The Importance of the Mighty Oak

Think of your favorite wildlife: white-tailed deer, woodpeckers, white-footed mice, nuthatches, owls, squirrels. In one way or another they all depend on oak trees for food or shelter. That’s why oaks have been an important part of a decade-long look at the trees that live in DuPage County’s forest preserves.

Between 2006 and 2016 ecologists took pencil-thin core samples from 27 different kinds of trees — over 1,500 individual trees in all, each between 3.5 and 50 inches in diameter. By subtracting the number of annual growth rings in a sample from the year the core was extracted, ecologists were able to calculate each tree’s “start date.”

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Although there were some “teenagers,” oaks made up 88 percent of sampled trees with start dates before 1900. At Wayne Grove and West Chicago Prairie forest preserves, ecologists found bur oaks that were mere seedlings when the Declaration of Independence was signed. Not as extreme but just as significant, the majority of white oaks dated back to the 1840s, 50s and 60s. (It made sense many weren’t older; in the mid to late 1800s European settlers cut down oaks in large numbers for homes and plank roads.)

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For oaks to continue to enrich the landscape (and support the wild animals that rely on them) a new generation of oaks is going to need to fill the ecological shoes of today’s mature trees. But research shows that this isn’t happening. Oaks require a fair amount of light to mature, and many aren’t getting enough. Basswood, sugar maple, wild black cherry, ironwood, American elm, slippery elm and other trees that do well in low light are taking over, making the ground even shadier for oak seedlings. But by using core samples and other methods to analyze the county’s woodlands, the Forest Preserve District can determine where to remove shade-tolerant trees to give the county’s young oaks a better, sunnier start.

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