The Pigments of Leaves
The colors of the fall leaves can bring an incredible beauty to the landscape. Each tree has its own color group, making the countryside look like a painting. We begin to notice that the shades and tones of the leaves start changing when the weather gets a bit cooler. Altering from their bright summer green and slowly turn into gold, orange, brown and reds.
To understand what makes the leaves change their colors or pigments, we need to know how leaves work. The leaf of a tree uses a process called ‘photosynthesis’ to survive. The process uses a chemical in the leaf called ‘chlorophyll’ to change the sunlight into the food that it needs. Chlorophyll in its natural state is green. In the summertime, the chlorophyll fills the leaf at such a density, that the only color that you see is the green of the chlorophyll.
What you might be surprised to know is that even though the only leaf color that we see is the green color, there are actually other orange and yellow colors that are contained in the leaf. The chlorophyll green overtakes these colors so that the only way someone might see them is under a microscope.
As the weather begins to cool and the sunlight dims, the amount of chlorophyll in the leaves begins to be reduced. At the same time, there is a natural process in the trees that start producing red colors that are sent out to the leaves. As the chlorophyll disappears, the yellows and oranges that were always there become easier to see.
When the air starts to become drier the tree will also begin producing more sap in a concentrated fashion. The sap concentration is what gives the leaves the red colors. Leaves that start turning brown are actually the result of the tannin that the tree produces. Tannin is a waste product of the tree and the leaves absorb it.
You may have noticed that not all fall tree colors are as bright or the same each year. This is due to the amount of sun that may have been taken in during the season. Some years, the leaves begin to turn to their fall colors more quickly, while others are slower to change and may be more brilliant. Long summer days that are dry and sunny, combined with cool nights produce the most colorful leaves.
Different trees also seem to have more of one color in their leaves than others. The trees that make a high quantity of yellow leaves in the fall are White Ash, Basswood, Birch, Aspen, Witch Hazel and Hickory. The best trees with the reddish colored leaves are Red Oak, Sumac, Red Maple, Mountain Ash, Sumac, Sour Gum and Dogwood. Evergreen trees do not change color. Instead, their leaves are covered in a waxy thin coating that last for a few years.
There are also other plants that experience color changes due to the alteration of chlorophyll. Poison Ivy and Virginia Creeper have leaves that change to red and variegated colors and Wild Grape has purple vines and berries.
Can you locate the various tree types by the color of their fall leaves? An experiment might involve keeping track of the weather and as fall nears, observing the process of the changing of the leaf colors to gauge how quickly they will turn colors.