Oak Trees- why won't the leaves fall?

[bewildered_nmsu]

It's funny that you mention that on the pine trees. Just the other day I noticed that my neighbors Italian stone pine retains it's upper cones through the winter, while dropping its lower cones in the Fall. Perhaps to ensure that there are fresh seeds stratifying on the ground in Fall and Spring?

[plants4us]

For reasons that are unclear, some species of oak trees do not lose their leaves over winter. Leaves detach (senesce) in the fall because of the formation of an abscission zone where an abscission layer (separation layer) forms at the base of the petiole (leaf stem). The process is usually associated with a decline in auxin "hormone" levels. Peptic acid in the cells of the abscission layer convert to pectin resulting in weakening of the zone via cell death and formation of a callus. Abscisic acid may also promote "senescence" of the leaf. In the case of the oak trees, it is believed that the cells of the abscission layer do not completely die so the leaves remain attached until the following spring when new growth begins.