For the past few weeks our neighbors have been raking and blowing fallen leaves into the streets to be hauled away to someone else’s compost heap. Soon all out trees will be bare, and most our leaves will be gone — only memories of a leafy summer will remain.
Or so I thought. Until I saw this:
Some leaves remained as ghostly stains on the sidewalks of south Oak Park! I found the first leaf prints after a week of wet weather had given way to the first dry day. Perhaps water-soaked leaves had been plastered to the sidewalk for days, leaching biochemical stains into the sidewalk cement.
The best individual prints were along this stretch of sidewalk:
The sidewalk here was pretty new, smooth and fairly flat, and the trees were small and evenly spaced. When leaves were scrunched instead of flat, or when sidewalk blocks were tilted, the prints were less than perfect:
When trees above were large or closely spaced, the prints were crowded together and often overlapped:
That must be why concrete street gutters are stained brown this time of year:
The first prints I saw were maple leaves — I wondered if other leaves could make prints, too. Searching the neighborhood sidewalks, I found some oak leaf prints, but they were on a older stretch of sidewalk, so weren’t as well defined:
Then I found some clearer oak prints on a newer sidewalk — but they were black instead of brown:
I looked closely and saw that these prints were made of dark dirt trapped in tiny rough spots on the sidewalk. They were dust-prints, not stains, because I could brush the prints away. I noticed that dust-prints had only formed in a sheltered spot, by a recessed door:
So, here’s my guess about how these prints formed: I think a layer of dust accumulated in the sheltered spot beside this little-used door. Then oak leaves blew onto the dusty sidewalk. The previous week’s rains had first plastered the leaves to the sidewalk — protecting the dust below — and then washed away the dust between the leaves. As the weather cleared, the oak leaves dried and blew to one side, exposing the leaf-shaped patches of dusty concrete below.
Now, here’s a question: If humans provide the concrete canvas, but nature does the rest, are these leaf prints art? I think not. But an artist inspired by these prints could make art using nature’s techniques. All that’s needed for stain-prints would be a stretch of newer sidewalk, leaves, water, and time — at least several days, I’d guess. To make the dust prints, you’d need new sidewalk, dust, leaves, and water. If I’m right about how these prints formed, you could make them in a few hours.
And if you try to do the art, you will also be testing my ideas about how the leaf prints formed. If my hypotheses prove wrong, then your art will fail, too. Hypothesis testing is science — so you’d be doing art and science at the same time!
Go here to read about the biochemistry of leaf stains. The stains may be made by tannins, or perhaps by pigments called anthocyanins.
Go here to contribute to a debate on “Is there a name for the stains left on sidewalks by fallen leaves?” Here are some of my favorite contributions from that debate (beyond “leaf stains”):
- Ghost leaves or tannin shadows (steef’s contributions)
- Leaftovers (krippledkonscious’s idea)
- Foliagraph (contributed by Terminal Verbosity)
Note added Friday, November 13, 2009: On this morning’s walk I found examples of a third type of leaf print on a concrete sidewalk. Here’s a photo of imprints made when leaves fell onto a concrete sidewalk right after it had been poured — when the cement that would eventually bind it all together was still soft and wet:
On a 20 foot stretch of sidewalk there were at least 50 prints of two types of leaves (plus a trail of squirrel footprints — more about that in another blog post). In addition to the Elm leaves, there were also a dozen prints that looked like a type of Basswood or Linden:
Although it’s hard to tell from these photos, the leaf prints were a couple of millimeters deep — that’s why I called them imprints. Because many of the prints were so perfect, I imagined that the leaves must have stayed in the concrete until after the cement had set, perhaps rotting in place. However, as shown in the photo above, some prints were not perfect — the leaves were folded or had slipped to one side after they had fallen into the soft cement.
So, I’m wondering if we can tell anything more from these imprints. Because there are so many leaf prints, does that mean the sidewalks were poured during autumn, when leaves were falling? Did strong winds blow the leaves onto the concrete and then fold or slide some once they were embedded in cement? Perhaps the evidence can’t rule our other possibilities, but it’s interesting to speculate.
By the way, other folks have posted photos of similar leaf imprints on the web. Some folks call them “sidewalk fossils,” and teachers sometimes use them to get students thinking about how fossils form:
If you’d rather make your leaf prints in a more portable form, here are some web pages to help get you started: