Why do leaves change color?
The changing colors of leaves is a way for the leaf and tree to prepare for winter. Leaves appear green because of the chemical chlorophyll that is contained in chloroplasts Leaves change color because chlorophyll is destroyed and not replenished by the tree
WHY? Less sunlight = longer nights Cooler temperatures
How does the Chlorophyll Fall Apart? Abscission zone forms Cork like structure at the base of the petiole Block the flow of water and glucose into the leaf and trap the toxins in. Chlorophyll can no longer regenerate and the color green fades Abscission zone
What is Left Behind? Carotenoids Orange color Red maple, Sassafras, Willow Present year round but color is hidden by the chlorophyll
What is Left Behind? Xanthophylls Yellow color Ash, Aspen, Birch, Beech, Maple Present year round but is hidden by the chlorophyll
What about Red? Anthocyanins Red, purple, crimson color Box elder, Cherry, Maple, Dogwood Anthocyanins are not present year round, they are produced as the chlorophyll is degenerating The glucose trapped by the abscission zone is used to create the red pigment The formation of the red color is dependant upon warm and sunny days but cold nights
Why do leaves turn Brown? The flow of nutrients has been cut off by the abscission zone Toxins fill the leaf Tannin-waste product from pigments Tannins have a brown color Once the leaf is brown, it is dead No photosynthesis is taking place
Why do the leaves fall off the tree? They are dead Protection for the tree Dead leaves freeze easily and if the leaf freezes the branch might also Abscission zone is the weak point so leaf breaks off at the abscission zone
Why do coniferous trees keep their needles? The cuticle on the needle is a thick waxy covering which prevents the needle from freezing or losing too much water.