More on Winter Retention of Oak Leaves

Today I received two new comments on my ‘Winter Scene’ post that I think deserve their own post. The first is from June, who luckily has many squirrel-planted oak trees on her property and I just happened to have a photo of the one she mentioned that I took in mid-November.

Thanks, Pat, the trees are beautiful — I have a lovely white oak planted by the squirrels by our driveway that is beautiful now — in fact it won a prize at our last WOs meeting. June

The next is from Valerie Blaine, Naturalist with the Kane County (IL) Forest Preserve:

I wrote about marcescence, the retention of oak leaves throughout winter, in my October 2006 column.

I don’t think that column is on-line anymore, but here’s an excerpt from my files:

Maples do it. Hickories do it. Elms do it. Ashes do it. Oaks, however, are reluctant when it comes to letting go of their leaves. The habit of dropping leaves all in one season is called “deciduous,” and all of our native deciduous trees except the oak give up their leaves in the fall. Oaks either didn’t read the book or don’t have a calendar.

The usual pattern of leaf fall is determined by shortening day length in autumn, cold weather, and/or environmental stress such as drought and disease. In fall, most deciduous trees form a layer of cells near the base of the leaf stalk, called an abscission layer. The cells in the abscission zone put out a chemical that severs the leaf from the tree, while at the same time a protective layer is formed to seal off the twig, preventing infection.

In oaks, the abscission layer forms but is not completely functional. The brown, withered leaves hang on the tree, battered by wind and making cold shivering sounds on frigid winter nights. Spring comes with a burst of energy and a consequent swelling of buds. Cork cells form a protective layer as buds are expanding, and the bursting buds finally push the old leaves from the twigs.

There’s a term for oak’s aberrant deciduous behavior, one of those words you can toss around at your next cocktail party: “marcescence.” But fancy words notwithstanding, the better explanation may be found in a Seneca legend, as re-told by Dr. Andrew Hipp of the Morton Arboretum in his paper “When Oak Leaves Fail to Fall.” As this legend has it, “oak trees hang onto their leaves in defiance of winter, and the pine trees stand in alliance with them.” Sounds good to me.

Valerie Blaine

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