What is the advantage for the oak trees in the Northeast to hold their leaves in the fall?

Answer 1

First, some background information: In oak trees, the "separation layer" that forms at the base of leaf stems in most broadleaf trees in autumn, does not form completely.

From the website, "Why Leaves Change Color":

"A tree's roots, branches and twigs can endure freezing temperatures, but most leaves are not so tough. On a broadleaf tree -- say a maple or a birch -- the tender thin leaves, made up of cells filled with water sap, will freeze in winter. Any plant tissue unable to live through the winter must be sealed off and shed to ensure the tree's survival."

"As sunlight decreases in autumn, the veins that carry sap into and out of a leaf gradually close. A layer of cells, called the separation layer, forms at the base of the leaf stem. When this layer is complete, the leaf is separated from the tissue that connected it to the branch, and it falls. Oak leaves are the exception. The separation layer never fully detaches the dead oak leaves, and they remain on the tree through winter."

(http://dnr.wi.gov/org/caer/ce/eek/veg/trees/treestruecolor.htm)

Something about the Scarlet Oak:

"Scarlet oak provides a special bonus for our autumn enjoyment. Its leaves stay attached to the tree into the winter. Normally, leaves of deciduous trees are shed in the fall after a special layer of cells forms at the base of the petiole (the abscission zone). With a little wind, these thin cells break and the leaf falls. In so-called marcescent (leaves withering but not falling off) species, including many oaks and beech, the abscission zone doesn’t begin to form until winter, and the leaves are not shed until winter or spring. One writer speculates that the pilgrims landing at Plymouth Rock must have appreciated scarlet oak as the only tree in the forest that still had leaves. While the veracity of this story seems tenuous, the idea that scarlet oak is a species to enjoy is solid as an oak."

(http://www.discoveret.org/utarboretum/falltreearticle1.htm)

The big question is: Why do the oaks do this? (Called "marcescence.") What advantage would they have in keeping dried, dead leaves on for such a long period of time?

From Wikipedia:

"Marcescence is considered a juvenile characteristic because it is more common on younger trees and on the lower, more juvenile, parts of older trees. One possible advantage of marcescent leaves is that may deter feeding of large herbivores, such as deer and moose, which normally eat the twigs and their nutritious buds. Dead, dry leaves make the twigs less nutritious and less palatable."

"Marcescent leaves may protect some species from water stress or temperatures stress. In Espeletia schultzii, an evergreen rosette species living high in the Andes, removal of marcescent leaves increased the probability of the plant dying. In Espeletia timotensis marcescent leaves improved plant water balance and protected the plant from cold injury."

(http://en.wikipedia.org/wiki/Marcescence)

I suspect too, that when the leaves do fall in late winter, they have an insulating effect on the snow already on the ground -- allowing for it to stay in place much longer than if the leaves were under the snow.

Answer 2

Oak trees retaining their leaves in the fall provides no distinct advantages for the trees. The reason deciduous trees lose their leaves in fall is they are no longer needed for photosynthesis since it will become dormant. It sort of like what advantage would a person have by not throwing out the Sunday paper they've read in its entirety. No distinct advantage.

Answer 3

I wonder if is it an advantage or just a genetic proprieties.
Could be that they are thicker and are not affected by frost as quickly

But for sure, keeping leaves longer gives the possibility of doing photosynthesis longer.

If they stay all winter and are used again next year, than its an energetic cost that is saved.

Answer 4

to protect the buds and possibly to help hide the acorns from predators