Why do leaves change color in the fall

There is a tree across the street that has the most beautiful fall coloring every year. Is it the weather, the species, the soil; what makes trees change into a specific color in the fall?

It turns out that there are a lot of factors that determine the color of an autumn leaf. As days shorten and temperatures become crisp, the common green summer foliage is transformed into a vivid red, orange, yellow, or brown before it drops.

Three factors influence autumn leaf color: length of night, leaf pigments, and weather. As days grow shorter, and nights grow longer and cooler, biochemical processes in the leaf begin.

The leaf pigments involved in color change include chlorophyll and carotenoids which are present in the leaf cells throughout the growing season and anthocyanins which are produced mainly in the autumn.

During the growing season, chlorophyll is being produced continually and broken down to produce green leaves. As the days shorten in the fall, chlorophyll production slows down and then stops. That’s when the carotenoids and anthocyanins show their colors.

Certain colors are characteristic of particular species. Oaks turn red, or brown; hickories turn golden brown; aspen and yellow-poplar turn yellow; dogwoods turn purplish red; and beech a light tan. Maples differ species by species: red maples turn brilliant scarlet; sugar maples turn orange-red; and black maples are bright yellow.

How bright the colors are is determined by the temperature and moisture. A succession of warm, sunny days and cool, crisp but not freezing nights seems to bring about the most spectacular color displays.

During these days, lots of sugars are produced in the leaf and the cool nights result in a gradual closing of veins which prevents the sugars from moving out. When there is a lot of sugar and a lot of light, the brilliant reds, purples, and crimson develop. Because carotenoids are always present in leaves, the yellow and gold colors remain fairly constant from year to year.

The amount of moisture in the soil also affects autumn colors. A warm wet spring, favorable summer weather, and warm sunny fall days with cool nights should produce the most brilliant autumn colors.

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