Our Window on Nature

. . . exploring the world around us

Changing of the Colors

Filed under: Trees — Lowell Christie -- September 1, 2006 @ 8:11 pm

Maple LeavesIt’s hard to pick a favorite season. Spring with its blossoming wildflowers? Noisy summer with the song of crickets on a balmy night? Or winter, with its fellowship around the warmth of a fire? But autumn is a kaleidoscope, a last brilliant flash of color before the fallen leaves succumb to the smoky fingers of a bonfire.

Wherever we are, about mid-September we feel an annual urge to dash to New England to see autumn at its finest. Do you think it’s provincial snobbery when Vermonters boast about the Connecticut Valley in the fall? Then it’s certain that you haven’t been there, because New England’s autumn foliage is unsurpassed anywhere in the world. When you understand what makes the colors turn as they do, you’ll know why.

Everyone realizes that leaves are usually green, and that the verdant color comes from chlorophyll producing the materials of life. But green means spring, when the plant world is in full production. Autumn is different. Now plants and trees begin preparing for a colder season, when leaves are of little use and in some cases a distinct disadvantage. During the weeks that mark the boundary between summer and autumn, the chlorophyll used up in the leaves is not replaced, revealing the yellows of October and reminding us to tear another page off the calendar.

The yellow leaf pigments were present throughout the growing season, but were hidden by the green of chlorophyll. Now as the season progresses you see day-to-day changes in aspens, hickory and birch. First a lighter cast of green gradually eases into yellow, until oceans of gold cover the autumn mountainsides.

But the yellow colors are subtle compared to the red, orange and russet that burst upon your senses in a New England autumn. And these colors are newly produced; not something hidden that escaped your notice.

These shades of red are created by special water-soluble pigments carried in tree sap. It’s these same pigments that create most of the blues and reds in flowers. And as the color of your backyard hydrangea depends upon the acidity of the soil, the precise color of an autumn leaf depends upon the acidity of the tree sap.

But why is New England singled out for the most astounding intensity and variety of colors? It’s the only location with the exact combination of high sugar content in the leaves, low (but above freezing) temperatures, and abundant sunlight necessary to produce them. Let’s look at them one at a time

New England is the land of maples. And since maple trees are the source of that cold weather breakfast treat, maple syrup, it follows that they possess an unusual supply of sweetener. And this sugar is necessary for the most vibrant shades of red.

During the summer growing season extra sugar created in the leaves is carried to storage areas in the roots for use the following spring. But sugar must be present in the leaves to produce bright color and that’s where temperature plays a role. Low temperatures interfere with the normal transfer of sugar, so only with brisk weather consistantly below 45 degrees Fahrenheit will sugar be trapped in the leaves, and the reds of autumn appear.

The final element is sunlight. The red and blue pigments in the leaves respond to the rays of the sun, and the brighter the light the more vivid the colors. (You see an example of this principle in the fruit of an apple tree. Usually one side of an apple is a redder color. The reason – the red side had more exposure to sunlight.)

And that is the secret of New England’s fall foliage. Only there do you find the unique marriage of cold crisp nights (under 45 degrees), combined with clear days (an abundance of sun), and trees with a very high sugar content (sugar maples).

A cloudy year may produce less brilliant colors, but in any but a poor year they are well worth driving to see. Autumn is a magnificent season wherever there are deciduous trees, but for the sheer spectacle, at least once in your life, experience New England in the autumn.


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