1. Why do leaves change color?

2. 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

3. WHY?
Less sunlight = longer nights
Cooler temperatures

4. 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

5. What is Left Behind? Carotenoids Orange color
Red maple, Sassafras, Willow
Present year round but color is hidden by the chlorophyll

6. What is Left Behind? Xanthophylls Yellow color
Ash, Aspen, Birch, Beech, Maple
Present year round but is hidden by the chlorophyll

7. 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

8. 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

9. 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

10. 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.