Why do some trees keep their leaves during the winter?

Trees such as Beech, Hornbeam and Oak keep there leaves all winter long. Why is that? It is a process called Marcescence. Marcescence is the retention of dead plant matter that is usually shed. Deciduous trees or trees with large flat leaves use their leaves in the spring and summer to create "food" or energy using a process called photosynthesis. During this process trees use carbon dioxide, water and light energy to create carbohydrates (sugar) and oxygen. During the winter when trees are dormant this process is not active. So to help stop the loss of water they will shed their leaves and seal off the opening where they were once attached (there are a lot of technical terms involved with that process but we will get into that another time).

So why keep the leaves?

We don't really know for sure! There are several theories that could make sense. Generally most trees that are found in the forest setting that have keep their leaves are juvenile. So one theory is that the rustling of the leaves helps to deter deer and other foraging animals from feeding on the new buds and live tissue. Another suggestion is that because most trees lose their leaves in the fall most of the nutrients are used up when spring arrives. So to keep all that goodness to themselves and give a boost in the spring when the nutrients are needed the most, young trees hang on to the leaves for just the right time. Trees are so neat! It has also been noted that when we get really quick cold snaps in the fall some trees retain their leaves, because they do not get the opportunity to close off the vessels properly.

So what ever the reason, next time you are walking in the woods, take notice of those beautiful understory trees decorated with brown crispy leaves. There is so much more going on there than we realize.