Leaf Prints: Nature’s Ghost Leaves
by Jan Dabrowski
Fall is the time that ghost leaves appear on campus and around town. You’ll see them best on the lighter concrete walks.
A ghost leaf is the print left behind after wet leaves lying on the walks for a day or two have been blown or swept away. In some cases, the ghosts are very sharp and show details as small as veins in the leaf.
Eric Ashford captures the essence of ghost leaves in his poem:
The fallen leaves
have left rusty impressions
upon the sidewalk.
Pressed russet prints
on the unyielding concrete
the flight of the season.
I try not to step
on these ghost images.
Believing that if I walk gently
through their painted dreams
Autumn will keep step with my life
and not overtake it.
~ Eric Ashford, 2006
Why ghost leaves appear is connected to why leaves change color in autumn.
Chlorophyll, the chemical responsible for photosynthesis – the source of energy and food for plants – drains from leaves with the prelude of winter weather.
The colors the leaves become are caused by pigments that have been in the leaves all along, but masked by the chlorophyll. In a real sense, the leaves don’t turn color, but finally reveal their real colors that have been hiding all summer long!
Fallen leaves, wet from typical October and November Portland rains, lose their pigments. The pigments and other chemicals from the wet leaves stain the ground beneath them. When a sunny day intervenes and dries the leaves, they blow away and their leaf prints remain as stains in the concrete. They stay until new rains wash them imprints away.
The chemicals that leave behind the grey-black image are tannins and anthocyanin.
Tannins give the tea-color to tea and are found in most plants. Tannins get into streams from decomposing plants and this can result in what is known as a blackwater river. Slow moving by nature, blackwater rivers can’t clean themselves and the tannin concentration, and the dark color builds.
Anthocyanin is one of several pigments found in leaves as well as in flowers and fruits. It comes from the Greek for flower (anthos) + blue (kyanos).
Catch the fleeting ghost leaves of autumn while the falling leaves are with us.
Jan Dabrowski is an associate professor at Marylhurst University, teaching science and interdisciplinary studies. Jan’s career in science began at the age of five with a visit to the Hayden Planetarium in New York City. He has maintained an avid interest in astronomy, physics and other sciences ever since.
Photo by Joanna Brichetto