Will it be a Colorful Fall--or Dull? ODNR Explains Why Leaves Change Color to Produce Ohio's Fall Spectacular
September 12, 1997
COLUMBUS, OH -- It's easy to enjoy the fall fireworks that turn Ohio's forests and roadside woodlands into a blaze of yellow, orange and red. But few Ohioans understand the complex scientific principles behind this yearly fall spectacular.
A brief explanation, according to Ohio Department of Natural Resources (ODNR) foresters, may help decide the age-old question: Will this be a colorful fall or a dull one?
During summer months, a leaf is green thanks to an abundance of pigments in the chlorophyll family, the ODNR experts explain. These green pigments capture energy from the sun, using it to manufacture simple sugars that are necessary for the tree's growth. The whole process is called photosynthesis, something most of us vaguely recall from 6th grade science class.
Photosynthesis steadily consumes the leaf's supply of chlorophylls, but that's not a problem in summer months when a tree replenishes chlorophyll at a steady rate. It's when days grow short and nights are cool that trees fail to produce enough chlorophyll pigments. As demand outstrips supply, the leafy green begins to fade. That allows other pigments -- which have been present in the leaf all along -- to show through the fading green. These are the carotenoids, producing hues of yellow, brown, and orange.
Other colors, including reds, purple and their blends, are created by anthocyanin pigments. Unlike the carotenoids, these pigments are not present in a leaf all year and develop in sap cells by late summer.
"Early autumn weather also plays a key role in determining the brilliance of fall colors," said Bill Schultz of ODNR's Division of Forestry. "A series of warm, sunny days with cool nights seems to bring out the most brilliant color displays."
According to Schultz, large quantities of sugar are produced in leaves during ideal weather conditions. When complemented by cool nights, the leaf's veins begin to close, preventing the sugars from being released. These conditions stimulate the production of the red and purple anthocyanin pigments, particularly in sugar-rich tree varieties such as maple, oak, sweetgum, dogwood and blackgum. When high levels of both anthocyanin and carotenoid pigments are present, leaves display the deeper oranges, fiery reds and bronzes that can light up a fall landscape.
Ohioans and out-of-state visitors who enjoy viewing the state's fall color in a variety of locations can call ODNR's Fall Color Hotline at (614) 265-7000 (for a recorded message, updated each Thursday) or the 1-800-BUCKEYE tourist information line for information on fall color conditions around the state. Internet users can find fall color information at ODNR's World Wide Web address: http://www.dnr.state.oh.us/odnr/color.
For further information contact Bill Schultz, Division of Forestry, (614) 265-6704, or Jim Lynch or Dave Pagnard, ODNR Media Relations, (614) 265-6886.