Trees growing amid rocks, particularly in harsh environments with heavy snow, strong winds and/or arid conditions, often adopt a growth pattern where the xylem spirals around the phloem portion of the trunk in a manner reminiscent of a barber pole. This phenomenon is most readily seen when the bark is removed from the tree.
Why would a tree “twist” in such a manner. One reason mentioned in the literature is that this spiraling distributes water and nutrients evenly on all sides of the tree permitting a full, well-formed crown. All the roots of a tree anchored on rocks may not have access to soil. If the xylem, which carries water and nutrients, runs straight upward, those parts of the tree with roots that are not in soil may not get the necessary food and water to develop properly. By spiraling around the tree the xylem reaches all sides of the tree nourishing all the branches.
Alternatively, a tree with its xylem growing in a spiral pattern is less stiff than a straight-trunk tree and bends more easily. This trait allows the tree to discard snow from its branches without damage and makes the tree more resistant to breakage from high winds. (There are several papers filled with calculations only a physicist could love demonstrating how spiraling xylem increases the flexibility of a tree.)
The spirals can grow to the left or to the right and can reverse directions during the growth of the tree. Most spirals are at approximately a 30° angle but that varies. The physiological triggers for this growth pattern are still not understood.
These spiral growth trees were at the Lava Cast Forest in Central Oregon. I believe they are junipers, but since they were dead and without bark I cannot be certain.
I think these “ghost trees” are beautiful – and fascinating.