Autumn Fireworks...beautiful fall foliage
By: John Shepler
If nature celebrated her independence, wouldn't it be the same way we do? With a huge celebration, a tremendous visual display of color in the sky?
Welcome to autumn's brilliant independence party. Now the restful green of summer's productivity explodes into a harvest festival of yellows, reds, oranges and chocolate browns. Little ones and big ones, high in the treetops and all along the hedges. The leaves of fall are going out in flashes of color. Flashes that peak only for a few days and then flicker out as they wither on the ground.
While our Independence Day fireworks illuminate the heavens with much noise and sparkle, they awe us for less than an hour in the night sky. Nature's time scale is more relaxed, and far more filling of our visual environment. From late September until early November, there is a month's time set aside to celebrate the bounty of this year and prepare for the time of rest before the cycle begins anew in the spring. This is nature's big hurrah. "Hooray for us! We did it once again! We harnessed the energy of the universe and converted it to fuel the engines of life. Life in all its forms and glory has grown and prospered on the Earth. Thanks everyone. See you again next year!"
Science, man's explanation of why nature does what it does, misses the sheer wonderment and excitement of it all, but gives us some insight on how this cycle waxes and wanes with such regularity. There is a science of fall. It is the chemistry of autumn, the physics of foliage. As we change our viewpoint from the synthesis of life's grand celebration to the analysis of cellular interactions, we get to peek inside the living machines and see how leaves and trees and water and sunshine all communicate in nature's rhythm.
Why do the leaves change color and fall off the trees each year? Why shouldn't they just stay as they are, green and unvarying, year after year? In some cases, they do. Just look at the evergreens. Unless they are damaged by people or animals, or an unusually strong wind, they keep their needles, their type of leaves. The inner ones may die off from lack of sunlight, but there is a constant growth of new soft needles extending the perimeter of the tree each year.
Not so with the deciduous trees, our favorite elms and maples and oaks. Their annual life cycle is more dramatic. The reason has to do with the way the leaves are constructed. They are large and flat and thin, and full of moisture. In the depths of January's deep freeze, the watery sap surrounding the leaf cells would surely freeze, and the ice crystals would penetrate and destroy the cells. If the freezing action extended down the branches and throughout the tree, there would be no living tree come spring.
So nature's way is to seal off the hydraulic connection between branches and leaves, weakening the bond so that the leaf flutters away in the next available breeze. It has served its purpose well during the long days of summer. A leaf is actually a little sugar factory. The warmth and light of summer allow the leaf to synthesize chlorophyll, the green compound that gives leaves their color. Chlorophyll absorbs red and blue light from the sun which becomes energy, like the energy of a battery, to cause chemical reactions. In this case, carbon dioxide, the stuff we breathe out, is pulled from the air. The leaf uses it plus water from the soil to make chlorophyll plus oxygen, the stuff we breathe in. In this way plants and animals complement each other, so we both get what we need in an exchange of air.
Chlorophyll does something else for the tree, though. It also creates sugars and starches that are used as food by the tree, so it can grow and produce seeds. This process is called photosynthesis, the synthesizing or creating of chemicals from photo or light energy.
There is another photo term, photoperiodism, the response of a plant to the lengthening and shortening of daylight. Photoperiodism is what signals the onset of fall. As days get shorter and shorter, there is less sunlight to activate the leaves. The chemical factory loses energy and slows to a crawl. Less sugar and starch is produced, less chlorophyll is synthesized to replace what has degenerated. As the chlorophyll fades, so does the green color of the leaf. What's left are other chemicals, the yellow pigment of carotene and the red of anthocyanins. Oh, they were there all along during the summer. It's just that the intense green of the abundant chlorophyll hid them until it no longer could. Now, in the fourth quarter of the year, they burst forth to add their radiance to the sky and ground show of autumn.
So, who's to say? Are the fall colors we enjoy so much really nature's celebration of life's independence in a cold and barren universe, or are they simply the product of mundane chemical reactions acting in response to the wobbling of the planet on its axis?
Perhaps the Native Americans touched the soul of autumn's meaning in their myth of the hunters, who killed the Great Bear in the sky, spilling its blood on the forests and turning some of the leaves red. Some leaves became yellow, as the hunters cooked the bear's meat and dripped fat on other trees in the forest. This, too, is a story of life and the endless cycle of nature growing, harvesting and nourishing to grow again.
Also visit these related sites:
Why Leaves Change Color - A good explanation of where autumn colors come from in a question and answer format.
The Scientific Basis for Autumn - The process of photoperiodism, how changing sunlight brings on the autumn process. Provided by NCNaturnal, the North Carolina Living 'Zine.
The Chemistry of Autumn Colors - For science buffs who really want the formulas, they're here from the Science is Fun site by University of Wisconsin- Madison Chemistry Professor Bassam Z. Shakhashiri.
Why Leaves Change Color - This site, by Stormfax, includes the Native American myth of the hunters and the Great Bear. Also lists phone numbers to state and regional fall foliage hotlines.
Preserving Autumn Leaves - More thoughts on how to preserve autumn leaves and use them for decorating.
Indian Summer - Thoughts on the magic of those warm, dry, hazy mid-autumn days of pure beauty and temporary escape.
Arbor Day, J. Sterling Morton's Legacy of Trees - How one man's passion to beautify a treeless prairie led to a worldwide holiday of environmental awareness.
Copyright 1998 - 2017 by John E. Shepler. Contact me at: John (at) JohnShepler.com
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First Published: October 11, 1998 as part of A Positive Light