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Nature's Technicolor Dreamcoat: The science of fall color

brilliant red fall color of Eastern Wahoo shrub

You feel it, don't you? Sunrise coming later, sunset earlier, and the roller rink of acorns underfoot. The change of seasons is well underway. And just as you are pulling out your flannel shirts, wool socks, and warm gloves the trees and shrubs are also pulling out their fall wardrobe.

The vivid reds, rich purples, buttery yellows, and that almost indescribable fiery rosy orange of Illinois' deciduous trees and shrubs are a visual feast! Fall color in the Upper Midwest is so striking some years, it can be seen from NASA's MODIS space satellite

What makes fall color? 

What makes fall color? And why are the colors far less brilliant and washed out some years? The question "when will the trees put on their fall color?" should really be "when does the chlorophyll leave the leaves to reveal the fall colors?"

Think of wearing your favorite green sweatshirt. You wear it when you need it, but when you no longer need it you take it off revealing your Illini orange T-shirt underneath. The orange was always there, just not visible under the green. You had to shed the green to reveal the orange. Trees are the same.

When trees need their green, the pigment chlorophyll, they awaken from dormancy in spring as the days lengthen and foliate putting on abundant, lush green growth. Through chlorophyll and photosynthesis leaves become food factories, eating carbon dioxide and water and cooking with sunshine to produce their own food-sugars. That energy from sugar rockets out new shoots and fresh growth and storage of food as a sack lunch for later in their trunks and roots. But as daylight shortens, trees start to push themselves away from the dinner table and prepare for their fasting period-winter. Low temperatures and bright sunshine destroy chlorophyll. As it leaves the leaves (pun intended), amazing pigments already underneath are revealed.

Buttery yellows and bright orange - Carotenoid and xanthophyll

Carotenoid, the orange pigment, and xanthophyll, the yellow pigment, are responsible for producing the color of carrots, bananas, squash, daffodils, sweet potato and pumpkin as well as the yellows and oranges of fall color. These pigments were there in leaves all the time, but chlorophyll is a more overpowering pigment; carotenoids and xanthophylls are just waiting for their reveal party scheduled for shorter daylengths and cooler temperatures. Spicebush (Lindera benzoin) and Buttonbush (Cephalanthus occidentalis) display a buttery yellow, while 

Ravishing reds - Anthocyanins

Other pigments, however, aren't in the leaves all summer, but are only produced once the day length shortens. The anthocyanins produce the brilliant reds in fall leaves. Nothing more striking than the blazing red of the Eastern Wahoo (Euonymus atropurpureus) pictured above. Who needs the now invasive burning bush (Euonymus alatus) when we have this native beauty to light up a landscape? 

Anthocyanin pigments are also responsible for the colors in blueberries, cranberries, and native serviceberries (Amelanchier spp.) Anthocyanins are made when we have sunny warm days and the trees are still producing sugars, contrasting with cold nights. These sugars remain trapped in the leaves, making the red pigment. You also see this red trapped sugar effect on some annual plants like marigolds in the spring when temperatures dip and the foliage shows a smattering of plum-coloring.  

Whether the weather

Weather plays a big role in how bold and big nature's palette and paintbrush are each year. The most brilliant fall foliage colors occur after summers with adequate moisture following into autumns with dry, sunny days that are followed by cool, dry nights. In 2021, much of Illinois was expecting a bold color show until the long dry summer dragged on into an extremely warm late October followed by some heavy rains. But as with all things nature, the fall colors don't always follow the playbook and sometimes we will have outstanding fall color even without ideal conditions.  

As you enjoy a hike this fall in the cool, crisp weather, those fall colors may now seem more alive than ever. 

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Nancy Kuhajda is the Agriculture and Natural Resources Program Coordinator for the Master Naturalist, Master Gardener and Master Composter Programs in Will and Grundy Counties in Northeastern Illinois. Nancy has a bachelor's degree from the University of Illinois at Urbana Champaign and has Graduate Certificates in Crop Science and Horticulture. Nancy also writes a weekly column for a local Joliet paper on nature and gardening topics and is a well-known speaker in the Chicagoland area. Nancy's passion is to bring understanding of the natural world to the community at large but particularly to underserved populations--urban youth, special needs individuals, and elderly in congregate housing. 

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