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College of Science and Mathematics

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Do Cook Pines Pine for the Equator?

Perhaps the Cook pine never wanted to leave New Caledonia. In a recent article in the journal Ecology, botanists from California Polytechnic State University reveal a novel behavior of the Cook pine — it always leans toward the equator. This behavior has never been observed in a plant before.

Most trees correct any lean resulting from gravity or the position of the sun as they grow, so when biology Professor Matt Ritter noticed that all the Cook pines he’d seen leaned south, he got curious. Ritter called a colleague in Australia to see whether he’d made similar observations.

“He said, yeah, they all lean north. And I said, you mean south,” Ritter said.

To untangle this puzzle, Ritter enlisted the help of Professor Jenn Yost and graduate student Jason Johns, who began a worldwide exploration of Cook pines, coordinating the measurement of 256 trees on five continents. The pattern held. Trees in the northern hemisphere all leaned south, while their counterparts in the southern hemisphere all leaned north.

In another interesting twist, the trees tilt closer to the ground the farther they are from the equator.

Maybe Cook pines all over the world are trying to return home. The Cook pine originated in New Caledonia, an archipelago in the South Pacific not far from the equator. The research team doesn’t yet know what causes this behavior. Possible hypotheses include a genetic mutation in the tree’s wood formation or the way the tree reacts to gravity.

“The observation of patterns like this is incredibly important scientifically speaking,” Ritter said. “These trees have always done this, but no one’s investigated it until now.”

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