Typically, leaves of deciduous trees and shrubs drop off in the fall, often after changing color. However, sometimes these leaves—or more commonly, some of these leaves—remain on the plant into and even throughout the winter. They are dead and brown by then and really stand out compared to nearby trees and shrubs that are completely bare at that time of year.
This phenomenon is called “marcescence” and some trees and shrubs are more prone to it than others, especially those in the Fagaceae family (oaks, beeches, hornbeams, etc.). Often, it’s more evident on younger subjects. They then become less subject to marcescence at maturity. In a beech wood, for example, most saplings have some marcescent leaves, but mature trees rarely do.
Marcescence is particularly common when a long, exceptionally warm fall comes to a sudden end with a deep frost. In that case, even species that are rarely marcescent suddenly become so. It is as if the plants had not yet finished their photosynthesis for the year and were caught unawares by the sudden arrival of cold.
You might notice that plants imported from other climates are more prone to marcescence than native species. It is as if they have not yet fully learned how to respond adequately to the vicissitudes of the local climate. In my region (Quebec, Canada), for example, the columnar English oak (Quercus robur ‘Fastigiata’), of European origin as its name suggests, always remains covered with dead, brown leaves all winter while in its country of origin, it rarely does so.
A Problem?
Marcescence is essentially considered to be of little consequence for the plant that “suffers” from it. In rare cases, branches can be pulled off during a snow or ice storm as dead leaves add to the weight of the branch and collect more snow and ice than usual, but that is still rather rare.
What to Do?
No, you don’t have to go over the tree or shrub removing the dead leaves one by one. Sometimes marcescent leaves are torn off by wind or snow during the winter. Otherwise, wait until spring and they’ll fall off on their own, pushed out by the branches’ expanding leaf buds that need the space. It may happen that a few brown leaves remain on the tree part of the summer, but that’s of no consequence.
Marcescence: a somewhat unusual phenomenon, but still totally natural. Just let Mother Nature take care of the situation.
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