Tree Facts: Fall colors

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Farm Forum

In autumn the leaves of many broadleaf shrubs and trees change color and we get to enjoy their beauty. The mixture of yellow and orange with a touch of red and purple is the result of chemical processes that take place in trees as the seasons change from summer to winter.

During the spring and summer the leaves serve as factories where most of the foods necessary for the tree’s growth are manufactured. This food-making process takes place in the leaf in numerous cells containing chlorophyll, which gives the leaf its green pigment color. Chlorophyll transforms sunlight into energy and combines carbon dioxide and water making sugars and starches causing trees to grow.

Besides chlorophyll leaves contain carotenes and xanthophyll which contain yellow and orange pigments. These colors are masked most of the year by great amounts of green coloring.

During late summer and early fall the connection of the leaf at the branch slowly changes as a layer of cells slowly dries up stopping the flow of water and nutrients to and from the leave. The clogged vessels hinder the making of the green chlorophyll. When chlorophyll production is slowed or stopped, the leaves lose their green color. As the length of daylight and temperature, decrease, chlorophyll breaks down, the green color disappears, and the yellow to orange colors become visible and give the leaves part of their fall splendor.

Cottonwood, ash and elm show only yellow colors, others like many oaks, display mostly browns. At the same time other chemical changes may occur, which form additional colors through the development of red anthocyanin pigments. All these colors are due to the mixing of varying amounts of the chlorophyll residue and other pigments in the leaf during the fall season. Some mixtures give rise to the reddish and purplish fall colors of trees such as maples, dogwoods and sumacs.

Temperature, light, and water supply have an influence on the degree and the duration of fall color. Low temperatures above freezing will favor anthocyanin formation producing bright reds in maples. The brightest colors are formed during bright sunny days rather than dull cloudy days. The richest colors occur when there is a quick change in temperature from high summer to lower autumn temperatures. Many leaves do not turn colors before the first frost. However, early frost will weaken the brilliant red color. Rainy and/or overcast days tend to increase the intensity of fall colors. The best time to enjoy the autumn colors is on a clear, dry, and cool day.

My sources for this news release were the State University of New York and North Dakota State University Extension. If you would like more information about “Fall Colors,” contact Bob Drown @605-244-5222 Extension 109 or by e-mail at robert.drown@sd.nacdnet.net.