Early fall is my favorite time of the year with crisp days, sunshine, and the splashes of color everywhere as the trees start to slow down for the winter. One day I noticed that all the oak trees still had leaves. All the other trees were bare, but the oak leaves had not dropped off. I wondered if my oak trees were either diseased or were fighting an insect infestation.

Armed with books from our library, what I found out was that my trees were undergoing a process called “marcescence” (pronounced “mar-CESS-enss”). The word comes from the Latin marcescere (“to fade”).

In our area, beeches, hornbeams, oaks, and witch hazels go through this. In most deciduous trees the cells between the twig and the leaf stem separate from each other, causing the leaves to drop. But in marcescence, this does not occur until spring.

Trees create a separation zone (abscission layer) between the leaf stems and branches. If the separation layer is complete, the leaves will drop to the ground, adding nutrients to the soil as they decompose. Trees shed their leaves to prepare for winter by conserving water and food made through photosynthesis. Marcescent trees do not form this abscission layer completely and so the leaves hang on through the winter. Younger oaks may keep what looks like a full covering of dead brown leaves, while more mature oaks keep them on just the lower branches.

Scientists do not know exactly why this happens but there are theories: the leaves add nutrients to the soil for growth in the spring and form a layer of protection from snow and ice. By remaining attached the leaves offer a protective barrier over the buds that are forming underneath.

When new growth begins in spring, the expanding buds will push the old leaves off and the branches will have new green leaves.

There are interesting theories involving wildlife. The dried leaves may provide a certain amount of shelter from winter winds for birds, and squirrels. It may also be a defense mechanism against browsers. It is possible that the dry, un-tasty leaves discourage browsing from deer, elk, and moose. Deer have a 7-foot reach, elk have a 9-foot reach and moose have a 14-foot reach. It is interesting that the average height for the dead leaves is around 20 feet, far beyond the reach of any modern browsing mammal.

Browsing mammals that roamed the earth 10,000-15,000 years had a maximum reach of about 20 feet. So, one theory is that this is why the typical height of marcescence occurs at 20 feet or more. Giant Ground sloths were larger than modern-day elephants, standing thirteen feet tall with an even higher reach by extending their forelegs to forage. Mastodons stood 8 feet tall at the shoulder and could reach another 5 feet with their trunks. I think that is remarkable that the trees adapted to the heights of various browsers.

While there are theories as to why marcescence exists, I like it that we do not have all the answers to nature’s mysteries.

As I wander in the winter with my camera I stop to admire the contrast between the beautiful beige leaves, the snow, and the blue skies.

I also like to listen to the rattle they create when the wind blows. Call me weird, but I like that sound!

Jeannie Carl is a naturalist at the Carbon County Environmental Education Center in Summit Hill. The center rehabilitates injured animals and educates the public on a variety of wildlife found in the area. For information on the Carbon County Environmental Center, visit www.carboneec.org.