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Predicting Autumn Color

Dry fall following wet summer makes a good show

This year will bring spectacular fall foliage coloration — provided it stays dry.
    That’s what I told the Bay Weekly reader asking for my prediction.
    More rain means that more of the leaves will remain green for a longer period of time, thus reducing the intensity of the red, orange and yellow. If we have a dry fall, a higher percentage of the leaves will turn color at the same time. But because of drier conditions, the foliage will not last long.
    This prediction is made based on our abundance of rain that kept the foliage lush all summer long. Thus, the leaves of deciduous trees have generated an abundance of carotene and anthocyanins, the pigments that generate the red, yellow and orange colors in leaves. Those compounds are present in each leaf but masked by chlorophyll. That chlorophyll deteriorates as days cool and daylight hours shorten, and nitrogen — a major component of chlorophyll — migrates from the leaf tissues down the petiole to accumulate around the vegetative bud at the base of each leaf. 
    In years with a dry growing season, foliage is less lush, and deciduous trees have less foliage. If a dry growing season is followed by a dry fall, the foliage will be bright but of very short duration. If the growing season is dry and we have a wet fall, the foliage will be muted but slow dropping from the branches.
    Not all tree species generate the same colors. Maple trees are known for their bright red and orange colors, while the ash tree is easily recognized by its yellow fall color. A hill in New Hampshire is called Red Hill because most of the trees growing there are sugar and red maples. That hill is highly visible; many make a yearly pilgrimage to see it.
    In southern Maryland, we are lucky because we have an abundance of dogwoods that often begin showing their red colors in late summer. Near wetlands, we have sweet gum and black gum, which contribute red to purple-red colors and are most plentiful. Red maples provide a splash of red to orange-red in both wetlands and on hillsides.
    If we have a dry fall, the scarlet oaks should be spectacular with their deep red leaves. Most of the other oak species provide only a limited amount of yellowing before dropping their leaves. 
    Enjoy.


Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.