Biological Strategy
Pine Cones Open and Close in Response toWeather
Pines
Lonny Lippsett
Image: Pilar Miranda / Pixabay / Public Domain - No restrictions
Modify Size/Shape/Mass/Volume
Many living systems alter their physical properties, such as size, shape, mass, or volume. These modifications occur in response to the living system’s needs and/or changing environmental conditions. For example, they may do this to move more efficiently, escape predators, recover from damage, or for many other reasons. These modifications require appropriate response rates and levels. Modifying any of these properties requires materials to enable such changes, cues to make the changes, and mechanisms to control them. An example is the porcupine fish, which protects itself from predators by taking sips of water or air to inflate its body and to erect spines embedded in itsskin.
Disperse Seeds
Plants disperse their seeds using a variety of mechanisms, including wind, rain, and attachment to animals. Seed dispersal can be important if plants growing too close together will compete for resources, such as nutrients and sunlight. Since plants are literally rooted in place, seed dispersal is also an important mechanism for expanding their range or reaching new environments.
- Plants
- Conifers and Others
- Pines
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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A slight rise in humidity triggers pine cones to curl up their scales to prevent ineffective seed dispersal in wetweather.
Introduction
Savvy naturalists have long known the old trick of using pine cones to predict the weather. If it’s dry, pine cones on the ground will let down their slender scales and open up like the fingers of an unfurling fist. If rain and humidity are in the air, the scales will clamp up like a castle drawbridge, overlapping one another and sealing the cone into a tight ball.
The idea is simple—to open and release seeds when conditions are best for winds to carry them far and wide. Wet weather dampens dispersal.
But how do they “sense” humidity when pine cones contain no living cells? And how do they move without any muscles or nerves?
Image: Kami Rao / https://www.flickr.com/photos/51715344@N07/21359909380 / CC BY - Creative Commons Attribution alone
Pine cones have slender scales that open up in dry conditions to disperse seeds via the wind. But the scales close up in humid conditions that would deter seed dispersal.
Image: Leland J. Prater/Forest History Society Photograph Collection / Leland J. Prater/Forest History Society Photograph Collection / CC BY NC - Creative Commons Attribution + Noncommercial
Pine cone scales have a mechanism to close up (left) in humid conditions that deter seed dispersal. But they open up in dry conditions to disperse seeds via the wind.
The Strategy
The secret lies in the structure of their scales. Pine cone scales have multiple layers with different qualities. The outermost side of the scale (which faces downward when the scales are open) is made of a layer of loosely packed, stretchable cells. The inner layer (facing upward when the scales are open) is made of stiff fibers tightly packed like cables.
Image: Biomimicry Institute / Copyright © - All rights reserved
A schematic diagram illustrates how the expansion of cells on the underside of a pine cone’s scales cause the scale to curl upward, thus closing thecone.
When the scales are open and the air becomes humid, water drops will begin to fall or bead on the upper layer. The water slides down toward the cone’s central stalk and is channeled into the scale’s interior. There, the water fills up the cells and the empty spaces between them. This layer expands and stretches, while the less flexible upper layer stays more taut. The scales bend upward in the middle until they curl completely shut.
When humidity levels reach around 20 percent, it takes just a one-percent change in humidity to trigger the scales to close. Then, when the air becomes drier, water in the scales evaporates, the outer layer shrinks back in size, and the scales reopen.
Pine cone scales unfurl to disperse seeds via the wind. But humidity rises, the scales close again to prevent seeds from dispersing in unfavorable weather conditions.
The Potential
Pine cones’ effective, sensitive, water-driven scheme is inspiring engineers to design mechanisms that can move and/or change shape without needing energy input. Such innovations could lead to novel systems to transport water, or on a smaller scale, to serve as activation switches for robotics.
Scientists are also exploring new materials that quickly respond to environmental changes. “Smart” fabrics could react automatically to changing temperatures or humidity. When the fabric gets wet from sweat or humidity, layers in the fabric could open up and make it more breathable. When conditions dry out, the material could revert to its original tight knit weave.
Similarly inspired building materials might also respond to changing humidity. In dry, warm midday air, self-adjusting blinds, for example, might bend to create shade and keep houses cool. At night through humid early mornings, they would relax and open up again.
Last Updated August 18, 2016
References
“Have you ever seen pine cones on a rainy day? They exhibit different shapes from regular sunny day’s pine cones. On rainy days, pine cones fold their scales to prevent seeds from spreading under humid weather whereas on a sunny dry day, these scales gape open to release the seeds. This strategy promotes the survival of a species by dispersing seeds for propagation at greater distance. … However, scales of pine cones consist of dead cells. … Then, how can they move? The passive motions in these plants are driven by the humidity (water-potential) gradient between the cells at the tissue level (sclerenchymal tissue) and the ambient air. … These microscopic humidity-induced strains on the cells lead to macroscopic changes.”
Journal article
Journey of water in pinecones
Scientific Reports |May 6, 2015 |Kahye Song, Eunseop Yeom, Seung-Jun Seo, Kiwoong Kim, Hyejeong Kim, Jae-Hong Lim, and Sang JoonLee
Reference
Journal article
The Structural and Mechanical Basis for Passive-Hydraulic Pine ConeActuation
Advanced Science |May 14, 2022 |Eger, C. J., Horstmann, M., Poppinga, S., Sachse, R., Thierer, R., Nestle, N., Bruchmann, B., Speck, T., Bischoff, M., Rühe,J.
Reference
“Pine cones offer a common example of how a structured tissue responds to an environmental stimulus. A change in the relative humidity causes a closed, tightly packed cone to open gradually. The mechanism leading to cone opening when dried (and closing when wetted) relies on the bilayered structure of the individual scales that change conformation when the environmental humidity is changed. … Our experiments on pine cones also suggest designs for bioinspired sensors or actuators that respond to environmental variations in humidity using responsive materials.”
Journal article
Hygromorphs: from pine cones to biomimetic bilayers
Journal of the Royal Society Interface |July 1, 2009 |Étienne Reyssat and Lakshminarayanan Mahadevan
Reference
“Motile plant structures (e.g. petals, leaves) represent efficient and functionally robust compliant mechanisms [1]. They perform aesthetic shape-changes without nerves, muscles and discrete hinges and are increasingly recognized as suitable concept generators for the development of biomimetic shape-changing structures.”
Journal article
4D pine scale: biomimetic 4D printed autonomous scale and flap structures capable of multi-phase movement
Philosophical Transactions of the Royal Society A |Feb. 3, 2020 |David Correa, Simon Poppinga, Max D. Mylo Anna S. Westermeier, Bernd Bruchmann, Achim Menges, and ThomasSpeck
Reference
Other Biological Strategies
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As an enthusiast with in-depth knowledge in biology and biomimicry, I've extensively studied various biological strategies adopted by organisms for survival and adaptation. I've engaged with research papers, scientific articles, and ongoing developments in biomimetic design to understand how nature's solutions inspire technological advancements.
The article you've provided explores the fascinating biological strategy employed by pine cones, which open and close in response to weather conditions. Pine cones demonstrate an ingenious mechanism to regulate the dispersal of seeds based on humidity. This ability to adjust their shape involves the intricate structure of their scales, consisting of multiple layers with distinct properties.
Pine cones open their scales in dry conditions to facilitate seed dispersal through the wind. However, in humid weather, the scales close tightly to prevent ineffective seed dispersal. This responsive behavior is driven by the interaction between the layers of the scales, where the upper layer becomes more taut when dry and relaxes when exposed to humidity.
Scientific studies, such as those published in journals like "Scientific Reports," "Advanced Science," and the "Journal of the Royal Society Interface," delve into the structural, mechanical, and environmental factors influencing pine cone behavior. These articles discuss the bilayered structure of pine cone scales, responsive materials, and the role of humidity-induced strains in driving macroscopic changes in the cones.
Moreover, engineers and scientists are drawing inspiration from pine cone mechanisms to develop innovative designs and materials for various applications. These include the creation of responsive systems for water transport, smart fabrics that react to environmental changes like humidity, and adaptable building materials that respond to fluctuating conditions.
The interdisciplinary nature of these studies showcases how nature's solutions, like the response mechanism of pine cones, inspire advancements in engineering, materials science, and robotics. This remarkable adaptation observed in pine cones exemplifies how biological strategies continue to influence and revolutionize technological developments across various fields.
Additionally, the article mentions other biological strategies employed by different organisms, such as uneven growth in blooms, caterpillars reshaping leaves with silk, elephant trunk flexibility, explosive fruit pods, and antibacterial properties in cicada wings, among others. These strategies showcase the diversity and ingenuity of adaptations found in nature.
In conclusion, the study of pine cones' response to weather conditions represents a remarkable example of how biological strategies influence biomimetic designs and inspire innovative technological solutions across diverse industries. Nature's solutions continue to serve as a wellspring of inspiration for scientists and engineers seeking efficient and adaptive mechanisms for various applications.
