Part of the allure of fall foliage is color variation. There are trees
that turn red, purple, yellow, orange and brown.
Specific plant pigments determine individual colors. Foliage derives its
normal green color from chlorophyll, the substance that captures the
energy of the sun. Other pigments produce fall colors. Reds and purples
are caused by anthocyanins, yellows by xanthophylls, and oranges by a
combination of carotenes and xanthophylls. Browns are the result of
tannins present in the leaf. Most of these substances are present
throughout the growing season but are masked by the green color produced
by chlorophyll. Anthocyanins are the exception and are produced after
the chlorophyll is destroyed in the fall.
If you have ever seen pictures of New England in the fall, you have
probably wondered why trees in Kansas usually do not color as well. This
difference is partly because of the tree species prevalent in New
England. Certain oaks and maples naturally produce good color. Coloring
also is influenced by the weather.
Warm, sunny days and cool nights are ideal for good color. The sunny
days encourage photosynthesis and, thus, sugar accumulation in the
leaves. As fall progresses, each leaf develops an abscission layer at
the base of the petiole, or leaf stem, that prevents these sugars from
being transported down the trunk to the roots for storage. This high
sugar content in the leaves produces more intense colors. Cloudy days
and warm nights prevent some of the sugar accumulation in the leaves and
results in less vibrant colors.
Weather during other parts of the growing season also can have an
effect. Heavy rains in the early spring or hot, dry weather during the
summer can both have a deleterious effect on fall color.
The length of time a tree maintains fall color also depends on weather.
Reds, yellows and oranges are short-lived when trees undergo frosts and
freezes.
By: Ward Upham
