Why do leaves lay on the ground the way they do?
by David Schwartzman
Observing nature is an interesting habit. Check out these two photos:
A: veins face up, convex up.
B: veins face down, concave up
If you observe a large number of fallen leaves on flat ground, which orientation do you predict is most common, A or B?
While I was jogging in Rock Creek Park this past autumn I happened to notice for the first time that orientation A was the most common, confirmed for beech, oaks, and sycamore.
I think they lie on flat ground convex-up because that is aerodynamically more stable. A gentle wind will turn leaves over until they reach this orientation.
This is my conclusion, but I cannot find a scientific study to confirm. Thank to my colleague Mike Rampino, Professor at NYU, we know of a similar situation: shells at the beach are mostly concave side down, which is the stable configuration. If the currents move the shells around randomly, when they get in the concave down orientation they stay that way. (Plotnick et al. (2013) The Orientation of Strophomenid Brachiopods on Soft Substrates. Journal of Paleontology, 87(5), 818–825.)
Please see if your own observations will confirm this, and let us know what your results are, here in the comments, or below via my email.
David Schwartzman, firstname.lastname@example.org.