When tested for the ability to bend before breaking, spiral-grained sticks break under the same force as straight-grained sticks, but spiral-grained samples performed differently than straight ones before breaking. Spiral-grained materials deflect (or bend) more than straight-grained materials. During deflection of straight-grained materials, the side nearest the force is compressed while the opposite side is stretched, putting it under tension. In contrast, spiral-grained materials transfer the compression and tension forces along the spiral to the other side, thereby equalizing the stresses.
Spiral structure of Scots pine reduces stress from wind.
Artist: Emily Harrington. Copyright: All rights reserved. See gallery for details.
“…increasing the mechanical resistance by means of fiber spirals, which are easier compressed and stretched without breaking, is also applied in the spiral growth of tree trunks. For inexplicable reasons, many trees start growing spirally under strong pressure from wind and snow, as is often encountered in the mountains or in subarctic regions. Under such circumstances the wood fibers may deviate up to 30° from the vertical direction of growth. Since this spiral growth offers the plant better protection against mechanical destruction, it may well be regarded as a kind of defensive reaction.” (Tributsch 1984:28-29)
“Compared with straight-grained trees, spiral-grained stems and branches bend and twist more when exposed to strong wind, in this way offering less wind resistance and being less likely to break. Through the bending and twisting, snow slides down from branches rather than breaking them…” (Kubler 1991:125)