Leaves already have begun turning color in the Quad-Cities, with the brilliant yellows and deep purples of various ash trees leading the way.

But as for the rest of the fall color show, it “could be intense, but short,” said Jeff Iles, the chairman of the department of horticulture at Iowa State University in Ames.

Leaves always turn color in the fall because of seasonal changes, but this year, some of the color — or lack thereof — is likely because of stress brought on by the continuing record drought, he said.

Maple trees, normally some of the showiest, might be the biggest disappointment, he added.

Many maple leaves are scorched — that is, they have turned brown — because of the lack of moisture, leaving less area for pretty colors. In addition, many trees have prematurely lost quite a few of their leaves.

“The maples might look a little rough,” Iles said.

“The trees that won’t miss a beat are the oaks,” he said. “The red and white oaks are pretty tough.”

Generally, the best fall color comes about with cool nights and warm, sunny days, preceded by a season of ideal rainfall. While the cool nights/sunny days portion of the equation describes recent Quad-City region weather, the area is about 9 inches below normal rainfall.

Because of that, trees are stressed — with stress defined as exposure to unfavorable conditions, explained Rhonda Ferree, a horticulture educator with the University of Illinois Extension.

“One sign of plant stress is early fall coloration,” she said.

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That is because the tree, with little moisture in the ground, is deprived of water and nutrients and goes into a bit of decline. With fewer nutrients, the amount of chlorophyll (the green pigment used in photosynthesis) breaks down, revealing colors such as yellow and gold that were there all along but masked by the green.

In a normal year, the green breaks down in response to shorter days and declining intensity of sunlight.

The red, purple and crimson colors of some leaves are produced by a different pigment that shows up only in the fall when warm, bright days favor its production.

“The color is happening a little sooner than normal and probably won’t last as long,” Iles concluded.

Ferree recommends watering plants that are stressed to encourage recovery growth and root revival.

“Apply enough water to penetrate deeply within the drip line,” she said. “The added water will better prepare the plant for winter and possibly less future decline.”