Why do the leaves change color in the fall?

One reason why the autumn colors are so remarkable in the Great Smokey Mountains National Park is the amazing variety of trees. Over 100 species of trees live in the Smokey Mountains and a great majority of these are deciduous (trees that lose their leaves seasonally).

What causes the tree leaves to change colors? As summer ends and autumn comes, the days get shorter and shorter. This is how the trees "know" to get ready for winter. As summer ends, the green pigments in the leaves begin to deteriorate, giving other colors a chance to shine through. As the bright green fades away, we begin to see yellow and orange colors. Small amounts of these colors have been in the leaves all along. We just can't see them in the summer, because they are covered up by the green. Carotenoids, the pigment that makes carrots orange and leaves yellow, are exposed as the green pigment fades. Reds and purples come from anthocyanins, a pigment that is formed when the sugars in leaves break down in the bright autumn sunlight.

The best place in the world for viewing fall colors is probably the Eastern United States, home of the Great Smokey Mountains National Park. This is because of the climate, and the wide variety of deciduous trees. The brightest colors are seen when the late summer is dry, the days of autumn are bright and sunny, and the autumn nights are cool (low 40’s). Then the trees make a lot of anthocyanin pigments. An autumn with cloudy days and warm nights produces drab colors, and an early autumn frost can bring a quick end to the beautiful fall foliage.