Spiral Fibers Strengthen Tree Trunk

a tall Scots pine tree on a green hill agains a bright blue sky

Biological Strategy

Pines

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Manage Shear

The effect of shear stress on a living system is parallel internal surfaces sliding past each other. Slippage occurs in parallel with the force. Think about holding two wooden boards on top of each other and sliding one to the right and the other to the left. This may be easy until you add glue, which increases their shear strength and makes them harder or impossible to slide. Shear can occur in solids, liquids, and gases. Living systems must increase their shear strength to overcome these types of forces. For example, darkling beetles lock their wings together in flight to prevent lateral movement by using many small hairs on each wing. These hairs interlock to provide shear strength, just as two hair brushes put together would be difficult to slide past each other.

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Protect From Wind

Wind subjects living systems to various forces, such as compression, twisting, turbulence, and tension. These forces put living systems at risk of losing the ability to perform life-essential functions, such as when a plant becomes uprooted. Wind can result from weather phenomena or rapid movement through the air, as when flying. Wind is typically not a constant or predictable force, so living systems must be able to function both with and without its presence by adjusting to its direction and speed. A good example is how plants’ leaves and stems are flexible so that they can align with the wind, rather than being battered by it.

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Conifers and Others (Pines, Spruce, Gingko)

Clade Gymnosperms (“naked seeds“): Conifers, cycads, Gingko, gnetophytes

There are approximately 1,000 known species of Gymnosperms. These include well known needle-bearing plants like pines, firs, and spruce, as well as some with broad leaves like the Gingko and the gnetophytes. Instead of flowers, gymnosperms produce unenclosed (“naked”)seeds exposed on the surface of cone scales. Economically, conifers make up 45 percent of the world’s lumber production. The first gymnosperms evolved over 390 million years ago in the Paleozoic Era and dominated landscapes for a quarter of a billion years before the evolution and diversification of flowering plants.

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The trunks of pine trees withstands wind and snow via spiral growth.

Some trees, including the Pondersa pine, Scots pine, and Norway spruce, exhibit a spiral growth pattern in their trunks, branches, and stems. Some scientists suggest that because spiral-grained materials bend more than straight-grained materials, this spiral composition may help protect trees that grow in areas of high wind from breaking. A tree’s ability to bend and twist in strong winds may reduce drag forces on its limbs and also allow additional weight (such as that from snow) to slide off its branches when they twist in the wind.

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.

Blue arrows show deflection of wind as a result of spiral structure. Green arrows represent nutrients being distributed through the spiral structure to all aspects of the tree.

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Helical Wound Fibres Increase Toughness

Plants

Cellulose fibers in plant stems increase toughness by winding around tubes at an angle

Last Updated July 26, 2017

References

“…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)

Book

How Life Learned to Live: Adaptation in Nature

01/01/1983 | Helmut Tributsch

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Reference

“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)

Journal article

Function of spiral grain in trees

Trees | 31/08/2004 | Hans Kubler

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