Why Do Leaves Turn in the Fall & Look Yellow & Orange?

In some areas of the world, fall brings changes to deciduous trees. The foliage changes from shades of green to vibrant reds, oranges and yellows, though these bright leaves eventually drop from the tree and fall to the ground. The changing leaf colors of fall is caused by a scientific process that begins on the cellular level.

Certain pigments are present in some types of leaves, which is what gives foliage its fall color when it changes in the fall. All leaves contain chlorophyll, the pigment that turns foliage green. Chlorophyll is essential for photosynthesis, the process by which plants gather and store energy from the sun. Carotenoid pigments create yellow, orange and brown colors in leaves; the pigment also is present in yellow flowers like buttercups, roses and tulips. Anthocyanins, which create red colors, are not always present in leaves like chlorophyll and carotenoid. Anthocyanin pigments are created as a response to bright light and excess plant sugars in leaf cells.

Leaves constantly produce chlorophyll during the spring and summer growing season, but production slows down when fall arrives and the nights grow longer. Eventually, chlorophyll production halts entirely, giving carotenoids and anthocyanins the opportunity to shine. Once the green-creating chlorophyll is out of the way, the leaves change colors because other pigments begin to show through. The absence of chlorophyll and the color change in leaves actually indicates that the leaves are dying as the tree prepares to go dormant through the winter.

Some trees are known for changing specific colors during the fall. The leaves of oaks turn red and brown. Hickory trees, aspens and yellow poplars turn yellow when fall arrives. Red maples, as the name suggests, produce vivid red leaves, while the black maple presents bright yellow leaves in fall. Some trees also wait longer than others to change leaf color. Oak leaves, for instance, change colors long after other trees have shed their leaves.

Weather conditions play a large role in changing the colors of leaves, and certain weather conditions may affect the shading and brightness of those colors. Regions that experience a consecutive series of warm, sunny days followed by cool nights (above freezing) in the fall will enjoy vivid, spectacular color change with lots of bright, deep reds and yellows. Summer drought may delay the color change of leaves in the fall, and an unexpected period of warmth in fall will dull the leaf colors. Warm, wet springs help create bolder, brighter color displays.