Autumn Splendor

       As I look out my window, I see brilliant red leaves of the Virginia Creeper climbing a smoke tree whose leaves are still green.  And the nearby red maple is autumn  in progress.  While most of the maple’s leaves are mainly green, red is making prominent inroads.  The ends of the branches are reddening first, with the very tips the brightest red.  Closer in toward the trunk are a mass of leaves, all somewhere between orange and red.  And closest to the trunk are the greenest leaves.  But their green is now dull, a shadow of the bright green of summer.  And many of these leaves are showing hints of orange and red.  

     Who doesn’t love the reds, oranges, and yellows of fall?  Now that it is late October, and the colors are becoming dramatic, I try to remember what I learned long ago about why leaves from deciduous trees change color before they fall off the trees.  Since I’ve forgotten most of what I learned, I decided to consult a book that I like very much.  It is Mountain Nature:  A Seasonal Natural History of the Southern Appalachians by Jennifer Frick-Ruppert.  While the author, an associate professor of ecology and environmental science at Brevard College in North Carolina, focuses on the swath of mountains that extend from Virginia to Georgia, the processes she describes may be applied to color-changing deciduous trees  everywhere.

     The leaves of deciduous trees are green during most of their short lives (and being green seems pretty easy for them).  The chlorophyll contained in the leaves makes the leaves appear green because they reflect the green portion of the light spectrum, Frick-Ruppert explains.  Leaves contain other pigments as well–orange, yellow, and red, for example.  But those pigments are not visible to our eyes during the spring and summer months because the orange, red, and yellow portions of the light spectrum are absorbed by the leaves.  

     Chlorophyll is vitally important in the life of a tree because it converts light from the sun and carbon dioxide from the air into carbohydrates which the tree needs for nourishment.  Surprisingly to me, sunlight also degrades chlorophyll.  But in the fall, when days are shorter and colder, trees’ production of chlorophyll wanes.  And the chlorophyll in the leaves breaks down.  As chlorophyll disappears from the leaves, the other pigments that were there all along–the reds, yellows, and oranges–then become visible.

     Frick-Ruppert answers a question I have long wondered.  Why are some falls more brilliant than others? 

     A warm, wet summer, she explains, “ensures that every leaf is packed with pigments and every tree is loaded with leaves, setting the stage for a spectacular show.”  An autumn cold snap can accentuate the colors, she says, because it causes a rapid breakdown of chlorophyll.  Dry weather can also intensify the colors, she says, because anthocyanin, a substance present in sap, becomes more concentrated as the water in the sap evaporates away.  And since sunlight also destroys chlorophyll, sunny fall weather can also add to fall brilliance.  So the best color show occurs during a fall that is dry, sunny, and cool at night, according to Frick-Ruppert.  “When these conditions are met,” she writes, “a short but spectacular show results, and it is the timing of the cold snap that determines when the show begins.”–April Moore  


2 Responses to “Autumn Splendor”

  1. Joan Brundage Says:

    Thanks for the explanation. I’ve always wondered about the “why” of Autumn colors. I plan to enjoy the colors this weekend here in Arizona.

  2. Livvie Mellan Shapiro Says:

    Thanks so much for this… it only enhanced my enjoyment! Lovely fall reds and oranges in places in DC right now!

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