AUTUMN EQUINOX: The Changing of the Leaves

On Saturday, September 22nd at 7:04pm EDT, autumn will officially begin. A time of year when nearly all will venture forth to explore and witness the turning of the leavers from emerald and sage to various hues of amber, auburn, russet, magenta, and gold. For some people, fall foliage in the Bayshore region is a fixed event when families or individuals go walking and hiking in nature, or strolling on tree-lined streets to watch the brilliant leaf color. 

Unquestionably, one of the most asked questions during fall is what causes the leaves to turn color. Contrary to popular belief the arrival of the first frost or falling temperatures have little to do with initiating fall foliage. These actions mealy encourage what is already happening. 

To start explaining the development of autumn leaf color we need to go back to spring. A leaf has a limited life span. In spring, leaves develop from buds at the end of a plant stem. Leaves develop and grow during spring and early summer. As leaves mature they are arranged on a stem in one of three ways: alternate, opposite, or whorled. This arrangement affords the stem an equal distribution of leaf weight and prevents overlapping, so that each leaf on a tree can receive sunlight to perform photosynthesis.

Plant photosynthesis relies on the flow of energy and electrons initiated by light energy to create food, energy, and green color to a plant called chlorophyll. The literal meaning of the term photosynthesis means to build with light. 

On June 21, we experience the longest day and the shortest night of the year. From that date forward, the days become shorter and green plants, which depend heavily on sunlight for photosynthesis, begin to change, as plants start to store food to survive winter and early spring. 

In autumn, the amount of daily sunlight rapidly decreases and these changes start to become noticeable. Changes begin in the weakest part of the stem, which is at the base. The cells in the base begin to break up and die. This action decreases the flow of water, food, and minerals to the leaf. Eventually, trees withdraw their food and minerals altogether from the leaves to store them in permanent sections of a tree. 

As deciduous trees stop circulating food to stems, the green chlorophyll in the leaves disintegrates and is not replaced. When chlorophyll disappears, other colors or pigments that are always present throughout the leaf's lifetime can be seen. Some pigments include: yellow xanthophyll (which is the pigment responsible for the yellow in butter and egg yolks), yellowish-orange carotenes (which can be found in carrots), and red and purple anthocyanins (which can be found in many flowers and in some insects). Leaves may also contain tannins, which furnish a golden-yellow color in autumn.

In maple leaves, a high percentage of sugar or glucose results in the development of anthocyanins and the production of vivid colors in the leaves. The more sugar that is produced, the brighter red the leaves turn. The following spring this sugar in the tree will help to make maple syrup. 

The degree of color each autumn depends on many factors, such as water and weather conditions. Leaves directly exposed to the sun may turn red, while those on the shady side of the same tree may turn yellow. Eventually all pigment production in trees stop, and leaves turn brown. When the leaf is disturbed, as by wind, it breaks off the plant and falls to the ground. 

I hope you enjoy nature's most colorful show!

sosap2002@home.com - contact Joe Reynolds

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