In a forest near the town of Gryfino, Poland, there are 400 pine trees with unusually curved trunks. The trees’ trunks take a sharp, 90-degree turn and then curve to form a shape resembling the letter J.

How these trees all grew with an identical curve is a mystery. They are estimated to have been planted sometime in the early 1930s. During World War II, Gryfino was invaded and destroyed, and its residents had to abandon the town, according to reporting in the New York Times, including those who planted and knew the secrets of the forest.

Gary Coleman, an associate professor of plant science and landscape architecture at the University of Maryland, doesn’t know exactly what happened to these trees. However, he has a good idea about the science behind what might have caused the trunks to grow in such a weird way.

“It looks, to me, like a classic gravity response,” Coleman says. “Whenever the stem is horizontal to gravity, the plant has a mechanism through which it can reorient itself.”

Coleman estimates that sometime in the trees’ early lives, they were laid on their sides. “As you can see, the horizontal moment only occurs for a certain amount of time. It looks like it probably occurred when they were fairly young seedlings or maybe small trees, just a few feet tall,” he explains.

He recounts that during his time in the U.S. Forest Service, he came across trees in a Rocky Mountain area forest that were horizontal because of a small but strong storm. “There would be one or two acres where every tree was on its side but still alive. After a few years, it’s going to reorient itself,” Coleman says.

An environmental event like this kind of strong, localized storm could explain the Polish crooked trees. Trees may not be able to physically move because of changes in their environment — like animals can — but they have other responses. “They have a lot of different mechanisms in which they can sense environmental cues and adjust their growth to respond to these environmental factors,” Coleman says.

While there aren’t tree species that curve to this extent in nature, the eastern redbud tree is an example of a tree that has a weird shape that is naturally occurring. Its trunk grows straight but the redbud’s branches do not. A popular tree people buy for their yards, the redbud’s branches grow in different angles and make for an eye-catching, zigzag shape.

In the most likely case of the crooked trees, after somehow ending up in a horizontal position, their trunks began growing so that they were parallel to gravity. Trees have starch grains within their cells that cause this reorientation. “It’s actually the movement of these starch grains in these cells that triggers these responses,” Coleman says. “If the stem is horizontal, these starch grains are heavy and they’re pulled down in the cell by gravity.”

However, the question of how all 400 trees might have ended up horizontal in the first place is one that may never be answered.

“Whether it was man-made or whether it was a natural event like a storm or something, I’m not sure,” Coleman says.

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