Nature and people can be fickle and / or a creature of habit, and when our habitual summer fun comes to a close, nature’s yearly ritual is just about to begin. This is the time that people from coast to coast tend to drive towards areas that display such vibrant colors not seen at any other time during the year. The spectacular change of landscape is the result of three factors: temperature and moisture, length of night and leaf pigments. So what is leaf pigment? It is matter found in a plant’s cells or tissues that gives it it’s natural coloring. Broken down further, the four pigments responsible for leaf color and its change in the autumn season are Chlorophyll, Carotenoids, Tannins and Anthocyanins. So what are these four pigments and how do they give us a cornucopia of color from late September to early November?

Photo Credit: AP Photo/Danny Johnston

Out of all of them, the most well known pigment is Chlorophyll. This chemical absorbs sunlight, which is necessary for photosynthesis, a process where carbon dioxide and water are transformed into sugar, which the tree uses for food. During the spring and summer months, chlorophyll is continually being produced and destroyed, giving the leaves a green appearance. When fall arrives, the leaves food-making process slows and the chemicals Nitrogen and Phosphorus are withdrawn from the leaves, to be stored in branches during the dormant winter period. With the loss of these chemicals, along with the reduced exposure to sunlight, the production of chlorophyll is stopped, and the green color in the leaf fades away. The Tannins and Carotenoid pigments are always present in leaves, but not visible for most of the year. Carotenoids are responsible for the yellow and orange colors that appear on different species of trees and when a tree’s leaf goes brown, the pigment responsible is Tannins. Both pigments only become visible when chlorophyll disappear from the leaf. Tannins are bitter substances responsible for the color and flavor of tea. Lastly, Anthocyanins are a pigment seen in Dogwoods, Sourwoods, Oaks and Maples and they are either seen as red, pink, or purple leaves. This is also the chemical that gives color to cranberries, red apples, plums, cherries and concord grapes and is usually not present until they are produced in the autumn.

A second reason for seeing the change in color during the fall months is when there is a change in temperature and/or moisture. As the days get shorter, temperatures trend downward and the colder temperatures help to bring about a corky tissue, which starts to grow between the branch and the leaf stem and interferes with the flow of chlorophyll to and from the leaf. When this occurs, the green of the leaf starts to diminish due to its lack of food supply and is replaced with another pigment color depending on the species of tree. The amount of moisture in the soil or lack of; also effects a trees turning process. If the spring/summer season is dry and/or warm, then the colors produced are usually red, pink or purple, due to an increase in their pigment Anthocyanin. If a spring/summer season tends to be overly rainy and cloudy, then the color intensity is reduced due to a lack of maximum lighting needed for photosynthesis. Additionally, a early frost is deadly if you wish for a vibrant color scheme, as the cold severely injures the leaves before the pigments reach their maximum development. Ideally then, warm and sunny days and cool, crisp night seem to bring out the best colors.

A third factor in seeing the change in color during the fall months is the length of night. From the middle of summer, to the heart of the fall season, nighttime is increased by about 2-4 hours, as the sun’s height in the sky is lower. The increase in darkness helps the corky tissue, mentioned above, completely cut-off the flow of food to the leaf and it dies. As a final act, the leaves fall to the ground, decompose and give the soil needed nutrients for the winter season.

Named the Long Night Moon because it’s the first full moon to follow the winter solstice, it’s also known as the Cold Moon. (AP Photo/Charlie Riedel)

So where and when is the best time to view these sensational colors? The answer to that question varies as does each season, but typically, since leaves turn based on shorter days and cooler nights, latitude and elevation above above sea-level determine which areas see the change in colors first. This is due to the fact that higher latitudes and elevations are the first to see the colder air late in the year. In the Northeast, the states of Vermont, New Hampshire and Maine, see the first signs in change of color, compared to the Southeastern U.S., where states such as South Carolina, Georgia and Florida are in a tropical climate, and the change in leaf color is either low to practically non-existent due to the milder winters.