Why the Oak Trees Keep Their Leaves

Ever wonder why some deciduous trees hold onto their leaves throughout the winter? I have noticed especially young oaks and the lower branches of older oaks laden with brown winter leaves.

Among many of the theories in circulation, here is one that could hold a bit of validity. Noting that wind will better catch and remove the higher placed leaves, and easily blow them away while the lower leaves are retained, suggests that the resultant minimal leaf litter below the tree might help keep the acorns from being covered before animals have a chance to disperse them. (I have a problem with this theory, such as what happens in the woods? Lots of leaves lay thick on the ground regardless of how hard the wind blows.)

The first picture is of a young red oak, not over 20 feet tall. The other two pictures are of a different tree, an older specimen, showing how the lower branches retained leaves but higher up the tree is bare.

Science explains how some leaves tenaciously hold, but not exactly why. A few tree species do not complete the development of their abscission layer until the spring, meaning that the petiole base remains alive through the winter, such as with the pin oak. Typically, abscission cells are formed in the fall, and kill the leaves by cutting off water flow, then the cells die and the leaf falls off.


But the oaks in my pictures instead retain dead plant organs, a process known as marcescence. Other trees in our area that also have marcescent leaves are hornbeams and beeches. In these trees the abscission cells form, but remain along with the old leaf until the new spring leaf's emergence causes them to sever and fall away.
Since both young trees and new branches attract browsers such as deer, it is speculated that by maintaining old, bitter tasting leaves, there is less chance of the new branches and buds being eaten. In some marcescent tree species, the old leaves may as well help protect from water or temperature stresses.

And finally for one more theory:

http://www.rosannebane.com/pdf/Why%20Oak%20Trees.pdf