s the cooler days of autumn approach, North Carolinians anticipate the annual explosion of color when the state’s landscape changes from a sea of summer green to a full palette of brilliant yellows, oranges and reds.

While most people associate the changing color of the leaves with the cooler autumn temperatures, it’s not just the cooler temperatures that bring on the color display, according to Dr. Richard Braham, associate professor of forestry at North Carolina State University’s College of Forest Resources. It’s the results of those temperatures on the chemical processes in the leaves and the colors of the pigments already in the leaves that account for the change.

"The leaves of trees and other plants contain several different kinds and colors of pigments," Braham said. "The chlorophylls, which are involved in photosynthesis, are green. Some other main pigments in leaves are carotene, which is a yellow-red color, like a carrot, and xanthophyll, which is yellow. These pigments are present in leaves year-round."

During the growing season, Braham said, the chlorophyll pigments are abundant as they help manufacture food for the tree. "Because the chlorophylls, the green pigments, are so dominant and are continually being replaced, the leaves appear green during the spring and summer."

But as the temperatures turn cooler, this constant replacement of the chlorophyll pigments is inhibited, Braham said. "The cooler temperatures restrict this process to the point that the chlorophyll pigments ultimately disappear from the leaves. Basically what this does is unmask the other pigments, the reds and yellows, which were present all along, but in lesser amounts.

"Whenever you see a plant or tree in bright fall color, you know that it has little or no chlorophyll left," he said.

In other trees, these same processes occur, he added. "But in addition, another pigment called anthocyanin is formed in large amounts. Anthocyanin is responsible for the brilliant red and purple colors seen in some maples."

Getting the most brilliant fall colors takes more than just reducing the amount of chlorophyll in the leaves, Braham said, adding that year-round weather conditions and the general vigor of the tree also have an effect on the intensity of the fall color display.

"To get the best display of leaf color, we want to have fall conditions that will be cool to inhibit the reformation of chlorophyll, yet not so cool that the tree’s growth processes are stopped completely," he said. "What will give us the nicest color displays are warm days, but cool nights."

If the weather stays hot during the day and warm at night, then suddenly turns cold, the variety and intensity of the color can be limited, he said.  The amount of rainfall during the summer as well as during the autumn months can also affect the colors.

As people make plans to get out and see the year’s display of colorful foliage, Braham said, it’s important to remember that the colors will be showing for a period of four to six weeks. "People often have the misconception that the leaf color display in the North Carolina mountains only happens the second week of October," he said. "But in fact, leaves will be changing colors from mid- to late September into early November."

The sourwood and blackgum trees with leaves that turn reddish colors are usually the harbingers of the fall leaf color season, Braham said.

Braham, who teaches dendrology, or tree identification, said that in addition to the sheer beauty that the changing colors offer, there is also a practical side to the change in color. "If you know the color that a tree’s leaves change to in the fall, it can help you identify species that may be hard to determine.

"For example, the blackgum tree and the persimmon tree are very similar and are often confused. But if you know that the leaves of the blackgum turn a reddish color and the leaves of the persimmon turn a yellow or yellow-green color, then you can easily identify the tree in the fall," he said.

In North Carolina, yellow fall leaves can be seen on the yellow poplars, hickories, yellow birch, ash, black locusts, black walnut, and some maples. The show of red leaves comes primarily from the blackgums, sweetgums, maples, dogwoods and some oaks. The range and intensity of these colors can be spectacular, from brightest yellow and orange to brilliant red and deep purple-reds.

Many North Carolinians who are accustomed to the annual color display don’t realize that much of the world doesn’t experience this fall color change, Braham said. "Basically, eastern Asia and eastern North America are the only places where there are many species of trees and plants that have the brilliant color changes in the fall," he said. "There’s very little color change in the forests of Europe, for example, and Europeans are normally just astounded when they visit here during our fall color season.

"Other parts of the world, and even in the western United States, there may be only one or two species that change color. In our western states, there are the aspens that turn yellow and some maples that turn red, but that’s all. And because they have so many more evergreens, they don’t get the brilliant color displays," he added.

In North Carolina, most people don’t have to look far to see spectacular colors during the fall. With nearly 19 million acres of public and private forestland stretching from the mountains to the coast, there’s always enough fall color for everyone to enjoy.

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