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Arboretum scientists study why leaves change color amid Fall Color Festival events

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LISLE, Ill. (September 22, 2022)—Following a fall with less than vibrant leaf colors in 2021, tree scientists at The Morton Arboretum say the Chicago region is poised for a more usual leaf-changing season, largely thanks to more typical rainfall over the summer.

When will be the best time to catch the best fall color views? According to Christy Rollinson, Ph.D., forest ecologist at the Arboretum, “It’s more a question of where to see changing colors rather than when to see them, since different species change at different times.” Places like the Arboretum, where there is a large amount of tree species diversity, will have something to see all season long, she noted. Some fall colors are already emerging throughout the Arboretum, which visitors can track in a weekly Fall Color Report on its website blog.

Rollinson said that while mid-to-late October is generally the best time for leaf vibrancy in the Chicago area, it can shift a couple of weeks either way, depending on factors such as temperature and precipitation.

Researchers at the Arboretum are still seeking to more fully understand what ultimately drives leaves to change from green to the array of vibrant colors of fall. They are collaborating with institutions across the country to decipher the causal relationship between weather and the timing of fall color.

A practically endless web of variables means that even in an unremarkable weather year, Rollinson and her team are using the tools at their disposal to learn more about the seasonal changes. “At The Morton Arboretum, we’re starting to harness satellite imagery to monitor trees and color change at a scale of observation that’s exponentially greater than we’ve had in the past,” she explained.

She said that it’s widely accepted that the main driver of leaf color change is shortening days and cooler temperatures that creep in during late September. However, many scientists have seen evidence that season-long climate factors can play a role as well. Although patterns like drought are often associated with early fall color, Rollinson says that recent research suggests that trees can only store a certain amount of carbon in a given growing season, and when they’re done working hard and have stored as much carbon as they possibly can, they drop their leaves. This means, according to Rollinson, in a year free from extreme weather like 2022, that trees may show average or early fall color even if the first freeze is still weeks away.

“Many areas of the country are facing drought and simultaneously seeing early fall color changes,” she explained. “With the new technology, we’re now able to go beyond field observations and take in more data points to help us predict natural events, like fall color changes, more accurately.”

Fall Color Festival

Amid the changing trees, fun festivities for all ages are held at the Arboretum throughout October as part of its Fall Color Festival. Events celebrating the season include the Fall Color 5K Run and Walk, Oct. 1; Fall Color Wine Tasting, Oct. 6; The 12th Annual Glass Pumpkin Patch; Oct. 12 through 16; Cider and Ale Festival, Oct. 22; Scarecrow Trail, daily in October; and Walking Plays: “Winnie the Pooh,” weekends Oct. 1 through 30.

Also, on weekends in October and Oct. 10 (Columbus Day/Indigenous Peoples’ Day) from 11 a.m. to 3 p.m. in the Arbor Court area outside the Visitor Center will be seasonal concessions, including apple cider doughnuts, taffy apples, cotton candy, warm kettle corn, chili and a selection of craft beers and warm beverages.

In addition, special fall-focused programs include Fall Native Plant Propagation, Oct. 15 and Fall Foliage Walking Tours, Oct. 21 or 28.

For more information about Arboretum programs and special events, visit mortonarb.org.