Our “December in October” weather this fall was not welcomed by many of us, including the deciduous trees that were showing fall color or still green and growing. The extreme early cold temperatures, well below 32 degrees, killed many of the green leaves and now we see them still hanging on the trees. These dead leaves are referred to as marcescent leaves. We do not expect to see this every year, but it has been more common in the past few years.
Some trees — oak and beech especially — have marcescent leaves every year and many people speculate if this persistent foliage may help trees and enable them to adapt to environmental conditions.
In a normal year, trees form a layer of corky tissue, an abscission layer that stops the flow of water and sugars in and out of the leaves. After the layer forms, the leaves drop. This year, extreme cold (20 degrees below normal) killed the leaves before they could form this layer and the leaves literally froze on the branches.
Many leaves will stay on until next spring, others may fall off later this winter. It’s a normal phenomenon and one we may see more of in the future.
Read Why Do Some Leaves Persist On Beech And Oak Trees Well Into Winter? to understand how this may actually help the tree.