Naturalist Notes: Should I Stay or Should I Go?

Beech tree leaves in winter (photo from University of Maryland Extension)

Now, I know what you are thinking: 'A third article in a row about leaves?' or 'What else is there to know about leaves?'

Well, we’ve learned how and why leaves change colors, and what to do with the leaves when they fall, but we haven’t talked about the leaves that cling to some trees throughout the winter.

Have you ever noticed the brown, crunchy leaves on oaks and beeches in the middle of winter and wondered why they didn’t drop with the rest in autumn? There is actually a word for this: marcescence, pronounced 'mar-SESS-sense.'

No one is really clear why some trees keep their brown leaves, but there are a lot of theories. Some think it is an adaptation to protect the buds from being browsed by deer. The leaves might help hide the buds, and their rustling might scare the deer away.

Another theory suggests that keeping the leaves throughout the winter and letting them drop in the spring will give these trees a jolt of nutrients when they start to grow for the season. When a leaf drops, it starts to decompose almost right away, returning nutrients to the soil. Now, most leaves that drop in autumn either get removed by people or blown around by the wind. If the leaves drop in the spring, there is a great chance of them decomposing right under the tree, giving back some key nutrients.

Not only do the leaves give the tree nutrients, but they might also provide the tree with a nice, long drink. The leaves will catch more snow through the winter, which will then drop in larger piles right under the tree. When the weather warms up and the snow melts, oaks and beeches have more water around them for their roots to soak up.

All of these reasons make a lot of sense when you consider where oaks and beeches grow, mostly in dry, infertile sites. Why do you think some trees hold onto their leaves?

Submitted by naturalist Cathy Wesley, December 2023