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How a Leaf Changes Color in Fall

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Introduction to Fall Leaf Color Change
Autumn leaf cross section

Autumn Leaf Cross Section

Illustration Courtesy of USFS
The annual change in tree leaf color actually starts just after the longest day and first day of summer, June 21 in the Northern Hemisphere. That is the day the earth tilts to the point where the sun returns on a path back toward the Southern Hemisphere. You will not see the change yet but internal changes increase the tempo toward brilliant fall leaf colors.

Chemical changes that turn leaves from pale green in spring to dark green in summer to yellows and reds in fall are quite complex. The green pigment in chlorophyll, and stored in plastids, diminishes and is replaced by a pigment color without chlorophyll. The exact color is determined by each tree species.

There are three major components for pigment change in leaves. Plastids (1) are minute leaf structures that carry green chlorophyll and color the summer forest. Carotenoids (2), stored in plastids, and anthocyanins (3) in leaf sap are the leaf paints (pigments) that color the forest of autumn.

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