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  • Writer's pictureMason Edwards!

Chattanooga’s Autumn Scenery Raises Questions: Why Do Leaves Change Colors in the Fall?

Updated: Dec 23, 2023

By Mason Edwards, Staff Writer for the University Echo

Out of the thousands of things to like or dislike about Chattanooga, there is one element everyone can love: how the shades of crimson red, pumpkin orange, and corn-like yellow scatter on the ground and color the mountains above.

From far away, the hills look as if they were painted on with an autumn palette. The past two weeks, Vine Street could have been renamed Leaf Street. 

UTC staff endeavored to control the leaves, blowing them into heaps along the sidewalks —perfect for leaping into. Some students even took a chance to relieve better days and splashed in the piles.

Plumes of multi-colored leaves cascaded through the air, picked up by supple gusts of tame winds, and were carried away. It is the kind of freedom and energy that everyone can enjoy, and it especially resonated with students at UTC. 

Moreover, watching the trees shed their leaves symbolized the end of the fall semester. One where students, staff and faculty alike enjoyed more freedom than last year’s end.

Maybe, as one watches the branches freely sway and the leaves catch the breeze, they grow thankful for the year that did bloom.

This leads one to ask — in the spirit of thankfulness — what do we have to thank for our lovely fall scenery? In short, leaf abscission, the technical term, is more than meets-the-eye.

It is common knowledge that not all leaves change colors — like the cone-shedding coniferous trees. Mocs certainly count themselves lucky to be surrounded by deciduous trees.

A botanist will not have to explain chlorophyll, the chemical responsible for the green hue of leaves, during spring and summer; however, it might surprise one to know that leaves have more than one pigment. 

As the summer sun dwindles and the chloroplast loses sunlight required for photosynthesis, the leaves stop producing chlorophyll. It is a chemical change, brought in part to the lowered temperature. The green gradually fades, and other colors come to light. 

There is always a mixture of four colors, according to the Harvard Forest. Anthocyanins make a plant red, Carotenoids make a plant orange, and Xanthophylls make a plant yellow.

Depending on the tree, according to the State University of New York Syracuse College of Environmental Science and Forestry, “Some mixtures give rise to the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange.”

That explains the colors, but not why the leaves drop in the first place. 

It is reminiscent of “Turkey Drop” where freshmen couples break up before Thanksgiving. Trees shed their leaves as a form of self-protection through the ensuing winter.

Melissa Petruzzello — a Britanicca writer who aquired her M.S. in Plant Biology and Conservation from Northwestern University — said “since water expands when frozen, the tender leaf cells would rupture during the winter, making them useless for photosynthesis.”

Instead of the leaves simply falling, the process is controlled, with the tree selectively cutting ties from the leaves. Like blood clotting, the trees close off the vessels between the twig and branch. 

She adds that with the leaves on the ground, their nutrients can be reabsorbed for spring when the tree blooms again. 

One should not miss the significance of the trees’ self-sacrifice, like squirrels tucking away acorns for the winter, since it is common knowledge that seasons impact emotion. The glamorous colors of autumn double as warning signs for the harsher season of winter, and while the trees lose pieces of themselves, they will grow stronger in the spring.  

As the days get shorter and colder and a new semester brings fresh worries, remember that the empty trees are merely hibernating, ready to awaken next spring stronger than ever.  

Perhaps, with a better understanding of the science—students, staff, and faculty will not simply look at the living, stunning tapestry that is Chattanooga in the fall, but admire the season for all its virtues: aesthetically, functionally, and symbolically. 

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