When visiting our site I was overwhelmed with disappointment when I saw that the leaves on the trees there were not those hot, colorful red and orange hues that I had seen on trees in Connecticut the previous weekend. When I think of fall, I think of the cooling days, the smell in the air and very red leaves all over the place, on the trees and falling to make a stunning red carpet on the ground. Fort Greene Park was lacking those magical colors- all I saw were various stages of green, yellow, and brown. Very predictable considering the loss of chlorophyll would explain the loss of color to reveal the yellow that had been there all along, but what about the red leaves, or those deep burgundy leaves, or the ones that are firey reddish orange? How do those exist?.
That gorgeous red occurs when the leaf is hanging there in its final days, ready to drop and turn brown. Is this because of the cold weather? Is this a protective device to help the old leaf live just a little bit longer? Is the leave conserving energy by being red? Why red? The colors of autumn leaves are mostly caused by the loss of chlorophyll, the chemical that makes leaves green and that is produced in the warm spring and summer seasons. This really doesn't explain the red, though. There are many theories about the origin of red leaves. The most in depth exploration is of a resurrected 19th century notion that the red pigments are anthocyanins and their purpose is that of a protective device when photosynthetic chemistry is failing. Anthocyanins are found not only in autumn leaves but also in hot-weather plants with red leaves. The anthocyanins are associated with young, old, or sick plants. They are thought to screen ultraviolet light. The anthocyanins color fall leaves because the leaves are old and need protection from the sun and other stresses.
There is a question of the amount and type of light that a plant is subjected to and how light affects the chemicals of chlorophyll and those of anthocyanins.