In a widely publicized study, Chiolerio and colleagues had reported that the trees appeared to "anticipate" the approaching eclipse, interpreting their bioelectrical signals as evidence that they were preparing for the temporary dimming of sunlight. The new analysis, published February 6 in the journal Trends in Plant Science, challenges that interpretation and proposes a simpler explanation rooted in established plant and atmospheric science.

"To me, this paper represents the encroachment of pseudoscience into the heart of biological research," says first author Ariel Novoplansky, an evolutionary ecologist at Ben-Gurion University of the Negev in Israel. "Instead of considering simpler, well-documented environmental factors, like a heavy rainstorm and a cluster of nearby lightning strikes, the authors leaned into the more seductive idea that the trees were anticipating the impending solar eclipse."

Plant biologists have long known that vegetation can detect and respond to changes in light, moisture, temperature, and other environmental cues, and in some cases can even adjust in advance to predictable stresses or competition. However, Novoplansky and co-authors argue that such anticipatory behavior only evolves when the predicted event poses a substantial challenge and is tightly linked to reliable cues that organisms can learn or encode.

In this case, the partial solar eclipse over the Dolomites was brief and relatively weak in intensity. According to the new analysis, the eclipse reduced available light by only about 10.5 percent over roughly two hours, and during that window the sunlight levels remained roughly double what the trees could actually use for photosynthesis. The authors note that ordinary variations in cloud cover at the site routinely cause much larger and more frequent swings in light quality and quantity than the eclipse did.

"The eclipse only reduced light by about 10.5% for two short hours, during which the level of sunlight was approximately twice what the trees could practically use," says Novoplansky. "Frequent fluctuations in cloud cover at the study location change light quality and quantity by much bigger amplitudes."

Even if the eclipse had represented a strong enough environmental stress to warrant anticipation, the trees would still lack a plausible mechanism to foresee its timing, the authors argue. The event was the 53rd eclipse in the Saros 124 sequence, a family of eclipses that recur every 18 years, 11 days, and 8 hours. Chiolerio et al. reported that older, larger trees showed stronger electrical responses than younger trees and suggested that this might reflect experience with earlier eclipses and some form of inter-tree communication.

The new paper counters that each eclipse in such a sequence differs in its path, magnitude, and duration, which undermines the idea that prior exposure could train trees to recognize or anticipate a specific future event. The authors also point out that the gravitational changes during a solar eclipse, proposed as the signal to which the trees were responding, are similar in scale to the routine tidal variations that occur with every new moon and thus provide little unique, actionable information.

The critique also highlights statistical and sampling limitations in the original work. Chiolerio and colleagues based their conclusions on measurements from only three living spruce trees and five stumps, a very small sample size for drawing broad inferences about forest-scale behavior or communication. Novoplansky and co-authors caution that strong claims of coordinated, anticipatory responses should rest on much more extensive and robust datasets.

Finally, the authors urge both researchers and the wider public to be wary of dramatic interpretations of plant electrical activity that are not firmly grounded in evidence. "The electrical activity of trees is a real phenomenon but it's still a nascent field of inquiry," says Novoplansky. "The idea that variations in electrical signals, observable even in dead logs, might encode memory, anticipation, or collective responsiveness requires a few extraordinary leaps, none of which were supported in the study. The forest is wondrous enough without inventing irrational yet superficially fantastic claims of anticipatory responsiveness or communication based only on correlation."

The opinion article, "Eclipse of reason: Debunking speculative anticipatory behavior in trees," appears in Trends in Plant Science and was supported by the Israel Science Foundation and the V. Kann Rasmussen Foundation.

Research Report:Eclipse of reason: Debunking speculative anticipatory behavior in trees

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