Educational - Leaves
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Public information statement National Weather Service St. Louis, MO 10h30 CDT on THU, OCT 14 1993
How leaves change color
Many people suppose that Jack Frost is responsible for the color change in leaves...But not so. Many leaves begin to turn before we have any frosts. Change in coloring is the result of chemical processes which take place in the tree as the seasons change.
During the spring and summer a food-making process takes place in the leaf in cells containing the pigment chlorophyll. This gives the leaf its green color. The chlorophyll absorbs energy from sunlight and uses it in transforming carbon dioxide and water to carbohydrates...Such as sugars and starch.
In the fall the decrease in intensity and duration of sunlight and the cooler temperatures cause the leaves to stop their food-making process. The chlorophyll breaks down...The green color disappears and the yellowish colors or pigments already in the leaf become visible. The autumn foliage of some trees are mostly yellow colors including aspen...Birch...Hickory...White Ash...American Elm...Beech...Yellow Poplar and Willow.
From the sugars trapped in the leaves a red pigment is often formed. Trees with red or scarlet leaves in autumn are Red and Silver Maple...Dogwoods...Sweetgum...Red Oak...Black Oak...Scarlet Oak...Sumac and Sassafras.
Autumn weather conditions favoring the most brilliant colors are warm sunny days and cool...But not freezing...Nights. A few hard frosts can cause the leaves to wither more quickly and drop to the ground. The degree of color may also vary from tree to tree. Leaves directly exposed to the sun may turn red...While those on the shady side of the same tree or other trees may be yellow. When there is much warm...Cloudy and rainy weather in the fall...The leaves may have less red coloration.
We hope you have a chance to appreciate natures brilliant show of colors this autumn.
--Thomas
