While gazing out the window, on a bright sunny February day, I noticed the neighbors swamp white oak (Quercus bicolor) tree is still holding onto its leaves. Yes, the leaves were brown yet still attached to the tree.

Come to think about it, that same tree had leaves that held on late last winter. Now isn’t that interesting?

I later started noticing other trees that have leaves that hang on over the winter and sometimes even into the spring. Besides the swamp white oak, this regular or yearly phenomenon occurs on other oaks (Quercus spp.), American beech (Fagus grandifolia), hornbeam (Carpinus caroliniana), Eastern hophornbeam (Ostrya virginiana), and witchhazels (Hamamelis species).

Have you ever wondered why these trees hold onto their leaves while other deciduous trees drop their leaves in the fall? Dendrologists or those who study trees call this phenomenon marcescent. Marcescent as defined by dictionary.com is the withering, but not falling off, as a part of a plant. Marcescent comes from marcescere, and in Latin, means “to fade.”

Abscission of leaves is commonly called leaf drop. Abscission comes from the Latin words ab (away) and sciendere (to cut), is a tightly controlled cellular progression that occurs at given developmental stages during the lifespan of a plant and ensures that plants can shed organs when they are no longer required – such as flowers after pollination or leaves on a tree.

Unfortunately, this isn’t a one- size-fits-all situation, but rather can occur in lots of different ways and times. This can even vary from year to year.

Some trees also are marcescent in that they may drop some leaves, but not others. If this occurs, trees will usually drop leaves from their upper canopy, but those lower limbs may hold on to their leaves longer. These persistent leaves do not readily form an abscission layer at the base of the leaf petiole, where it attaches to the twig.

This allows these brown leaves to remain attached on trees much longer, often to the chagrin of autumn-rakers who want to rake once a season and be done. My swamp or red maple (Acer rubrum) is notorious for this. I find myself raking maple leaves at least three times in the fall.

This type of marcescent activity occurs when we have a warm fall followed by a sharp drop in temperatures. Some trees did not have time to prepare themselves for the cooler weather, allowing the upper canopy to undergo abscission and the lower canopy leaves to remain attached to the tree.

Regular yearly marcescent leaves such as oaks, on the other hand, do not abscise until later in the spring of the following year. Normally this occurs when new spring growth encourages them to finally fall.

Dendrologists often question if marcescent leaves is either helpful, or harmful, when it comes to plant health. When there are a lot of leaves present over the winter with snow or strong winds, or the combination of the two, this could have some negative effects and lead to branch breakage.

Plant ecologists have their own theories. Some have suggested that leaves that drop later in the spring will provide a fresh layer of leaf mulch around the tree that helps conserve soil moisture in the spring.

Another theory that seems to make some sense is tied to wildlife, specifically deer. Experts believe that these trees hold onto these dry, unpalatable leaves to deter browsing by these four-legged hungry herbivores. Deer prefer to feed on the more tender and nutritious buds and twigs. It is thought that the bitter, old foliage will protect the tree from browsing activity.

To learn more about marcescent leaves on trees, Kansas State Research and Extension has created a YouTube video that can viewed at https://www.youtube.com/watch?v=u9dNHUKx2WQ.