Take a walk in a winter forest and you can’t help but notice beech trees. Silky smooth bark and sand-colored dry leaves stick out like Christmas lights against a dull and gloomy background. While every other leaf drifted to the forest floor months ago, beech leaves hold tight like cat hair on a sweater.
It’s called marcescence – these leaves that just won’t drop – and it’s common in oak and beech (the trees are close relatives). But why keep the leaves? Are these trees just photosynthetic versions of hoarders?
One possible reason may be to protect that bud, the thin tapered structure often described as “cigar-shaped.” Inside the scaly covering are the beginnings of the new year’s growth. Hungry deer can ruin a tree’s plans for spring. But with beech trees, deer tend to get a mouthful of dry leaves whenever aiming for a yummy bud. (1)
What about attacks from smaller enemies? Insects seem to prefer infesting trees with leaves hanging on over winter. R. Karban decided to yank all the leaves off a few dozen small oaks and compare infestation levels of a tree-noshing wasp. (2) His numbers indicate that wasps prefer leaf-hoarding trees three-to-one compared to his denuded ones.
I believe Nature is constantly sending messages of wisdom if we’ll just listen. In this case, perhaps she’s saying “every action has an upside and downside, but with diversity, there’s always hope for a better future.”
- Svendsen, Claus R. 2001. Effects of marcescent leaves on winter browsing by large herbivores in northern temperate deciduous forests. Alces 37(2): 475-482.
- Karban, R. 2007. Deciduous leaf drop reduces insect herbivory. Oecologia. 153: 81-88.