Recent cooler days have given the signal to deciduous trees that the time has come: They must discard their many jewels now and become inconspicuous as the potentially ravaging winter approaches looking for victims. I suspect that, by next weekend, most of our deciduous trees will have become gray and will have faded into the backgrounds of our awareness.
More specifically, as I understand the process, cooler temperatures and shorter days reduce the trees’ production of the hormone auxcin. This weakens spring’s bonding layers of cells that join the leaves to the branches (the “abscission layers”). In a short time, the depleted joint for the leaf stem is too weak to withstand blowing wind or rain and the leaves take their only and final flights to the ground.
The fall process of leaf coloration and liberation apparently is a defensive survival measure: Winter’s cold and sometimes severe winds can now blow through the trees’ branches with far less strain on those limbs; moisture is conserved within the trunk to prevent its drying out and weakening, and energy that was needed to keep leaves alive is saved.
(Images taken in Brooklin, Maine, on October 24 and 25, 2024.)