Forest Hill Drive and Guerilla Hollow are closed on Sunday, May 25 due to high winds.

Natures Notebook: The Leaf That Refuses to Fall

By Bernheim

A marcescent oak
A marcescent oak tree

This time of year I like to take a leisurely hike through the woods whenever the weather permits.  I find the forest to be uniquely beautiful and peaceful.  The pace of many of the animals has slowed, the wildflowers have stopped producing their bouquets, and the leaves have fallen from the trees. Except, some haven’t.  They are still hanging on.  I’m not talking about our evergreen trees: the junipers, hollies, and others.  Rather, what I have noticed are the deciduous trees.  Those, that we all learned at an early age, lose their leaves in the fall.  So, what is it with those trees that are still hanging on to their brown and gold leaves in the heart of winter?

This characteristic is called marcescence. It is a common but poorly understood phenomena.  It is most often noted in this area with the American beech trees which are so common in our forests and  lawns.  But other trees can also be reluctant to drop their leaves.  Among these are some members of the oak family, some sugar maples, and hornbeams.  The science behind this is sketchy and far from certain.

To backtrack a bit, leaves fall when, with the approach of the colder part of the year, a layer of cells forms on the stems of trees to protect the stem during the colder months.  This “leaf scar” (the abscission layer) allows the leaf to fall away.  When it doesn’t fully form, the leaf hangs on, often until spring, when new growth pushes it off.  Why this happens is the mystery.

One popular theory, and there are several, is that the retention of dead leaves discourages deer and other animals from browsing on the tender branches.  That many indeed be part of the answer but it leaves many questions.  Why some species but not others?  Why on branches that are far too high for the deer to reach?  It is not a bad thing to have some unsolved mysteries in our lives.

Please enjoy a peaceful hike through the forest and take time to observe the trees – both those whose leaves now cushion and nourish the soil and those that just won’t let go.  Treasure the mysteries along with the beauty.

Ken Johnson, Volunteer Naturalist

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