You can thank the dwindling daylight for autumn’s festive garb.
The reds and yellows are mainly a reaction to the days getting shorter, said Dennis Adams, a forester with the University of Nebraska-Lincoln Extension, in a UNL article on the phenomenon.
As daylight decreases, so does the amount of chlorophyll produced by trees. Chlorophyll is a green pigment necessary for photosynthesis, or how plants absorb energy from light. It’s also not the only pigment in trees — trees can also contain carotene (orange), xanthophyll (yellow) and anthocyanins (reds and purples).
In the summer, chlorophyll is readily replaced as it’s broken down and nutrients are sent to the trunk; in the fall, not so much. When that happens, only yellow pigment remains in the leaves, giving us those familiar colors. It’s also why the leaves die and fall off the tree.
Most often, we’ll see yellow and orange, carotene and xanthophyll.
As for the brilliant reds and purples, they’re often a result of a tree having more food than it can store, which causes a reaction with excess sugar to create anthocyanins, according to Adams.