Fall Colors, and How They Occur - Is Jack Frost really responsible?
By Jim Eagleman
We’ve all heard versions of the Jack Frost story and his coloring of fall leaves. As it gets cooler with each autumn day, we can almost imagine his nightly visits with pallet and paintbrushes in hand. But, scientists tell us that while it has something to do with warm days and nightly frost, there’s much more to it. Actually, to understand how fall colors appear, let’s look back to the tree in mid-summer.
As the leaves twisted in the summer breezes, and with bright sunshine overhead, the tree leaves produced a substance called chlorophyll. This green color pigment in the tiny cells of leaves gave us a shady ceiling all summer of shimmering layers, shapes and textures in the forest. Think of the green chlorophyll as a mask, like a Halloween mask. Hidden behind the green color of the chlorophyll all summer were other colors that were masked, or hidden from view.
As fall approaches, temperatures cool and daylight hours shorten, production of new chlorophyll begins breaking down and slowly disappears as fluids are withdrawn from the leaves. The green color in the cells began to break down and the color show we are used to seeing really begins.
The red color like a similar one we see in the Cardinal or red apple, and also in blueberries, is called anthocyanin.
The yellows and oranges of Sassafras and the maples, and also known to occur in bananas and pumpkins, are due to the pigment, carotene.
In oaks and hickory leaves, the chlorophyll simply fades from tans to brown, produced by tannins that we find in teas and coffees.
Scientists claim that it is sunny, warm fall days, followed by crisp, cool nights that “trap” sugars and other chemicals, particularly in the maple trees, as they are drawn from the leaves. These extremes in daytime and nighttime temperatures are what produce the best fall color. From the leaves, fluids are slowly drawn through twigs and down into the trunk and finally into the roots. In the spring, when we say the “sap is rising,” just the opposite happens. The fluids return and the production of chlorophyll begins, anew.
Certain trees have distinctive colors during the fall: red maple a brilliant red; green ash and aspen turn golden yellow; oak and hickory become a reddish brown color; white ash a deep purple; and sumac a scarlet red. Even the tamarack, an evergreen tree, turns a beautiful deep golden yellow and loses its needles in the fall.
There is nothing quite like fall in Indiana, when you walk through the autumn leaves scattered on the ground, seeing the kaleidoscope of colors all around, listening to the song of the trees as the gentle breeze of autumn rustles through their leaves. Enjoy our Hoosier autumn days. They don’t last long.
A great place to see the great color show is to visit a DNR property and hike on some of their trails. Watch your favorite tree as its colors begin to appear this fall; you won’t be disappointed.