A birch tree displaying marcescence. Photo credit: Andrew Birch
Have you noticed that some of Rock Creek’s deciduous trees, those that are supposed to drop their leaves in the winter, are still hanging on to brown, shriveled bundles?
This phenomenon is called marcescence, and it might be the key to some trees’ survival.
Making sense of marcescence
Marcescence occurs when plants hold on to dead plant material throughout the winter rather than discarding it. Typically it only occurs on a few branches per tree, leaving the winter landscape speckled with leftover hints of the autumn’s orange-brown hue. This phenomenon is seen commonly on oak and beech trees throughout the Rock Creek watershed.
This oak tree isn't letting go. (Not until spring, at least.) Photo credit: Paul Morris
We may be seeing more marcescence on oaks this winter. Dr. Jessica Sanders, the Director of Research and Development at Casey Trees says, “A lot of oaks have held onto their leaves due to the second flush they had last fall.” The second flush refers to a warm snap that happened late last fall which encouraged growth of more leaves later in the season.
Holding on to dead weight or smart adaptation?
Why are these trees so unwilling to shed last years leaves, bare their branches, and enjoy some freedom for the winter months? Here are three theories:
A full set of leaves in January? This oak tree is a showing Marcescence in action. Photo credit: James Mann
1. Playing defense
One theory suggests these plants do it as a defense mechanism against deer. Trees will keep deer away from fresh twigs and delicious buds by distracting them with these dead leaves. It’s kind of like junk food for the deer, these leaves are less nutritious but plentiful.
Is marcescence a deciduous defense against deer or a nutritious springtime energy drink?
2. Spring mulch
Another theory suggests trees save these leaves to use as nutrients in the spring. The trees are essentially creating their own personal mulch by dropping leaves, which turn into nutritious, organic matter when they need it most. This is believed to be especially true for oaks and beeches that are planted on infertile sites.
3. Staying hydrated
Lastly, it is believed some trees hold on to dead leaves to create more surface area that can capture snowfall over the winter. Once the snow melts, it can be used as a much-needed water source for the tree.
In reality, each tree is different, and they hold on to their leaves as a way to adapt to their unique microclimate.
Regardless, it’s important to realize that even though it’s winter, and the woods seem dormant, there is so much to explore! It’s a matter of getting outside and investigating the complexity of our natural world.
Svendsen, Claus R. 2001. Effects of marcescent leaves on winter browsing by large herbivores in northern temperate deciduous forests. Alces 37(2): 475-482.
Woodlands, Northern. "Why Do Some Leaves Persist On Beech and Oak Trees Well Into Winter? | Winter 2010". Center for Northern Woodlands Education. Retrieved 2017-11-16.
Author: Arielle Conti - Program Manager - Rock Creek Conservation Corps