In autumn, deciduous trees will shed their leaves. This process is known as leaf abscission. Curiously, out at the arboretum, there are a few oak trees that still have the copper-brown leaves from last autumn. Why aren’t the leaves falling off the tree?
The process of holding onto to the leaves through the winter is known as foliar marcescence. From what I have read, this phenomenon is seen in trees like oaks, American beech, hornbeams, and witchhazels.
How this happens is understood—the leaf hasn’t formed an abscission layer at the base of the leaf petiole allowing the leaf detach. Why this happens is a bit of a mystery. The leading theory is that the dead leaves are not palatable or nutritious so they protect the leaf buds from browsing mammals, like the black-tailed deer that live at the arboretum. In addition, rummaging around dry, noisy leaves could potentially alert nearby predators. Another theory is that delaying the leaf drop until spring provides a fresh layer of leaf mulch around the base of the tree.
Leaf marcescence is usually seen on small, younger trees or on the bottom limbs of mature trees. I found examples of both occurrences at the arboretum. Another interesting part of this story, which I have yet to read about, is that I saw leaves on the tree that were older than last year. There were layers of gray, decaying leaves on the limbs, and some had a substantial amount of lichen growing on them. Those have to be leaves from at least the year before last.
There are so many mysteries in the world, even in our own backyards.
Resources
Feb 13, 2019 | Print. “Winter Leaf Marcescence.” Home & Garden Information Center | Clemson University, South Carolina, https://hgic.clemson.edu/winter-leaf-marcescence/. Accessed 11 Mar. 2023.
“The Mystery of Marcescence.” Tennessee State Parks, https://tnstateparks.com/blog/the-mystery-of-marcescence. Accessed 11 Mar. 2023.
