Wood grain can spiral either clockwise or counterclockwise. Which direction it spirals likely depends on how the tree's growth layer arranges tiny fibers as it builds new wood. You’ll encounter this in species like Scots pine, Sitka spruce and Douglas-fir.
What makes a tree a righty or a lefty? Scientists can’t say for sure, but they have some ideas! Just as with humans, part of the answer appears to be genetics.
But a tree’s environment also plays a role. As trees grow, they experience twisting forces from wind and from the uneven weight of their own crowns. In some species, the spiral direction can even change as it gets older.
Why have trees evolved this twist? It may help them survive strong winds.
In a tree with perfectly straight grain, bending concentrates stress along a single vertical line of wood fibers, so the trunk will split under heavy gusts. But a spiral grain spreads those forces around the trunk, distributing stress across many fibers.
Instead of behaving like a rigid beam, the trunk acts more like a flexible cable, able to bend and twist without breaking.
So, on your next forest hike, look closely. Some of those seemingly straight trees may actually have a quiet twist.
