When leaves fall change color, it’s carotenoids, anthocyanins at work
Though the green of chlorophyll is what you see during the growing season, there are hidden colors in the leaves, called carotenoids. They’re the same pigments that make carrots orange and corn and daffodils yellow.
In fall, shorter days and cooler nights mean there’s less energy for food-making, so chlorophyll starts to break down. Yellow carotenoids can finally be seen in such trees as hickory, ash, birch, maple, sycamore, cottonwood, and sassafras. Red and purple colors in the leaves are newly created in fall when sugars are made during warm days are trapped in the leaves during cool nights. Trapped sugars change chemically into anthocyanins, which appear red and purple.
The more sunshine during the day, the more red color is created. That’s why shaded leaves will be less red than those that get lots of sun. If the weather is cloudy and the nights stay warm, there won’t be as much vivid red in such trees as maple, sweet gum, oak, and dogwood.
Other factors besides contrasting temperatures also affect fall color. Trees that don’t get enough water during the growing season may drop their leaves quickly before they color. And if it gets very cold, that kills the leaves too early for a fall display.
In good seasons, the Ozarks’ fall color may slowly change in mid-October. In a few weeks, the colors fade and the incredible show is gone.