In a strange discovery they made a few years ago, a group of researchers found that Cook pine trees lean toward the equator wherever they are on Earth.
The slope of the Cook pines (Araucaria Columnaris) is clearly visible. In fact, according to the researchers who discovered the equatorial slope, “when grown outside its natural range, this species has a marked weakness and such a pronounced slope that it is often used as a defining feature for this species.”
Matt Ritter, now director of the Cal Poly Plant Conservatory, was writing about pines for a book when he noticed that the trees he was examining all appeared to be leaning south, New Scientist reported. Ritter began calling his colleagues around the world to see which way the pines were leaning, and soon learned that they were all leaning towards the equator.
To further study the phenomenon, Ritter and his team took measurements of 256 trees at various latitudes on five continents.
“We have shown that the slope of Cook pines is not random: trees in the Northern Hemisphere lean south and those in the Southern Hemisphere lean north,” the team wrote in their work. “Also, the magnitude of the slope is more pronounced at higher latitudes in both hemispheres.”
On average, trees lean 8.05 degrees toward the equator, but the slope becomes more pronounced as they move away from the equator, with only 9 percent of trees declining from the projected direction.
Trees grow vertically, often in response to the opposing effects of gravity (gravitropism) and light (phototropism). “The leading hypothesis for the molecular mechanism of gravitropism is that precipitation of amyloplasts on actin microfilaments activates a signal transduction pathway that results in asymmetric transport of auxin in the root and causes it to self-correct in parallel with the gravity vector,” write the study’s authors.
In more challenging environments, trees can bend in different directions as they grow towards available light. However, while young plants may grow towards the Sun, they tend to correct themselves as they grow due to the influence of gravity. It’s not yet clear why Cook pines have a distinctive slope, but the team suggests it could be a useless, maladaptive quirk in their genetics or something similar.
The team notes that the phenomenon needs further study, as “plants respond to their global environment in a way that is not yet fully understood.”
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