Leaf Shadows: Stained Concrete
Here in Oregon, we get a lot of rain and fall leaves all at once. Often they leave sidewalk stains that are like ghosts of their past selves. But why?
Sometimes they stay there for a long time…
leaf stains photo by John Kannenburg via Flickr
Don’t feel bad that you don’t know the answer because several professors of plant ecology were also unsure.
The best answer I have found is tannic acid. The cause of this is the result of the chemicals found in leaves. Tannins, which were used in iron gall ink and for tanning leather, leave their mark on the sidewalk. Tannins also give tea its color.
Tannic acid is also soluble in water, which explains the stains. Also supporting that theory, Dr. David Starlett of Southeast Missouri State University, observed that “On a hill, the stain smears to the downhill side, with streaks often maintaining leaf width.”
He also mentions that he’s a plant ecologist not a plant physiologist, and is still unsure of the exact cause.
Sometimes its nice to know that not everyone knows the answers. Most experts cite tannic and humic acid as the cause but I have yet to see something definitive explaining the cause, process and results. Maybe I should ask a phytochemist?
Kallen is currently pursuing a Bachelor's degree in Biology and Journalism at the University of Oregon and, of course, writing a blog.
Samper said,
November 10, 2008 @ 3:48 pm
Hum…interesting. Does the tannic acid have some sort of reaction with the concrete?
Perrin said,
November 28, 2008 @ 4:03 pm
Ahhhh…..
Post more; it’s always interesting.
Sarita said,
December 29, 2008 @ 5:32 pm
I’d been curious about why leaves do that. Guess I’ll remain curious as to its exact cause for some time yet.
On one hand it’s annoying to be in the dark about things. On the other hand, what would there be left to do if we had all the answers?
Sonja said,
December 30, 2008 @ 8:13 pm
I have always been facinated by the beauty of leaf stanes on the sidewalk. I have never really given any thought as to how they were created. I just asumed the natural die or color in the leaves just leached out from the moisture. However they are created they are truly fun to see. And fun to photograph. Natures stencle.
I do love your inquisitive mind. keep it up.
Bruce Daub said,
August 13, 2009 @ 9:47 am
How do I get the leaf stains out of my 1 year old concrete patio so I can seal it?
Natural Leaf Prints on a Concrete Canvas « Neighborhood Nature said,
November 9, 2009 @ 6:05 pm
[...] Here’s someone else who blogged about this topic: Leaf Shadows: Stained Concrete. [...]