The science of fall foliage: Why do leaves change color?

Average peak fall foliage across the Lower 48
Average peak fall foliage across the Lower 48(WOWT)
Published: Oct. 7, 2020 at 1:54 PM CDT
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OMAHA, Neb. (WOWT) - Leaves have color due to chemicals – or pigments. During the spring and summer, trees are green because they are producing high amounts of chlorophyll through the process of photosynthesis.

Why do leaves change colors in the fall?

As we transition into fall, the daylight hours become shorter and shorter, and trees begin to transition as well. With less sunlight, less chlorophyll is produced, allowing the other pigments to take center stage. These other pigments produce the yellow, orange, and red leaves we love to see in autumn.

Why do leaves change color?
Why do leaves change color?(WOWT)

How does the weather impact fall foliage?

Weather can impact when leaves change colors, how vibrant the colors are, and how long the fall colors last. For example, lack of soil moisture can delay the onset of color during autumn. An early frost can also cause leaves to fall off the trees before they’ve changed colors.

Drought can impact fall foliage in a number of ways, depending on the extent of drought and the species of trees. A severe drought can cause an early turn of leaves, as the trees are stressed. The color tends to not last as long, with some trees browning and leaves falling quickly.

Moderate to severe drought persists
Moderate to severe drought persists(WOWT)

More moderate drought may delay the onset of color by a week or two, due to the slowing of metabolic processes. Different species of trees handle stress and drought differently, as well.

The best conditions for beautiful fall leaves include warm autumn days, cool nights, and plentiful sunshine. This allows an abundance of sugars to be created during the day, to then be trapped in the leaf at night. Moisture during the growing season, followed by a dry late summer/early fall can enhance colors as well.

Peak fall foliage in eastern Nebraska spans from mid to late October; western Iowa peaks slightly earlier. A great interactive map regarding fall foliage can be found on the Smoky Mountain website:

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