A natural chain of events start in late August that culminates in October with the beautiful colors of autumn and leaf fall. Controlled aging of specific cells in plants, the process called senescence, prepares every tree for dormancy and ends in leaf fall. The very last event in the process of senescence is caused by a sealing of the leaf attachment and called abscission.
Fall foliage color change and leaf shed is the direct result of a leaf's abscission. Fall leaves abscise due to the reduction of chlorophyl when the hours of sunlight shorten. The connective cell layer (the abscission zone) where leaf connects to twig begins to harden and blocks the transport of nutrients between the tree and leaf. This final biological event creates the majestic colors and forest views of the fall season.