Why autumn leaves change color and fall
Understanding the science behind the transformation of leaves through a series of photographs.
Monday, November 15, 2010 - 13:54
Photo: Heather Altherr
One of the most notable elements of fall is the foliage of trees. You see it all over: the foliage turning hues of reds, oranges and yellows, and the countless number of leaves that fall and blanket the ground.
Have you ever wondered why leaves change colors and fall? The answer can be found in three different chemicals involved in producing leaf color and a leaf's cellular structure.
The green color of leaves is produced by chlorophyll. During the spring and summer, chlorophyll is constantly being produced. In the fall, as the nights grow longer, less chlorophyll is produced, unmasking yellows.
Yellows are always present in the leaves, but they become unmasked when the production of chlorophyll ceases. These yellow pigments are carotenoids and can be found within the leaves of birch, beech, aspen, poplar and black maple trees. Carotenoids protect the leaves from the byproducts of photosynthesis.
Anthocyanins, which produce the reds and oranges, found on oak, hickories, dogwood and sugar maple are produced when the tree becomes dormant. Red pigments protect leaves from the sun, enabling the tree additional time to absorb the leave nutrients.
Leaves respond to the shortening of the day and the decline in sunlight. The veins that carry fluid into the leaf begin to clog as a layer of cells forms at the base of each leaf. When this cellular separation is complete, the leaf is ready to fall. Fallen leaves are not wasted. They decompose and fill the soil with nutrients and become food for soil organisms. They are a vital part of the forest ecosystem.
Go out for a walk in the woods — and bring your camera — to enjoy this colorful season.