On 17 Nov 2016 we reached a near-record high of 75˚F in eastern Iowa. It started to cool off the next day and got very windy. That night and the next day were much colder and windy with gusts in excess of 45 mph. Most of the trees already dropped their leaves before this recent weather. The strong wind removed the rest, except for the mulberry trees. They still held tight to their dried leaves.
The next morning, it was the coldest night of the year at 20˚F. We knew what to expect from the mulberry trees. As the temperature warmed to near freezing, they would drop their remaining leaves within an hour. The process involves something called abscission. Earlier colder and frosty nights triggered the formation of a thin layer of cells at the base of the leaf stem. The very cold temperature helped complete the process of cutting the leaf loose from the stem so it could fall.
In this video the leaf drop occurs on the tree behind out neighbor as the sun warmed the leaves. There was no wind. The video is speeded up by 4X. It will help to view on a larger screen.
Our View From Iowa 