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Autumn Leaf Drop, and Why Some Trees Don't Drop Leaves
Published: 12/13/2022
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By now, Michigan is transitioning into a winter landscape with the leaves of many trees having dropped already, leaving the bare branches ready to be blanketed in snow. Deciduous trees losing their leaves is a vital process in their preparation for winter. The tender leaf tissue would be the part of the tree most vulnerable to freezing, thus leading to potential damage spreading to the rest of the tree. How do the leaves fall in the first place? The trees begin to form a barrier between the leaf and the stem called an abscission layer. This barrier will protect the tree from winter frost, and when it is fully formed, the leaf will no longer be attached to the tree and will fall. The layer of fallen leaves on the ground will continue to remain beneficial to entire forests by providing a steady layer of decomposing nutrients. Curiously, many young oak trees do not form a full abscission layer, thus hanging onto their leaves, sometimes all the way into the onset of spring when new buds form. Oaks are not the only tree to do this, and there are varying thoughts as to why the trees hold onto dead leaves through dormancy. One belief is that it protects the tree from grazing deer in the winter, as the phenomenon can often be seen on lower branches, whilst the upper branches have shed their dead leaves. Evergreen trees do not become bare in the winter, making it the iconic winter holiday tree. Their needles are coated in a wax called cutin that prevents the loss of water and damage of frost. Some species, like the white spruce, can handle cold extremes as low as 70 degrees Fahrenheit!