“Plants are amazing!” This is something I hear a lot from non-botanists. Of course, I know plants are awesome, but every time I turn around, I learn something new and exciting. This semester was no exception. Tasked with a project in my Biomimetic Design class, led by Dr. Petra Gruber, I walked into the meadow to find inspiration– literally.
On a very wet, cold, rainy day in October, I walked to a meadow within our field station property (Bath Nature Preserve, Bath Twp., Akron, Ohio) and found a section to investigate. Indian grass (Sorghastrum nutans) towering over my head, I decided to stop at 20 steps and set up a 1m x 1m plot to sample. October in a meadow doesn’t give you very much to identify, but goldenrod (Solidago spp.) and Indian grass (S. nutans) were plentiful among a few baby asters, Galium spp. (aka ‘Cleavers’ or ‘Bedstraw’), wild strawberry (Fragaria virginiana),clumps of unidentifiable grass and moss. I measured heights of stems and area covered, took the percent coverage to determine how much each species covered the plot,and took several picture views for record. After returning to campus, I created a hand-drawn schematic of the plot.
A few weeks later, I returned to the same plot. Apparently my methods of counting and direction are spot-on because my last step landed on a pen I had dropped on that rainy day a few weeks earlier! If you’ve ever done field work, you understand how amazing it is that I found a PEN in the middle of a meadow over 2 meters high! This time I was there to measure the ability of the meadow to hold a load. I admit, I didn’t think the stems would hold up… being so late in the year and being dried out. As usual, though, plants are amazing and surprised me yet again!
I decided to test the load by creating a 1m x 1m foam board that was sturdy, yet lightweight. I placed the board directly over the plot, placing flags on each corner. The flags allowed for a visual cue to observe movement of bot
h plants and the board, as well as giving a reference point at which to measure the height of the board after each addition of weight. After the foam board was placed on top of the plants, I measured the height at each corner (flag) for the “initial” height. I added one heavy book and measured the height at each corner. Subsequently, I added increasing weight and measured the heights. At 3 books (6.7kg), the system (the meadow plot) could no longer hold the weight. Because this was the same plants were used over the entire experiment, I believe more weight can be held by the plants in true form.
So how does this happen? Plants are amazing. In the meadow, plants grow up to 10 feet below ground (roots) and above ground. You can imagine how secure this makes these cantilever beams! Here, the Indian grass and Goldenrod grew 1.5m to 2.5m above ground. The stems reached diameters of 2-5mm. You may wonder how the stems did not break when the weight was added. Galileo was the first to record these observations, noting that bending is resisted in the outer layers, not the inner stem as some might think. Several studies have investigated this design, including F.O. Bower (1930) who compared plant stems to concrete, saying, “Ordinary herbaceous plants are constructed on the same principle. The sclerotic strands correspond to the metal straps, the surroundin
g parenchyma with its turgescent cells corresponds mechanically to the concrete.” Equisetum (Horsetail) is another champion plant for many reasons, but here, in this context, it’s a biomechanic superstar. “The hollow stem of Equisetum giganteum owes its mechanical stability to an outer ring of strengthening tissue, which provides stiffness and strength in the longitudinal direction, but also to an inner lining of turgid parenchyma, which lends resistance to local buckling. With a height >2.5 m isolated stems are mechanically unstable. However, in dense stands individual stems support each other by interlacing with their side branches, the typical growth habit of semi-self-supporters.” (Spatz, Kohler, Speck 1998). Again, plants are amazing.
After doing some mathematical calculations (very much estimated
in this case because of the imprecise nature of this ‘experiment’), it is expected that a single Goldenrod stem can support >118% of its biomass! Now, we’re not talking about the strength of steel or lead, but we can see that plants offer us new possibilities when we are designing or constructing new things! Imagine a support feature that is hollow inside and allows for storage in the “stem” as well has having the strength to support weight. Think on a smaller scale: imagine a space in which a stiff, lightweight outer covering is needed to secure something. Imagine the many possibilities that plants offer us to grow using Life’s Principles.
Thank you for continuing to follow us, the biomimicry fellows, as we continue to probe the depths of nature’s solution manual in search of sustainability. I find it a little ironic that I had the privilege to kick off the school year and now I will be closing out the first semester for the new biomimicry fellows. Over the last fifteen weeks we have been endeavoring to discover more about this thing we call biomimicry. I’d like to take a second to share a few of my thoughts that have been shaped this semester. Continue reading