The Little Leaves That Could
The recent, very windy days left many trees down in the High Country.
It will be interesting to watch as these trees enter a new stage of their lives: the rotting log. They will become shelter, food and fertilizer.
The wind served as a reminder as to one of the reasons why deciduous trees lose their leaves in the fall. If the trees still had their leaves, green and broad, such strong wind would have caused considerably more damage.
These hypothetical green winter leaves would catch the gusts like little kites. Perhaps more trees would have lost limbs or fallen over altogether.
Deciduous trees also lose their leaves to reduce water loss and frost damage during the coldest months.
But not all broad-leafed trees are altogether deciduous. One hike through the wintery woods and you will discover that some leaves are holding on tight.
Today’s question focuses on two types of trees that have not yet fully followed in their deciduous cousins’ adaptive footprints.
Why do beech and oak trees hang on to their dead leaves during the winter? – Anne H., Boone
The first trees on the planet were evergreens. These trees, like our pines and hemlocks, hung on to their needle-like leaves even during the winter. Though even these trees would shed their leaves as they aged.
As trees evolved, they adapted new ways to grow and shed leaves. These new leaves were broad and better at photosynthesis, but would have to go for the tree to survive winter. Thus, our hardwoods were born.
There is a family of tree, however, that does not fit into the evergreen and deciduous stereotypes.
Beech and oak trees are actually members of the same family: Fagaceae. Some species in this family, like live oaks, are actually still evergreens. But most seem to be stuck in evolutionary limbo. Their leaves die in autumn, but do not fall to the ground.
This retention of dead leaves is called marcescence.
Take a closer look at the beech and oak trees, Anne. You will notice that the marcescent foliage is only found on young trees or the lower branches of older trees. This is important.
You see, there are several hypotheses on the possible ecological advantages of marcescence.
One such hypothesis is that the dead leaves hide emerging, spring buds from browsing deer. These buds have less of a chance of being eaten, and thus will live to become new leaves.
Another study suggests that marcescence allows beech and oak trees to grow in places that are too dry and infertile for other trees.
Their winter leaves trap snow, leading to more moisture at the base for the spring. Dropping them in the spring also delivers important fertilizer to the tree’s roots right when it is needed most.
If you have a question concerning flora and fauna, please email (firstname.lastname@example.org) All of your questions will be answered. One will be featured next week. See you on the trails!
Amy Renfranz is an interpretive park guide on the Blue Ridge Parkway. She is a certified naturalist through the Yellowstone Institute and a certified environmental educator in the state of North Carolina. Her comments are made independently and do not reflect the views of the National Park Service.