This Chicago fire is one of leaves. Whether you travel to the Windy City by air, train, or car, inescapable flames of leaves blazoned by the sun and fanned by the wind surround you.
Chicago’s Hardwood Forest
The kaleidoscope of fabulous color in the hardwood broadleaf forest enchants native Chicagoans and visitors alike. The wash of pigments changes week-by-week, day-by-day, and even hour-by-hour. One awakens to a yellow horizon and falls asleep to an orange skyline.
As leaves fall, nature’s color scheme creates a collage carpeting of decorator color chips – green, yellow, orange, russet, red, burgundy, purple – to walk through or bicycle across, to rake into bonfire piles, and to collect for pressing souvenirs of fall.
Colorful leaves are accessorized with tree jewelry like shagbark hickory nuts, chinquapin oak acorns, catalpa pods, hackberry drupes, and box elder paired samaras.
Factors Influencing Leaf Color
The display of sequential warm color will last through November. What causes the dramatic color change? Scientists know many factors, genetic and environmental, contribute to any fall foliage display.
Just as animal species have their own schedule for growth and development changes, each species of tree has its own pace and pattern of color change set, in part, by genetics.
Weather is one key factor and includes rainfall and both day and night temperatures. Chicago trees have received plenty of rain this growing season. Adequate rain contributes to healthy trees, which soak up solar energy.
Sunlight, its intensity and duration, affects photosynthesis. Shortening daylight slows production of chlorophyll and unmasks the carotenoids, the hidden yellow pigments. Buckeyes, sycamores, yellow poplar, hickories, ash, and birches turn yellow.
Sunny days in conjunction with cool nights cause trees to utilize stored energy and increase sugar production magnifying the red color in leaves. The reds and purples are anthocyanin pigments made in the sap of the leaf in late summer. The brighter the sunlight, the brighter the colors will be. In Chicago the maples, oaks, sassafras, and sumacs turn vivid scarlet.
Evolutionary theorists W.D. Hamilton and Samuel P. Brown have proposed a unique theory on the function of anthocyanin red leaf color. They propose that the healthiest trees show the brightest red colors. Furthermore, they speculate that red is a defense signal to fall-feeding insects to stay away from the healthy trees.
Natural Recyclers
Color change is only part of the story of autumn leaves. For a tree the changes in leaf color are followed by falling leaves. The tree recycles nutrients in the leaves back to the earth for future use. Trees are recycling, composting, and mulching experts. Perhaps the bright colors are a signal for us to do the same.
Chicago’s Urban Forest
Former Mayor Richard M. Daley made tree planting a priority within the city of Chicago for the past twenty years. Under his leadership millions of trees were planted throughout the city. In August 2011 Chicago Mayor Rahm Immanuel launched an updated Nature and Wildlife Plan, which includes the commitment to preserve and expand the tree canopy.
An urban tree canopy is desirable for many reasons. The tree canopy filters the air, shades buildings and reduces energy usage, buffers noise, holds moisture, and increases property value.
The city of Chicago’s urban tree agenda speaks to every tree within the city limits - trees on parkways, medians, parks, school campuses, forest preserves, backyards and community parks - with four main goals:
- Sustaining and conserving trees
- Expanding the urban forest
- Connecting green infrastructure
- Advancing stewardship
The Chicago Trees Initiative is working to ensure Chicago’s urban forest will offer flamboyant autumn color for generations yet to come.
Chicago is a green mansion destination in the summer and a conflagration of color in fall. Keep the fall fire burning by planting a hardwood tree on Arbor Day.
Sources
- “An October Fall-Color Tree Walk,” Chicago Botanic Garden website
- “Chicago’s Urban Forest Agenda,” City of Chicago website
- Chicago Trees Initiative website
- Dawson, Jeffery O. “Why Tree Leaves Turn Color in Autumn,” Illinois Forestry and University of Illinois Extension website
- Hedborn, Ed. “Why Leaves Change Color,” Morton Arboretum website
- Richards, Cindy. “Fall Foliage for First-timers,” Going Places, Fall 2011 and reprinted in Chicago Parent website October 14, 2011.
Arlene Marturano - Arlene Marturano, an educator, consultant, master gardener, and writer advocates gardens as a context and gardening as a tool for ...
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