Friday, November 16, 2012

Where's the Color?

     A friend of mine was walking in the woods the other day and asked me, "Where's the color?"  He had seen lots of very colorful leaves along the road going to the park, but once he was in the park there seemed to be very little color.  He was actually a bit disappointed not to be wowed from the color along the path.
     Imagine his surprise when I pointed up.  The color in a forest is not at eye level, it is above your head in the canopy.  There is plenty of color along the road for the same reason.

     First of all, the bulk of the leaves are in the canopy, which for a mature forest is above your head.  There are plants that grow under the canopy and some of them do change color, but the main body of leaves is above your head.  Along the road, trees will have leaves going all the way to the ground.  This is because the road creates an opening in the forest allowing light to enter.  Trees will grow leaves where there is enough light to support their needs.  So, along the road the canopy in not only above your head it is in a vertical plane paralleling the road.
     The color in the leaves is also a function of the kind of tree and where the leaf is located on the tree.  Some trees will simply always turn yellow.  No matter where the tree is located or what is going on with the weather, they will simply turn yellow.  This is because they turn yellow when the days grow shorter.  With a shorter day, they are not able to manufacture enough chlorophyll and over time they use up the chlorophyll that they have stored in the leaves.  As the chlorophyll amounts drop in the leaves, the other two pigments in the leaves - carotin and xanthophyll - begin to show because they are no longer masked by the green of the chlorophyll.
     Other trees actually manufacture pigments based on the amount of water that they have in their system, the amount of warm sunshine they get during the day, and the amount of nighttime cooling.  The red pigment, anthocyanin, is produced in the leaves of certain trees when they are exposed to warm, bright fall days so that they can produce a good deal of sugar and then cool nights where temperatures drop below 45 degrees, trapping the sugar in the leaves.  These trees will actually not color evenly.  Each part of the tree will change color depending on the amount of sun and cooling that they receive.  Thus leaves at the top of the tree that get more sun will be more colorful than those in the lower parts of the canopy that are shaded by the upper canopy.  Likewise, leaves at the top of the canopy will also be less protected by the surrounding leaves and more subject to temperature drop.  This is also true along the edges of clearings like the area along a road.  Thus the brightest colors will be at the top (or along the roadside).
     Most people will appreciate a fully yellow tree, but they will be much more excited by a bright red one.  Red is simply a more intense color that draws the eye.  If it is exciting red leaves that you are searching for when you are wandering in a forest, then you will need to walk with your head tilted back a good deal of the time.  The brightest color is up in the canopy.

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