Leaves Turning Ahead of Schedule, UA Forestry Professor Says

FAYETTEVILLE, Ark. — Cool temperatures in September have produced some early fall color in Northwest Arkansas, but the trees still have some time to become showy, if the weather holds steady, according to Laurin Wheeler, associate professor of forest ecology at the University of Arkansas.

Shorter days, light rains and cool temperatures send signals to the trees, which stop producing chlorophyll, the green pigment in leaves. When chlorophyll production ceases, the yellow and red colors previously masked beneath the green show through, creating colorful displays.

Leaf color usually peaks in Northwest Arkansas during the last week of October or the first week in November, Wheeler said.

Tree color varies throughout Arkansas depending upon the dominant trees in a given area. In Northwest Arkansas the color depends a lot upon the oaks.

"In a poor fall the oak leaves will turn brown and fall off," Wheeler said. "In a good year the hills will look inflamed."

Trees that turn yellow include ginkgo, green ash, tulip trees, hickory and elm. If you watch a particular tree, you can see how its color varies from year to year, Wheeler said.

The bright red trees peppering the landscape owe their brightness to sugar production and a pigment called anthrocyanin - the same chemical that makes beets red. When the weather cools, the trees make a tissue that seals off the leaf from the tree, which concentrates the sugars in the leaves. Red maples, sugar maples and blackgum, produce brilliant red leaves in good years. The reddish purple color of dogwood and white ash is caused by the same pigment.

"A blackgum in full fall color will look like a neon sign," Wheeler said.

To determine how bright the leaves may be this year, Wheeler suggests looking at the weather forecasts. A series of cloudy, misty days can slow or stop the leaves’ sugar production, dulling red colors. The weather may cool down and warm up several times, which can cause the before the colors peak.

Over the years, Wheeler has found a solution to the vagaries of factoring weather into fall foliage predictions.

"I always predict good years, and once in a while I’m right," he said.

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