signals.

"We saw that there was, in a certain moment, a synchronization of these waveforms," Chiolerio told Space.com. He likens the moment to an orchestra of instruments, suggesting "sometimes those instruments are playing perfectly in sync."

Indeed, he says on the day of the eclipse, the waveforms exhibited a behavior that was distinct when compared to the measurements on other days. "So, we ascribed the reason to the observation of the eclipse," he said.

The team gathered a number of environmental measurements during their research, including temperature, humidity, wind speed, rainfall and solar radiation, but they could not measure everything, such as cosmic rays and magnetic fields.

"We could not measure the environmental electrical fields that, for example, are associated with lightning," Chiolerio says. And Chiolerio also explained that, because the team didn’t measure everything, there could technically be a number of explanations for the synchronization waveforms emitted from the spruce trees.

Despite conceding that there could be other causes, Chiolerio stands by the work he and his team conducted in the Dolomites.

A new perspective

Novoplansky studies plant behavior. After he read Chiolerio's research paper, he says he disagreed with the findings and how the research was conducted, which led him to write the opinion piece.

"You should care about the education of people on the street and the awareness of the scientific community," Novoplansky says. "This is why I bothered and took the time to write this."

Novoplansky explains that there was a storm and lightning strikes that took place nearby and during the same time Chiolerio and his team recorded the tree's heightened activity. While Novoplansky does not definitively attribute the change in the trees' electrical activity to the storm and lightning, he says that this is a much more likely cause for the change in activity.

"This is much more parsimonious, which means it's easier to explain like that [compared to] the elaborate explanations that they give," Novoplansky says.

The older trees showed greater electrical activity compared to the younger trees, which Novoplansky says could also be explained by the lightning theory. This is because, he explains, older trees make "a bigger antenna to perceive this electrical activity."

Novoplansky also questions the trees' ability to anticipate a solar eclipse due to the minimal impact of the sunlight through a forest. "There is no real stress, nothing to get prepared for," Novoplansky said.

The eclipse was also partial, reducing sunlight levels by an average of 10.5% for only a couple of hours. Novoplansky likens this change in sunlight to that of clouds passing before the sun, which is the rule rather than the exception for these trees. Because the change in solar activity was minor, he believes the eclipse was "not sufficient enough for the trees to discern such a situation."

Furthermore, Novoplansky cites the unique trajectories of solar eclipses. While plants can "remember" past experiences, he says it doesn't make sense for the trees to remember a past solar eclipse, because it occurred at a separate location.

Reacting to criticism

Novoplansky goes as far as to call the original research "pseudoscience," but Chiolerio and Gagliano disagree. Chiolerio points out that the research was grounded in measurement.

"I wanted to be totally transparent, so that anybody in the world could replicate what we did," Chiolerio said. "You can find there the schematics of the circuits we developed, and also of the architecture of the system, including the firmware. Everything is there."

Gagliano, who also studies plant behavior, views the opinion piece as a mixed critique. "It is fair in emphasizing what our field dataset cannot establish on its own," she says. "Most importantly, it does not uniquely identify a causal mechanism, and synchrony in an observational dataset is not, by itself, proof of interplant communication. Those are standard limits of field observations, which we acknowledged."

But Gagliano wants people to understand the separation between observation and hypothesis. "What we reported is an empirical observation: a structured electrical-signal pattern and increased synchrony occurred in the eclipse window," she says. "The opinion piece proposes weather/lightning as a plausible alternative hypothesis, which should be tested explicitly."

Chiolerio acknowledges that lightning could be the explanation for the shift in the electric activity. But without testing this theory in the field, there's no way to know for sure.

"I would like people to come to me and say, 'Let's do an experiment together,’ Chiolerio continued. Conducting a similar experiment during a total eclipse could possibly yield different results. "This year in Spain," he says, "there will be a total eclipse, so we could do that."