Why Leaves Change Color

Learn more about Fall leaves.

       Each autumn the leaves of many of our trees and shrubs change from green to bright colors, before they turn brown and drop to the ground. Beautiful effects are created in our parks, our forest preserves, and along the tree-lined roads as the leaves red, purple, yellow, green, and brown‚ blend into a harmony of color. On cloudy days the mass of yellow lightens the countryside and gives the appearance of reflected sunshine.
       The different shades of color are often so intense or so delicate that even the most casual observer will notice them and wonder why the change occurred. Probably no one knows exactly how this change in color happens. Many believe that the frost causes it, others do not. At any rate the change in coloring usually comes in the autumn about the time of the first frost. It is then that the deciduous trees (those which lose their leaves) begin to prepare for winter. The leaves have finished their summer's work of manufacturing food for the tree and as their activity slows down, the green tint begins to disappear. With the fading of the green, the yellow and orange appear. Probably these hues have been present in the leaves all the time but have been covered by the green color. As the leaves finish their work, the circulation of water and food in the entire tree slows up. Often some of the food, which naturally would be carried into the trunk for storage, accumulates in the leaves, where it is trapped. At about this time the cool weather comes along, and the complicated chemical reactions which start within the leaves produce the red or purplish tints.
       Certain kinds of trees become more brilliant than others and even among trees of the same kind there is a variation in color. For instance, the sugar maples turn yellow, red, and orange. The scarlet, pin, and red oaks become red, and the white oak turns almost purple. Usually the red maples, dogwoods, sweet gums, wild plums, and sumacs turn various shades of red or scarlet, while the silver maples, locust trees, poplars, tulip trees, birches, and witch-hazels become different shades of yellow.
       Other trees, like the bur oak and the hickories, sycamores, horse chestnuts, and wafer ashes, change only to dull brown.
       Only deciduous trees change into autumn colors, the evergreens do not. Some regions such as Florida, sections of mountainous evergreen forests, and the tropics do not have the climatic conditions and the varieties of trees that produce bright autumn coloring. In North America, the regions which appear exceedingly beautiful in the fall are the eastern states stretching from Canada southward and from the eastern coast to the great plains, and certain regions like the Missouri Ozarks, where deciduous trees cover the mountains.
       Many leaves show various tints in the spring when they first open. The green color appears only after the leaf is exposed to the light. When the buds first open the small leaves are pale yellow, pink, or almost colorless, but as they continue to unfold and as the sun shines more directly on them the green color begins to appear and soon covers up any other hue which might be present. Young oak leaves are red in the spring for a short time, and shagbark hickory leaves are wrapped in delicate yellow and pink bud-scales. As the bud unfolds, the scales drop back and the yellow-green leaves uncurl in the light and soon become deep green in color.
       These leaves usually remain green all through the summer while they are manufacturing food for the trees. However, if the tree is injured or does not receive enough water and food, the leaves will fade, wither, and drop to the ground, regardless of the time of year. Leaves change color as they die. However, most leaves die only after their work has been finished and that is in the fall of the year in temperate climates. And so the autumn, with its warm days and cool nights, is the time to see the leaves attired in brilliant color. Wood

About Fall leaves from SciShowKids