 Autumn, crisp mornings, mild afternoons, and beautiful fall colors. This is one of my favorite times of the year. Have you ever wondered what causes the leaves to change color in the first place? Most folks know that leaves are green for most of the year because of a pigment called chlorophyll. Chlorophyll converts water and carbon dioxide into sugars that the tree uses for energy. Leaves also contain pigments called keratines, which have a yellow or orange color. These are the same pigments found in kerats. As the days get shorter in the fall, the tree stops creating new chlorophyll, and the existing chlorophyll breaks down. The keratines break down more slowly than the chlorophyll, so as the green fades from the leaf, the yellow color of the keratin emerges, such as in our native aspens in cottonwoods. What about the reds we see in some trees, such as in these choke cherry trees? Well, as the tree prepares for winter, it starts sealing off the leaves. This causes sugars to become trapped in the leaves instead of traveling into the trunk. These sugars react with proteins inside the leaves and create brilliant shades of red. Take some time to get out and see the beautiful fall colors of Wyoming. From the University of Wyoming Cooperative Extension Service, I'm Zola Ryan.