Why Do the Leaves Only Change Colors in the Fall?

October 6, 2017

Dear Editor:

Autumn is a wonderful, colorful time of year.  The leaves of summer are dying off in a splendor of reds, yellows, and browns.  The falling of the leaves is a sure sign the colder days of winter are coming.

Which leads to the question, why do leaves change colors and fall off in mid to late October in Michigan?  Well, it not because the cooler days of fall, but because of the shorter days of autumn.

Photosynthesis describes how leaves trap sunlight, carbon dioxide, and water are convert them into an energy-rich fuel.  A minimum amount of sunlight, intensity and duration is required to maintain a plant’s ability to keep this “energy absorbing” reaction going.  So as the sun’s path across the sky becomes too short and too low, the plants turn their photosynthesis machines (chloroplast) off and begin to prepare for spring.  When the sun’s intensity returns, the cycle will begin, again.

As the trees prepare for the spring, they drain their leaves of their valuable resources (glucose and other essential nutrients) and store them in their roots.  Only the colorful skeleton and inner organs of the leaves remain, displaying the inner beauty of a leaf and all of their magnificence. These are the colors of fall.
There is a difference between leaves that are “picked” in the summer during the growing season and a leaves that “fall off” in autumn.  The picked leaf will die a quick death.  It has been picked off from it resources and can no longer survive.  So, it will quickly dry-out and turn brown.  The leaves of autumn have time to “move out”.  They are slowly cut off from their resources (sunlight) and have time to save anything they can.

It is kind of like a factory fire versus a factory relocation.  The fire is quick and devastating. It destroys everything leaving only the charred blacken remains.  Whereas when a factory relocates, it will leave an empty factory behind but there still is a structure.  Granted the structure is no longer working, but there still are some remnants of it.  Although abandoned factories can be quite the eye sore, abandoned leaves can be enjoyable eye candy.

So as you look at all the beautiful colors of fall, remember those colors have always been there, it is just that they have been covered up with all the busy actions of photosynthesis.

Let the leaves of fall be a metaphor of life.  The beautiful colors are ALWAYS there, we just get so busy we cannot see them.

Andrew J. Frisch
Science and Math teacher
Farwell High School

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