The colour show that we experience here in the north-east is stimulated by both shorter days and cooler temperatures. The dominant pigment in leaves is chlorophyll, which keeps them green throughout the growing season. But chlorophyll is unstable and weakens under less than optimum conditions, namely cold temperatures and decreased sunlight. This is when other pigments, anthocyanins, tannins and carotenoids, take centre stage; first in barberry (Berberis thunbergii) and then in chokeberry (Aronia arbutifolia):
An abcission layer of cells begins to form at the petiole end of each leaf connecting it to the branch. This finally results in leaves losing their grip and falling to the ground.