Fall Foliage

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fall folliageOnly a few regions of the world are fortunate enough to have a beautiful display of fall foliage when the leaves of the trees change in the fall – Oklahoma is one of them. Some areas of the our state are known for especially beautiful areas. I live in “Green Country” and this is certainly one of them. This is one area of the United States with just the right combination of tree varieties, temperature, and moisture.

Temperature and Daylight Make the Difference

The way plants turn water and carbon dioxide into oxygen and sugar is called photosynthesis. Did you know that means “putting together with light”? A chemical called chlorophyll helps make photosynthesis happen.

The reason leaves of some deciduous trees change color is because variations in temperature and periods of daylight cause the leaves to stop their food-making process, photosynthesis. Photosynthesis takes place in cells of the leaves that contain chlorophyll, which gives the leaf its green color.

In the dead of winter, there is not enough light or (often) water for photosynthesis. The trees rest. (think hibernate) They actually live off the food they stored during the summer. They begin to shut down their food-making processes and the green disappears from the leaves.
Did you know that photosynthesis means "putting together with light"? Click To Tweet
Along with chlorophyll, leaves also contain orange or yellow carotenoids which, for example, give carrots their color. During most of the year, these yellowish colors are masked by the greater amounts of green coloring. In the fall, however, when photosynthesis stops, the green color disappears. The yellower colors become visible and make the leaves part of the fall splendor.

At the same time, other chemical changes may occur that cause the formation of additional pigments that anywhere from yellow to red to blue. Some of them give rise to the reddish and purplish fall colors of leaves on dogwoods and sumacs. When glucose (a sugar) stays in the leaf after photosynthesis stops, sunlight and cool night in combination cause these color variations. This is why sunny days in autumn make the most beautiful variety of fall foliage.

Sunny Days, Cool Nights, and Fall Foliage

The conditions that favor the most dramatic changes resulting in vibrant reds are warm, sunny days followed by cool nights when the temperature dips below 45°F. Familiar trees that turn red are flowering dogwood, many maples, sweetgum, oaks, and sumac. Leaves fall to the ground because a special kind of cell develops at the base of the leaf stalk where it is attached to the branch. Gradually, the tissues that support the leaf are severed.

Broad leaf trees use abscission to cut off the water supply to the leaves. They do this to conserve energy during winter. Trees store energy from photosynthesis in the roots and within the tree. The leaves of a broad leaf tree must fall off to conserve the water supply. Abscission prevents water from escaping and freezing.

Evergreens and Fall Foliage

Did you know that evergreens are able to conduct photosynthesis in winter because the cells in the needles are protected by a sort of self-made antifreeze carried in the tree sap? The cold temperatures and lack of sunlight cause the photosynthesis process to take place more slowly and it is not as productive as warm weather photosynthesis which is why some needles end of up falling off the tree.

Evergreens have tight and tiny stomata which helps prevent water loss. The leaves do indeed fall off, but it occurs at a continuous rate instead of falling off all at once. The large pores in broad leaves means water can escape and endanger the life of the tree: so, unlike evergreens, the deciduous tree must drop their leaves to conserve water supplies.

Elements in Leaves Return To Soil

Leaves contain relatively large amounts of valuable elements, such as calcium and potassium. When they fall to the ground and decompose, they return to the soil part of the elements used to make the tree grow. At the same time, the layer of leaves forms a water-absorbing humus.

While it is sometimes necessary to remove a heavy accumulations of leaves, they are perfectly fine left on the ground. If necessary, one of the easiest methods is to run over the ground with a lawnmower with catcher attached. The shredded leaves will make a most wonderful mulch around trees and shrubs or can be mixed with other yard waste in the compost pile where it will take up less space and decompose much faster than un-shredded leaves.

See the garden calendar for other ideas for your fall foliage accumulation!

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