Fall Foliage and the Chemistry of Color

 

Fall Foliage and the Chemistry of Color

Written by Kristine Manganelli (Somerset County 4-H Coordinator)

fall new jersey leaves color changing autumn trees nature outside outdoors kids activities

It’s happening! Right on cue, the autumn season has coaxed the Oak and Sycamore trees in my backyard into revealing brilliant shades of yellow and orange. This stunning show put on by nature every year is actually caused by a complex chemical process happening within the leaves themselves.

Here in New Jersey we have many deciduous trees—trees that shed their leaves each year in the fall. In the summer, leaves play an important role for deciduous trees in capturing the sunlight used to produce sugars in a process called photosynthesis. These sugars sustain the tree and help it grow.

Photosynthesis also pulls water into the tree which evaporates off the surface of the leaves. If the leaves did not fall off in autumn, the tree would continue to lose water when it needs to conserve during the winter. These leaf processes require energy from the tree, so shedding them allows the tree to also conserve energy for the season.

Chlorophyll is the green pigment present in all green plants, that is responsible for absorption of light during photosynthesis. Chlorophyll production requires light and warmth, so as the seasons shift to shorter, colder days, the chlorophyll in the leaves will decline. As we settle into the autumn season, the leaves are triggered to begin their yearly costume-change.

Since the chlorophyll breaks down more rapidly than other color pigments, the hidden orange, yellow, and red in the leaf are revealed. These pigments are always present, but only become visible as the chlorophyll begins to fade. The yellow-orange pigments we see are called Carotenoids, which also give carrots their orange color. Anthocyanins are red pigments found in grapes and apples, are present in the leaves of some tree species.

Maple Leaves in Autumn

Maple Leaves in Autumn

The quality of the color display in any given year is influenced by light and temperature. Cool, dry weather hastens the breakdown of chlorophyll causing the green pigment to fade. Sunny days help to produce the best color as it heightens sugar production in the plant as well as the formation of anthocyanins. Less favorable conditions like warm, wet weather delay the breakdown of chlorophyll and development of anthocyanins, leading to a less impressive color release.

Thus, the most intense autumn colors result when conditions are dry, days are sunny, and nights are cool but not freezing. The fluctuation of these factors is reflected in the chemical balance of the leaf, and in turn, in the vibrancy of its fall hue. Overcast, rainy, or freezing weather will shorten the length of peak rainbow foliage.

Eventually the vibrant shades of yellow, orange, and red will become brown, as the carotenoids and anthocyanins also begin to break down. This signals that tannins or brown pigments, have been released, starting the decomposition process.

As autumn sets in, a layer of cells is produced at the leaf stem forming a barrier called the abscission layer. This interrupts the renewal of chlorophyll and eventually causes the leaf to break away from the branch and fall to the ground. The abscission layer is like a scar that protects the branch when it is exposed after the leaf falls.

As all good things must come to an end, the colorful display is only temporary. Get outside and enjoy the moderate temperatures over the next few weeks, because the cycle of seasons will inevitably continue to winter, bringing with it bare trees and frigid weather. Soak up nature’s autumn spectacular, but know that it is part of a process that doesn’t last forever. It is a reminder that nothing is permanent, and that we should live in, and enjoy the present moment.

Get Outside

Go on a leaf hunt in your backyard! Collect as many different types as you can find! Use this guide from Our Family Code to identify the species of trees in your yard using clues from the leaf.

Sources:

 
Somerset County 4-H