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Why do leaves change color in autumn?

For many people, autumn is a favorite season, not just for the pumpkin spice lattes, but because of the vibrant shift of green leaves to an incredible array of warm colors. What causes the leaves to change color?

Dr. Mike Kuhns, a Professor and Extension Forestry Specialist, describes how the trees prepare for this change: “At the end of the growing season, the plants sense that it's time to start shutting down for the winter.”

The plants prepare for dormancy by moving the amino acids and sugars produced by chlorophyll from the leaves to woody tissues. For the long term winter these sugars are stored as starch.

Dr Kuhns explains: “The leaves for most plants have been emptied of sugar and starch. That makes the fall color change as well but when the chlorophyll breaks down, you no longer have the green available to give it a green color. And usually, what's left is what shows as the fall color. That orange or yellow pigment is called carotenoid pigment. And chances are it was there when the chlorophyll was there with the chlorophyll masks the presence of other colors.”

The next time you take a look at the Utah canyons keep an eye out for particular colors.

“The Bigtooth Maple will be the most likely to have yellow to red and the pink comes somewhere in between, but it would be like shocking pink. The quaking Aspen, yellow is their main.”

To learn more about upcoming forestry events and to access informative tree resources  written and organized by Dr. Kuhns for tree identification, visit 

For more information about forestry visit:

Colleen Meidt is a Science Reporter at UPR as well as a PhD student at Utah State University. She studies native bees in the Mojave Desert and is particularly interested studying the conservation status of the Mohave Poppy Bee. In her free time, Colleen enjoys photography and rock climbing in the canyons.