Myth: The Mighty Oak Will Always Flourish in Illinois

Root for the Home Team: How and Why to Support Local Oak Trees

Strength, protection, endurance, Chardonnay…these are all words associated with the mighty oak. In Illinois, we love the acorn-bearer so much that we named one of them our official state tree. (That would be the white oak, or Quercus alba for you crossword fans.) For many of us, an oak-lined street or oak-dotted prairie is one of the most iconic features of the Illinois landscape. But are oaks as mighty as they appear? And can we count on them to maintain their local grandeur for the generations to come?

We chatted with a trio of experts on the subject—the Morton Arboretum’s Forest Ecologist Bob Fahey, PhD, Plant Systematist and Herbarium Curator Andrew Hipp, PhD, and Botanic Gardens Conservation International’s Executive Director Andrea Kramer, PhD—who all agree that we can’t expect our oak forests and woodlands to look the same in the future if we don’t take action today.

Not Branching Out: Why Old Growth Doesn’t Mean New Growth

There’s a reason many of us assume oaks are doing just fine in Illinois: Looking around, it’s clear they’re still the dominant tree in the area, at least, as Fahey says, in terms of biomass. But he explains that this visible abundance is predominantly made up of trees that are between 150-200 years old…which would be fine and dandy if the next generation were right behind to take their place.

“The issue isn’t that they’re all gone, the issue is more that they’re all old, and will start to die in the next 50-100 years,” says Fahey. It can take up to 50 years for an acorn to grow into a full-grown tree, and the generation that will replace the large oaks we now see doesn’t exist right now. “If we want [the new generation] to be there when [the current oaks] die, we have to act now,” he states.

So why is the new generation so behind on the game? Here’s the deal: Oak trees thrive once they’re in the canopy (aka, closest to the sky), but they need a lot of light to grow up there in the first place. New seedlings and saplings have trouble competing in more crowded settings, so they’re being pushed out by other species. Fahey says this regeneration problem isn’t unique to Illinois. In fact, it’s occurring in many places throughout the northeastern U.S., especially in areas with high water and nutrient availability.

He takes us on a little history tour to explain what scientists are seeing across the country. Before settlement, “landscape-level fires were really common. They would knock back a lot of the other species like maples, basswood, and ashes and keep them from dominating the landscape.” That process helped maintain the more fire-tolerant oaks, but now that fires are less common, the more shade-tolerant species have come in and started to fill up the understory, he says.

So now we’re in a situation where the canopy looks like oak central, but the base layer is filling up with other trees and a few relentless shrubs. Invasive shrubs like buckthorn and honeysuckle, specifically, are a growing threat to oaks, because, as Kramer says “they’re choking out growth of any new oak seedlings.”

Right. So far our oaks are challenged by a lack of fire, invasive plants, and other native tree species. Any oak-zapping diseases we should know about? Some people have asked if there’s something equivalent to the emerald ash borer for oaks. The answer is…yes and no.

“Pests and diseases are less of a concern for oaks in Illinois than they are for other species like ash,” begins Fahey. While gypsy moths can defoliate Illinois oaks, they won’t usually kill them. There’s also oak wilt, which does kill oak trees, but he says it doesn’t spread around the landscape as well as something like dutch elm disease or emerald ash borers. And for those of you who’ve heard of the chill-inducing sudden oak death, Kramer, whose own research focuses on oak species in the southeastern U.S. and California, confirms that it doesn’t exist here yet, and isn’t a present threat thanks to our cold winters. But they both caution us from overly celebrating this information. “You never know with these types of pathogens—we don’t understand them that well and they can change pretty quickly,” notes Fahey.

A New Leaf in Forest Research and Management

Saplings can take up to 50 years to reach full-grown glory. (Photos by the Morton Arboretum)

Planning for the unknown is one of the big challenges facing Morton scientists and BGCI’s partner botanic garden researchers today.

Hipp studies oak biology in the Morton Arboretum lab, evaluating the gene flow within populations and species in the area. This knowledge helps scientists understand the traits that govern where oaks live, how they evolve resistance to herbivores, what habitats they prefer, and how they’ve evolved in response to past climate change—all so we can begin to assess what potential response oaks will have to future climate change.

As Fahey says, “lots of this work has to do with how these trees might deal with climate change in the next 50 years.” And while oaks are a vital part of that picture, other species will be a factor too. He cites the example of a sugar maple, which has begun replacing oaks as the dominant tree in local woodlands.

No one is saying sugar maples are bad, but the idea of them taking over as the dominant tree could be problematic. For one thing, Fahey says, they’re not very drought-tolerant, which means they might not respond well to climate change. There’s also the Asian longhorn beetle, which kills maples. There was an outbreak of this pest in Chicago in the 1990s, but a successful eradication effort was conducted and it hasn’t been seen since. It has since popped up elsewhere in the U.S. and could be back any time…

On a similar note, both Kramer and Fahey say that 10 years ago, no one could have guessed the emerald ash borer would cause the widespread devastation that it now has. These are all just examples of why it’s important to understand how different tree populations can regenerate when faced with different environmental challenges, from disease to climate change to invasive species.

The bottom line, according to Fahey, is that “we don’t want an urban forest canopy dominated by one species because a disease or pest could come along and wipe it out or it could respond poorly to climatic changes. A more diverse canopy is likely to be more resilient to these types of stressors.”

Take ‘Em or Leaf ‘Em?

We’re just gonna say it: Oaks matter. Yes, part of it is emotional—oaks are a part of our local identity. But there’s more to it than that. “There’s a very strong sense of place that comes from the huge beautiful oak trees that hold onto their leaves in the winter,” suggests Kramer. “But they’re also a huge source of food for wildlife in ways that not every other tree is.”

And it’s not just the wildlife that benefit, she stresses. Research shows oaks have a big impact on plant communities as well, in part because their leaves decompose much more slowly than buckthorn or maple leaves. “This means a lot of really good leaf cover to support soil microorganisms through the winter…which in turn support more diverse insect communities…which in turn provide a sort of insulation that plants like trillium need to survive the really harsh winter,” she explains.

Never underestimate the power of the acorn! (Photo by the Morton Arboretum)

Essentially, oak trees are worth conserving not only for their good looks, but also for their role in supporting local wildlife and other trees and plants we know and love. So how well do you know your oaks?

See the Forest for the Trees: Getting to Know Our Illinois Oaks

According to Hipp, there are approximately 415 species of oaks worldwide, and 220-230 in the western hemisphere. In the Chicago region we’re host to about 15 species, of which nine are native.

The most dominant species around here have long been the white oak, bur oak, red oak, black Hill’s oak, and swamp white oak, according to Fahey. Some are faring better than others. The bur oak has become less successful in recent years because it’s extremely shade-intolerant and only grows and regenerates in open areas like savannas. But since such a big proportion of those areas has been converted to agricultural lands, explains Fahey, the only way to bring them back in force would be to restore oak savannas—which would require active management to keep invasive shrubs from taking over.

If you’re wondering what a restored oak stand looks like, check out these experts-recommended areas around Chicagoland:

  • The Morton Arboretum’s Heritage Trail: This 1.3-mile trail showcases how things like fire, soil, and human habitation have impacted woodlands. For more visual comparisons, head west on Woods Road to see one how side of the road has been burned annually for 20 years and is an open woodland with lots of light and herb species, while the other unburned side is filled with shrubs).
  • Somme Prairie Grove: Hike along the outer or inner trail to see actively managed savanna and oak woodlands in one of the region’s first woodland restoration areas.
  • The Chicago Botanic Garden’s McDonald Woods: A 100-acre oak woodland reveals the significance of biodiversity, with 400 species of native plants. For further illustration that thoughtful forestry management matters, follow Green Bay Road just south of Lake Cook to see restored oak groves on one side, and an area overgrown with buckthorn across the street.

Looking for more inspiration? Our experts get a little sappy (pun intended) about their fave oak spots around Chicagoland:

  • Kramer: The bur oaks in the Chicago Botanic Garden’s oak savanna and Somme Prairie. “I got married in an oak grove. I love them, so I’m a little biased.”
  • Fahey: Ryerson Conservation Area and MacArthur Woods. “We’re working with Lake County to do restoration work in the future—places that are beautiful woods now and that we’re hoping to perpetuate.”
  • Hipp: Glacial Park in McHenry County (“gorgeous, rolling, open”), Thorn Creek Woods Nature Preserve in Will County (“a dynamite black oak wood like no place I’ve ever seen before”), and the East Woods of the Morton Arboretum.

EcoMyth Outcome

Myth busted. While the oak species we find in the Chicago region will probably still be present at some level in 50-100 years, the oak communities we see today will look very different. Without action, future oak tree populations and oak-dominated ecosystems may not be able to flourish as they do today.

One Green Thing You Can Do

Volunteer with your local forest preserve or with Morton’s woodlands steward program in brush cutting and other oak work. You’ll learn a lot, get outside, and feel good all at once.

More ways to help:

  • If you’ve got a yard, talk to an arborist about planting an oak. If not, talk to neighbors and community associations about planting them in the community.
  • Be the eyes and ears: If you see unhealthy oaks, notify Morton or the Chicago Botanic Garden so they can help advise, as well as monitor local oak populations.
  • Support organizations that research and promote oaks in the region.

2 thoughts on “Myth: The Mighty Oak Will Always Flourish in Illinois

  1. Awesome article! Thanks for busting that myth!

    For those in McHenry County, please check out The Land Conservancy of McHenry County’s website: where you can find a lot of information about our local oaks and ways you can get involved through Project Quercus (Quercus is Latin for oak!).

    85% of the oak woods remaining in the county are on private land – the character of our community in the future will be determined by the decisions those landowners make to preserve, restore or develop their land – that is who Project Quercus targets.

    Oaks will be part of our community 100 years from now if we all do what we can. From planting memorial trees to collecting acorns in the fall and surveying private oak woods, individuals can make a difference that will last for generations!


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