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Red, Gold, Yellow and Orange: Fall Colors Hidden Beneath the Green

People biking and walking on the North Branch Trail at Bunker Hill in fall.

While all seasons provide something new to see in the Forest Preserves of Cook County, fall may arguably be the most visually stunning time to get out and explore. There are still some late-blooming wildflowers, and of course, canopies are exploding with vibrant colors. But what exactly is causing the leaves to become red, gold, orange and yellow?

Rebecca Collings, Forest Preserves’ senior ecologist, explains that leaves aren’t actually turning a different color—different pigments that have always been present are just becoming visible.

“We always hear people ask, ‘When are we going to see the leaves change?’ But the tree isn’t necessarily changing colors. As the tree prepares for winter, it decreases its chlorophyll production, the green pigment that helps plants photosynthesize. Other pigments are present, but are masked by chlorophyll,” Collings says. “When trees stop making chlorophyll, these other pigments become more visible, and that’s when people will see the radiant yellows and oranges.”

Why do trees stop photosynthesis? There is still sunlight during winter.

For trees to photosynthesize—the process plants use to convert sunlight into energy—they absorb carbon dioxide in the atmosphere and water through their roots. Through photosynthesis trees are able to produce carbohydrates to make tissues and grow.

“In order to absorb the carbon dioxide, the plant has to open up small holes in the leaf called stomata,” explains Collings. “Doing so is a risky for the plant as they also lose water in the process. Some plants, like our deciduous trees, ultimately decide it is a better use of resources to drop their leaves and regrow new ones next year. Essentially they’re in survival mode till next spring.”

What about the trees that stay green, like conifers and evergreens?

These trees will continue some level of photosynthesis in the winter. They have adaptations like small leaf surfaces, meaning fewer stomata on each leaf, and waxy coatings that limit water loss.

Where can I go to see stunning fall color?

Want to experience breathtaking color this fall? Check out this list of recommended hikes and biking trips:



  • Harms Woods – Park at Harms Woods Central to access unpaved Yellow Trail or paved Red Trail
  • North Branch Trail – Park at Miami Woods, north of Oakton. Cyclists can enjoy a ride through a tunnel of maples


The Salt Creek Trail System sees a lot of bicyclists. Consider bringing a bike, or renting one in the Forest Preserves.



  • Jurgensen Woods – Access unpaved Yellow Trail and hike through Jurgensen Woods Nature Preserve
  • Sauk Trail Woods – Park at Sauk Trail Woods Central for bike rentals and explore 3.5-mile paved loop trail around Sauk Trail Lake