In the fall, all too soon for our liking, the foliage on most deciduous trees takes flight. Leaf fall is determined by changing chemistry in the tiny abscission zone, a narrow band of cells at the base of each petiole or leaf stalk, where it attaches to the stem or branch. The catalyst is a hormone called ethylene, better known for its role in ripening fruits. The restriction of ethylene’s destructive effects only to cells in the abscission zone illustrates the precise control trees have over their hormones.

Nowhere is this engineering prowess more astounding than in the deciduous trees that hold onto their dead leaves all winter, only to release them in the spring. To accomplish that, they must manage to keep only certain attachment points up and running until the following spring. Then abscission can be completed and the leaf falls. Wind may rip away some leaves in the winter but the petiole base doggedly hangs on. These trees are exhibiting marcescence (noun, “mar-SES-sense”), the trait of retaining plant parts after they are dead and dry.

Certain trees, including beech (Fagus), witch-hazels (Hamamelis), oaks, hornbeams (Carpinus), American hop hornbeam (Ostrya), and sugar maple are renowned for holding onto their withered leaves. Leaf marcescence is most often seen on juvenile trees and may disappear as the tree matures. It also may not affect the entire tree; sometimes leaves persist only on scattered branches or the lower part of the tree. But why?

The reasons for marcescence are not clear, though one theory argues it is a defense against browsing by large animals. A mouthful of dead leaves is a less-tasty target that a bare twig and tender buds, something today’s deer also seem to understand.

Scientists have found that spring-shed leaves were richer in soluble minerals than autumn-shed leaves that had been lying on the ground all winter, presumably because leaves held on the tree were drier and therefore less readily attached by fungi and microbes. When the leaves fall in the spring, the roots are active and able to uptake nutrients as they leach from the leaves. And keeping the leaves only on the lower branches improves the chances that they will fall within reach of the tree’s own roots.



Knowing a little botany can help us be better gardeners, and deepens our appreciation of how trees live their hardworking lives. Plus, a bonus tip: A row of marcescent trees, although not technically evergreen, makes for an effective nearly year-round screen.

American beeches are the most famous trees known for displaying marcescence.

Swamp white oaks (Quercus) with marcescent foliage at the World Trade Center Memorial, New York.

A red oak exhibiting marcescence. I love the contrast between the snow, the blue sky and the brown leaves.