Autumn is the time when leaves fall from the trees. It may seem like a gradual process but often, leaf loss can be sudden; especially after an overnight frost or during gale force winds.
As summer winds down, deciduous trees produce cells at the base of each leaf stem called the abscission layer. This layer weakens the attachment of the leaf to its tree while blocking nutrients from nourishing the leaf causing its chlorophyll to degrade. Since chlorophyll is green, other colours such as red or yellow can then become more prominent.
Frost can accelerate the process by further weakening the abscission layer so that leaves are very loosely attached and will fall at a slight breeze. Early frosts are the enemy of glorious fall colours as they can send leaves to the ground before colours can develop.
This video was taken in Raymore Park on the morning of November 12, 2013 and illustrates how quickly leaves can fall from trees when conditions are right. There had been an overnight temperature of -4°C the night before, severely weakening abscission layers and even the gentlest breeze was enough to send large numbers of leaves to the ground.