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OAK, BEECH LEAVES WILL FALL, BUT NOT UNTIL SPRING
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Ever wonder why some leaves stay on
trees long after other hardwoods have dropped their leaves?
Terry Karkos, in his “Back to Nature” article in the
Sun-Journal (Dec. 3, ’02), did some research and found two new words to
explain the phenomenon: abscission
and marcescent.
Marcescent
is an adjective that means, “remaining attached to a plant when
withered,” which applies directly to beech and oak leaves because they
hang onto their leaves throughout fall and winter.
Abscission is the natural process by which leaves or other parts
are shed from a plant and, it’s thought that with autumn’s decreasing
day length and cooling temps, certain cells at the base of the leaf change
and form a separate layer of thin-walled cells, called the abscission
layer.
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The decrease in daylight triggers growth-inhibiting hormones that build up at the petiole's (leaf stem) base and dissolves this layer soon after it forms. When nutrients in the leaves are extracted and return to the tree, the abscission layer forms the separation zone so the leaf can fall off as the wound is sealed.Unlike most hardwoods, in marcescent trees like beech and oak, leaf production continues unabated into the late fall. The abscission layer in marcescent trees never forms. These trees continue to produce sugars until freezing weather halts the process and the leaves wither and/or freeze in place. Thus, without the abscission process to loosen them, the leaves remain firmly attached until spring when new leaves emerge from their buds, forcing any remaining leaves from the twigs or branches. (University of Minnesota Extension Service and University of Georgia) |
Nature makes ready for spring. |
However, drought can trigger the abscission layer in marcescent trees, which explains why some beech trees still had leaves last Fall. Learn something new every day!
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