Why Do Leaves Change Color in the Fall?
by Amy Hunt

Fall is finally here, and with it comes many opportunities to marvel at our beautiful world. Have you ever wondered what makes the leaves on trees turn to brilliant shades of different colors? If you are like me and really have no idea, read through this article and then impress your kids with your vast knowledge.

The Science Behind the Scenery

Deborah Fowles

Your Guide to Portland, ME

Leaves get their green color from chlorophyll, a pigment found in plant leaves that enables them to process sunlight. Fall's shorter days and cooler temperatures cause the chlorophyll to move from the leaves to the branches, trunk, and roots, and the yellow and orange pigments that are always present become visible.

Other chemical processes produce the brilliant reds, purples and bronzes. On warm fall days, sugar is produced in the leaves of some trees and then trapped by the chill of night. As sugar accumulates, the leaves turn brighter red.

Factors that influence the amount of fall color the leaves will wear each year include:

Rain

Amount of sugar in the leaves

Wind

Temperatures

Weeks of cool, bright sunny days and chilly nights (but no frost) create the brightest colors. The side of a tree exposed to bright sunlight might turn red, while the shady side of the same tree may turn yellow. And cool, sunny autumn days produce brighter colors than warm, wet weather.

Trees "inherit" their fall colors, just as we inherit the color of our hair. The color depends on how much iron, magnesium, phosphorus, or sodium is in the tree and the acidity of the chemicals in the leaves. Here are the "inherited" colors for some of our most common trees:

YELLOW (caused by the chemical xanthophyl) Ash, basswood, birch, beech, butternut, elm, hickory, mountain ash, poplar, redbud, serviceberry, willow, and some maples (boxelder, mountain, silver, striped, and sugar).

RED (caused by the chemical anthocyanin) Some oaks, some maples, sumac, and tupelos.

ORANGE (caused by the chemical carotene) Some oaks and maples.

RED OR YELLOW Sugar maple, dogwood, sweet gum, black gum, and sourwood.

New England enjoys some of the most intense fall colors thanks to its almost pure stands of a few types of trees that all turn color at the same time. Trees are not the only thing that contribute to a colorful autumn, though. Shrubs like burning bush and sumac, and even weeds like poison ivy can paint the roadsides brilliant colors in fall. In Maine, the blueberry barrens turn a phenomenal fiery red.