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Why Do Leaves Change Color in the Fall?

The Science Behind the Scenery


Leaves Turn Color in Massachusetts in the Fall

Temperatures, precipitation and even tree genetics play a role in why leaves change color in the fall.

© 2003 Kim Knox Beckius
Want to know why leaves change color in the fall? The truth is... leaves don't really turn color. The colors are there all along!

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.

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 change 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.

To truly appreciate fall in New England, get in your car and drive out in the country, hike up the nearby mountains and hills, take a cruise along athe coast, or get on your bike and pedal the back roads.

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