You go for a long walk in the woods on a quiet winter day. All you hear is the crunching of snow as your boots hit the trail. The breeze picks up. And then you hear it. It starts out as a rustle, grows to low a rattle, and then, suddenly, it’s a crackling cacophony.
It’s wind blowing through the leaves—but it’s winter, right? And shouldn’t the leaves on the trees be gone by now? Yet, there they are—brown leaves hanging onto the branches. It may not make sense to you, but it can be normal for some trees, and it’s called “marcescence.”
Photography by Joy Yagid.
What is marcescence?
Marcescence is when deciduous trees hold on to most of their dead leaves until spring. Only certain trees do this, mainly beeches and oaks, but also hornbeams and witch hazels and, sometimes, Japanese maples. The leaves may turn color in the fall, but they won’t fall off. Instead, they persist, wrinkled and brown, until new growth finally pushes them off the branches.
What causes marcescence?
We are used to seeing bare trees in the winter in the northern part of the country, where deciduous trees lose their leaves in the fall. Some, like sugar maples, put on a colorful show before they go. The process for how trees lose their leaves is called abscission. Hormones in the tree, activated by the dwindling length of daylight, are prompted to start cutting off nutrients to the leaves; by mid-autumn, they start to fall. However in marcescence, the tree cuts off nutrients but the leaves do not separate from the tree. They remain on the tree until spring.
Why does marcescence happen?
No one knows for sure, but scientists have a few guesses. First, it may be to protect next year’s leaf buds from being nibbled on—younger trees and the lower branches of older trees are more likely to experience marcescence. Food for forest animals tends to be scarce in the winter. Deer will nibble on just about anything. Keeping the dead leaves on the tree is thought to protect the tender buds from being eaten. Second, marcescence may occur when there’s a need to for moisture. The withered leaves can both collect dew and direct rain to fall down within the drip line of the tree’s feeder roots. Even though it’s winter, the tree is still alive and still needs water. Third, once the leaves finally fall in the spring, they can form a layer of mulch that will lock in the moisture around the feeder roots and eventually provide the perfect closed loop fertilizer. They are exactly what the tree needs, since it came from the tree.
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