This week has served as nice reminder that fall is here! The cool crisp air might have you ready to go check out the foliage, but it’s still a little early for the best colors. Here in the Tennessee Valley the foliage starts to change around mid-October, but it doesn’t peak until early November.
When the leaves start changing is primarily controlled by the amount of daylight we see. Since we lose daylight hours at the same rate every autumn, we can use this to predict when our foliage will peak. While the timing is consistent year-to-year, how vibrant and intense the colors are can vary. That depends on two factors: the pigments within the leaves and the weather.
During the spring and summer plants are producing chlorophyll. This is the green pigmented compound that allows plants to absorb sunlight. Then the sunlight, plus carbon dioxide, is turned into sugars and energy for the plant. Other compounds and pigments are still present in the leaves, it’s just that the amount of chlorophyll present overwhelms the other compounds, which produces the predominantly green hue.
In the fall, the decreasing amount of daylight as well as changing solar angle signal to the trees and plants that winter is coming. As a result, the trees and plants gradually halt production of chlorophyll as well as divert water resources from the leaves to the trunk or branches. As the chlorophyll fades away, other compounds present in the leaves produce the vibrant colors that we see every autumn.
As the leaves become sufficiently dry, they are no longer able to remain attached to the tree or plant, and they fall to the ground during the season.
Different compounds within leaves produce different fall colors
Depending on the tree or plant, various compounds will produce the varying fall hues that we enjoy every autumn. These compounds include carotenoids, flavonoids, and anthocyanins. An in depth analysis of these compounds are available on the chemistry infographic site Compound Interest.
- Carotenoids and flavonoids produce yellows and oranges, and they break down at a slower rate than chlorophyll. According to Compound Interest, notable carotenoids seen within the leaves include beta-carotene (the same compound that makes carrots orange); lutein (the same yellow compound found in egg yolks); and lycopene (the same compound that makes tomatoes red).
- Anthocyanins are a type of flavonoids that aren’t usually present in the leaf in the spring/summer. Instead, they are generated in the fall as the sugars in the leaves concentrate (due to the decreasing amount of moisture as fall creeps into winter). Anthocyanins produce the vivid red, purple and magenta shades.
Sunny days in the fall can aid in the production of sugars, while chilly nights will help break down chlorophyll more effectively. So, it’s the brightest and crispest fall days that can bring about the best fall views!