Just looking around my yard today, realized one of the oak trees is rather odd imo. The bottom 1/3 of the tree still hasn't dropped its leaves, while others have and the rest of the 2/3 has dropped. I'm wondering if this s a type of auxin related inhibition/prohibition or related to something else. Is it specific to genus Quercus? I'm into botany chem., phytochem. and such, just wondering. I never notice any other trees that don't drop leaves all at once. Thanks. The picture shows the tree, leaves bottom, not top half. I'm not worried about the tree itself, just about this leave question. Sorry for not that great of a picture, took it from inside through a window.
Oak and Beech commonly hold their leaves well in to winter, I am not sure of the chemical reasons off the top of my head, the process is leaf senescence (defined as: Senescence - death of a leaf triggered by an increase in the enzymes that promote the breakdown of plant cells. Begins when shorter days and cooler temperatures occur. )
Do you know the species? Are the lobes pointed or round? I was surprised to drive through Gasquet, California, returning from the redwood forest the other day, and see about 1/2 the leaves still remaining on the sweetgum trees there.
Some sweetgums here have almost no fall color, behave as though trying to be fully evergreen. "Its maple-like, star-shaped leaves...sometimes persist, enduring green even into the New Year...It shows MUCH variation in...fall color and leaf retention." --Jacobson, TREES OF SEATTLE - SECOND EDITION
Oaks (and beeches and hornbeams) often retain dead leaves through the winter on low branches (and also throughout on young trees up to 2-4m tall). Various suggestions have been made why this might have evolved, the most commonly cited is to give the buds some protection from either severe cold (cold air collecting at ground level), or else from browsing animals. Whether these are correct or not, hard to know.
