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An Illinois River Almanac

Jason Haupt's Energy and Environment Blog
 MG 2276

Scenic Science


If you were to do a search for poems about autumn, you would find hundreds from which to choose.  The beauty of the season has been expressed by poets and authors alike depicting its splendor in the most descriptive words.  The colors of the trees move from bright and vibrant greens to brilliant explosions of red, orange, yellow and many colors in between.

Fall is my favorite time of year.  Going outside in the cool weather to see a fireworks display in slow motion is more enjoyable to me than most other experiences in nature.  But let me ask you, have you thought about the process that creates the bright explosions of color?

Chlorophyll is what gives the trees the green leaves. As the days start to get shorter, the trees take a cue and begin to form a layer that seals the leaf off from the rest of the tree.  This layer restricts the flow of materials from the leaf to the tree and from the tree to the leaf.  Because the length of the periods of dark each day is the cue for changing leaves, it means that the leaves will start to turn at about the same time each year.

If you remember your earth science, green plants produce chlorophyll.  This is how they perform photosynthesis.  Chlorophyll breaks down in the presence of light, however, it is replaced throughout the tree's growing season.  In the autumn when the connection between the tree and the leaf is broken, the materials that are needed to replace the chlorophyll are no longer available.  The chlorophyll in the leaf breaks down quickly and reveals the autumn colors.

The yellow and orange pigments of leaves are present throughout the year but are overpowered by the chlorophyll.  As the chlorophyll is broken down, the yellows and oranges become visible.  The red and purple pigments are produced from the sugars that are trapped in the leaves once the leaf is cut off from the tree.  Eventually the yellow, orange, red, and purple pigments break down only leaving the brown tannins in the leaf.

Temperature, moisture and sunlight have an influence on the quality and length of the display of fall color.  Sunny, cool days cause the chlorophyll to break down quickly. Cool temperatures at night with lots of sunlight during the day promote the production of the red and purple pigments.  Cool nights, warm sunny days and dry conditions during the autumn are ideal conditions for a spectacular display of fall leaves.  Cold temperatures at night that produce frost break down the mechanisms that produce the red and purple hues.  Early frost means an early end to the fall colors.

Armed with this knowledge, you should be able to go out and view the brilliant colors that trees in fall have to offer.

Please contact Jason Haupt (jdhaupt@illinois.edu) for more information or if you have any questions.

 



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