Monday, October 4, 2010

Fall Color Change

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This time of year we are all watching for the fashion show that the leaves put on in the Ozarks.  Francis Skalicky wrote an excellent article in last week's News-Leader describing the mechanisms and variations of the change of leave color in the fall.
The common explanation you usually see is that the disappearance of chlorophyll leaves the yellow carotenoids and the red anthocyanins.  Francis goes on to explain the complicating effects of temperature, moisture and pH on color change.
Also, I never fully understood the factors in leaves dropping off the stems.
Just as weather in September and early October is critical to the formation of leaf color, weather in middle and late October helps determine how long we get to enjoy fall color.
That's because part of the autumn leaf-drop process trees go through is the abscission zone development that occurs between a leaf's stem and the branch it's attached to. Basically, this process consists of a hardening of cells in the leaf's stem and a similar cell-hardening that takes place in the branch.
As the two sides of the leaf-branch connection harden, an abscission zone -- also known as a fracture zone -- develops in the middle. The leaf-branch connection continues to get more brittle until the leaf eventually breaks free and falls to the ground.
If we have mild weather during the period when leaves are nearing the breaking-off point, fall color is a drawn-out affair that lasts for several weeks. If we have a heavy rain, strong winds or some other type of stormy event that drops a large amount of leaves, our fall color will be a much shorter experience.
The whole story is in the News-Leader article.

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