Doing the Twist

10-01-1998 // NWF Staff

Something strange happens to conifers in the Northern Hemisphere as they age: Their grain gradually spirals to the right, up the tree. In the Southern Hemisphere, however, tree spirals tend to be aimed to the left. Research has indicated these tendencies are inherited, but why? What is the evolutionary advantage?

Norwegian foresters Sondre Skatter and Bohumil Kucera speculate in part that over time, the trees have responded to being broken and twisted by the wind. "Conifers are exposed to a prevailing torque in the counterclockwise direction in the Northern Hemisphere and a clockwise torque in the Southern Hemisphere," points out Skatter. That´s because more branches and needles grow on the sunny side of trees--the south side for trees in Earth´s northern half and the north side for those on the other half of the globe. Over time, natural selection may have favored trees with grain that helps the foliage cope with the wind, which tends to come from the west. "Trees with opposite spiral direction tend to snap during storms," he explains. "At least that´s the theory."

Trees also seem to respond to the moon. In separate research by Swiss and Italian scientists, trees were found to rhythmically swell and shrink in a 25-hour two-peaked cycle that closely corresponds to that of tides. That could explain an old belief in many cultures around the world that newly cut wood will dry fastest if trees are chopped before a new moon, which signals the weakest coastal tide of the month.

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