During the autumn months the leaves on deciduous trees turn colors and soon thereafter fall from the tree. But have you noticed that some species retain their leaves until spring? In central Wisconsin this is most common on oak and beech trees. The term for this leaf retention phenomenon is called marcescence, which basically means “hold on to stuff”. On a tree that loses it leaves such as maple, when the nights get longer and the days get shorter, the cells at the junction of the leaf and twig start to divide. This forms a layer of cells that slowly block the transport of carbohydrates from the leaf and nutrients from the twig. Ultimately killing the leaf and severing it from the twig. Ecologists have yet to figure out the exact reason that some species retain their leaves. With this lack of scientific evidence brings on some interesting theories and speculation to why this occurs.
Dry infertile sites are where we commonly find oak and beech trees. These soil conditions may play a role in why leaf retention is important to these species. Retaining leaves until spring would definitely slow the decomposition and would increase the organic material on the forest floor during the growing season for the parent tree. This could give that tree a competitive advantage on poor sites by increasing nutrition and retaining moisture on the forest floor.
Trapping snow could also be a reason for leaf retention. This would allow for more moisture on the forest floor during the spring when the tree is coming out of dormancy.
Another possibility for marcescence is to protect the tree from browsing animals. These dry leaves may be protecting buds. Since dry leaves are less nutritious than green leaves an animal is less likely to remove the brown leaf to gain access to the new buds that are formed underneath. This would be especially important to small trees.
These are just a few possibilities of why marcescence happens. We don’t know whether this provides a competitive advantage or if it is just a coincidence. But what we do know is that these leaves stay on until spring when new growth starts and the buds expand, pushing off the old leaf. This can make for a long noisy winter of rustling leaves in the wind if you have and oak or beech near your home. I hope this article shed some light on why some deciduous trees retain their leaves and others don’t.
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