Missouri's Season of Splendor

Indian summer, with its clear, sunny days and cool, crisp nights, is an almost irresistible lure to those who enjoy the outdoors. Without the bugs and humidity of summer, a hike in the woods becomes a more pleasant pastime. This type of weather also provides the ingredients for Missouri's most spectacular season-fall.

Pity the many people of the world who are not able to witness this changing of the seasons. In the tropics, where wet and dry seasons mark the year, the trees have no color change. Only the temperate hardwood forests give us this annual splash of color.

Picture Mother Nature going about on autumn days with a liberal supply of paint, coloring the leaves of trees to produce the brilliant displays of red, purple, orange and yellow. Every fall we enjoy the beauty of the forest, knowing it is only a passing pleasure. Before long, the leaves will drift to the forest floor to add to the rich carpet there.

Many people suppose Jack Frost is responsible for the color change, but he is not. Some leaves begin to turn colors before we have any frosts. According to a Native American legend, celestial hunters slew the Great Bear in the autumn, and his blood dripping on the forest changed many leaves to red. The fat that splattered out of the kettle as the hunters cooked the meat turned other trees to yellow. Other peoples had legends, but now we know that the changes in colors are the result of chemical processes that take place in the tree as it prepares for winter.

Trying to predict the peak of fall color is difficult. Missouri is blessed with a great variety of trees, shrubs and vines. Their leaves turn at different times and, as a result, Missourians enjoy a fall color season that may last four to six weeks. Sassafras, sumac and Virginia creeper are some of the earliest to change. They begin to show their fall colors by mid-September. By late September, blackgum, bittersweet and dogwood are changing.

The peak of fall color in Missouri is usually mid-October. This is when maples, ashes, oaks and hickories are at the height of their fall display. Normally by late October, the colors have faded and the leaves are beginning to drop from the trees.

This progression of color change starts earliest in north Missouri and moves southward across the state to the Bootheel. Generally, the color change is predictable but varies from year to year. Much depends on the weather.

A warm, moist growing season followed by a mild late-season drought sets the stage for a brilliant fall. During September and October, chilly, but not freezing, nights and sunny days are needed to bring out the best colors. These exacting conditions are not met every year, so some years are better than others.

Long periods of rainy and cloudy fall weather result in drab colors because of the low light intensity. On the other hand, trees under drought stress will often drop their leaves without showing much color.

Temperature also affects fall color. Warm temperatures encourage late season chlorophyll production that keeps the leaves green. A belowfreezing cold snap will kill the leaves before they turn to their fall colors. Even though the colors may be bright, heavy rain or high winds during the peak of color will cause the leaves to drop early.

The usefulness of the leaves does not end when their colors fade. Fallen leaves contain large amounts of minerals, such as nitrogen and phosphorus. Decomposition of the leaves returns these nutrients to the soil while adding a water-absorbing layer of humus to the forest floor. Shedding its leaves is another way a tree prepares for winter. Without leaves, broadleaf trees are better able to hold the weight of ice and snow on their branches.

Will October's colors be better or worse than last year's? Will we have a brilliant display of reds, yellows and oranges or one of faded browns? Sorry-but only nature and time will tell.

Why Leaves Change Color

Throughout spring and summer, leaves serve as factories manufacturing the food necessary for a tree's growth. The food-making process takes place inside leaf cells, in tiny structures called chloroplasts. The chloroplasts contain chlorophyll that gives the leaf its green color. The chlorophyll absorbs energy from sunlight and uses it to transform carbon dioxide and water to carbohydrates, such as sugars and starches.

Chlorophyll is unstable and must continually be replaced. Light is essential for chlorophyll manufacture. The tree's nutrition also affects the amount of chlorophyll in the leaf. If nitrogen, iron, magnesium or some other element is scarce, the rate of chlorophyll formation will decline. Restoring these nutrients will increase chlorophyll production. This is why shade trees often "green up" after being fertilized.

Other structures in the leaf called chromoplasts contain nonphotosynthetic pigments. These pigments are the carotenoids, the carotenes and xanthophylls that color carrots, corn, squash and bananas. Most of the year the carotenoids are masked by a greater amount of green chlorophyll. But in the fall the food making process stops. The chlorophyll breaks down, the green color disappears, and the yellow colors become visible.

Carotenoids tint the leaves of hardwood species, such as hickory, ash, maple, tuliptree, birch, cottonwood and sassafras.

A third group of pigments found in leaves are called anthocyanins. These pigments produce the reds and purples we see in fruits, such as apples, grapes, blueberries, cherries and plums. Anthocyanins are not present in the leaf during the growing season like the carotenoids. They develop in late summer in the sap of the cells, formed by chemical reactions between accumulating sugars and organic compounds called anthocyanidins.

Light is necessary for the formation of anthocyanins. Warm, sunny days followed by cool nights are ideal for their production. Sugar is made in the leaves during the day, but cool nights prevent movement of the sugar from the leaves. The brighter the light during this period, the greater the production of anthocyanins, and the more intense the colors. In trees with acid sap, reds will predominate; in alkaline sap, blues and purples prevail.

Anthocyanins temporarily color the edges of some young leaves as they unfold in the early spring. In our autumn forests, they show up vividly in maples, oaks, sweetgum, dogwood and blackgum. These same pigments often combine with carotenoids to give the deeper oranges, fiery reds and bronzes typical of many hardwood species.