Editor's note: the podcast episode above includes two stories. The first looks at where Chicago's bats call home. This biodiversity story starts at 8 minutes, 3 seconds.
Curious citizen Aaron Durnbaugh had nature on the brain when he asked us this question:
What part of Chicago has the most biodiversity (plant, animal, bird species)?
Maybe it’s no surprise that Aaron often has nature on the brain; after all, he’s the Director of Sustainability at Loyola University Chicago, and he’s spent a lot of time exploring the environmental richness of the region.
“My hunch is that it’s some of the remnant areas we’ve been able to protect. A lot of areas down on the South Side — Beaubien Woods, Powderhorn Prairie. ... That’s my hunch as to where our biodiversity is, but I’d like to get it confirmed,” Aaron told us.
But before we get to whether his hunch is right, first thing’s first: What, exactly, is biodiversity?
The right kind of variety
Biodiversity is, simply put, the number of species in any given area. That can include animals, plants, insects, fungi, microbes and more. But environmentalists and conservationists don’t just want as many species to live in one place as is possible — they’re often trying to create conditions for native species to thrive and alien invasive species to scram.
So while the Chicago Botanic Garden or the Lincoln Park Zoo might technically have a great deal of biodiversity, it’s not native biodiversity and that’s not the kind of answer Aaron is looking to find.
How to crack the numbers nut
We looked to Illinois Natural History Survey botanist and plant ecologist Greg Spyreas to help narrow our search Chicago’s biodiversity hotspot.
“So in a typically annoying scientist fashion, I am going to answer a simple question with a long contingency/caveat rich answer,” he said. “One of the most unifying generic rules in ecology (a large part of which is the study of biodiversity) is that the larger the area, the more species it will contain. So if we start with that rule, the largest natural area will provide habitat for the most species and be the most biodiverse.”
So that knocks out backyards and small parks. Spyreas said the next place to look would be habitat with the most habitat types (e.g., wetland, forest, grassland, bodies of water).
“In other words, if it’s a large area but it’s all like the Sahara desert — which is all a lot of sand as far as I know — that’s not going to hold a lot of species, because the habitat and types are very limited,” Spyreas said.
This clue means that we should look for an area close to Lake Michigan (or some other body of water) water within it — one that boasts a variety of habitats. Spyreas said there are some large forest preserves on the Northeast Side of Chicago, but those usually have just one type of habitat: forest. But Chicago’s far Southeast Side is part of the Calumet region, which boasts a network of preserves with varied habitat.
Spyreas said we should also consider so-called indicator species. “Those are species that only occur in areas that are so pristine that they are always accompanied by lots of others species,” he said. “It turns out that in areas like ours that have lost most of our natural areas you can look at where rare species are and they will tell you where the best overall habitats are.”
“So for my money, the Calumet region is the winner within Chicago’s city limits,” Spyreas said.
All signs point to Powderhorn
Spyreas said within the Calumet region there’s a preserve that nearly touches the Indiana border and lies just a few miles south of Lake Michigan. It’s called Powderhorn Prairie and Marsh and if we’re looking for biodiversity, it’s the place.
But before we could get too excited about this answer, though, we thought we’d get a second opinion, and we got it from Don Parker, a communications specialist for the Forest Preserve District of Cook County. We didn’t tell Parker about Spyreas’ guess but (much to our delight), he said the same thing: Powderhorn. So, two points to question-asker Aaron for having the right hunch.
Early one summer morning Curious City producer Logan Jaffe and I drove to Powderhorn, the idea being to gauge for ourselves whether there was something to the claims made about the place. But on our journey out there, we grew suspicious: the surrounding blocks leading up to Powderhorn’s parking lot were industrial; we heard airplanes buzzing overhead; and, across the street, trains would ding steadily along the South Shore line.
Logan and I joked that if we were plants, birds or animals, we’d seriously reconsider keeping this as a home.
But Chip O’Leary, a resource ecologist with the Forest Preserve District of Cook County, explained that the surrounding industry is actually one of the reasons why this spot has become so attractive to wildlife.
“Industry bought big tracts of land, but not all of it got developed. And this place didn’t get developed too heavily,” he said. As a result, it was accidentally protected as a growing Chicago spread in every direction.
Luckily the area also became officially protected by conservation groups. Powderhorn is 190 acres and a Cook County Forest Preserve holding. O’Leary said 130 of those acres have a another special designation: the first dedicated state nature preserve in the city of Chicago.
The magic of dune and swale
O’Leary described the unique habitat formation here: “So we’re sitting in the Chicago lake plain, which was a flattened area, formerly the lake bed of Lake Michigan. With each recession of the lake, it left behind a ridge. When the lake left, [it] created these long stretches of land ― these dunes. But in between those, there’s a lower spot filled with water, and then there’s another high dune left behind by the receding lake. As the lake receded, it left layers and layers of these dunes. And we’re sitting in a fragmented area of that dune and swale habitat.”
We couldn’t quite believe it ourselves as we traipsed through the preserve; on top of a small ridge we found plants typical of the western Great Plains and then, right next to them in an adjacent valley of the swale, we found swamp species more typical of places like coastal Louisiana. And in the midst of all that: prickly pear cactus!
O’Leary said this kind of dune and swale habitat is one of the most highly endangered systems in the United States. There are a few other scattered examples: some in Door County, Wisconsin another on Chicago’s North , and a few in Northwest Indiana.
“These habitats are very easy to develop,” he said. “If you think about having a sand dune next to a wetland, you can push the sand into the wetland and make a very nice flat area, and that’s what happened to the dune and swale area.”
Beyond the swale
The Powderhorn preserve has more going for it than just undulating dunes; it’s also part of a nexus of ecosystems in Northern Illinois: the boreal forest from the North, the plain prairieland from the West and forest species from the Eastern forests, not to mention an immense freshwater lake in the middle of it all.
Spyreas explained: “The Chicago Region probably has more habitat types and species than just about any other comparably sized area in the Midwest, due to if fortuitous geographic location, soils, topography, glacial history, lake Michigan, etc. And it is certainly one of ― if not the ― most important in terms of biodiversity. Here’s a jargony quote from an otherwise great botanical book called Plants of the Chicago Region: ‘It would be difficult to circumscribe another area of the North Temperate Zone with such geologic and physiographic diversity- our native flora, consisting of 1638 taxa, reflects this.””
Who and what is at home at Powderhorn?
According to O’Leary, Powderhorn Marsh & Prairie currently houses about 250 plant species, 2,500 insects, but he said it may be more. “Bird species ― depending on the time of year ― there’s anywhere from 40-100 species, including osprey,” he said. “There are of course reptiles, lizards and fish using the lake. It’s a wild set of things, the total number, I haven’t added up.”
In terms of furry critters, Chip said there are the usual suspects that appear in other parts of the city: squirrels, chipmunks, white tailed deer, raccoons and opossums.
And what about plants? O’Leary rattled off a some of the fabulously-named species: slender false foxglove, tickle grass, nodding onion, lowland hog peanut, indian hemp, cat’s foot, nodding bur-marigold, blue-joint grass, buttonbush, partridge pea, swamp thistle, false toadflax (otherwise known as bastard toadflax), winged pigweed, marshfield fern, cinnamon willow-herb, purple love grass, white snakeroot, rock-rose, water stargrass, hairy hawkweed, St. John’s wort, orange jewelweed, blue flag, hairy pinweed, fall witchgrass, round-headed bush clover, rough blazingstar, Turk’s cap lily, hoary puccoon, common water horehound, monkey flower and horsemint.
With a list this long, we were curious whether we had exhausted O’Leary’s knowledge or maybe O’Leary himself. Turns out, neither was the case.
“There are some threatened and endangered species in every site that we don’t mention to the public in order to protect them,” O’Leary explained. “People will come out and poach them. Some folks are just collectors and want the plant in their garden. Some folks use them as herbs.”
But how can you be sure of the biodiversity level?
When we asked Spyreas if it’s even possible to be sure this is the most biodiverse spot in the city limits he said this: “The honest answer is that you can’t be sure. Nobody has counted every plant and animal in the Chicago area for sure. Nobody’s done it. There’s so much diversity and expertise involved and plants and animals are constantly moving and it’d require a lot of work.”
Spyreas added that, except for a park or preserve with a very active volunteer group or site manager interested in tracking biodiversity, most places don’t keep a running list of what’s on site. He said people instead focus on rare and endangered species, and tracking those can sometimes only be done by people with rare and specialized knowledge.
But given the general rules of Ecology, and the vast collection of species found at Powderhorn by experts and enthusiasts, it’s the best guess there is. If you have reason to believe otherwise we’re all ears! Comment below.
After our foray into the marsh and prairie, we rang up Aaron to tell him he was right and he was delighted to hear it. “I’m glad to know it’s so close!” he said. “I can take my five-year-old out there and get some nature and get a little lost.”
And when we asked him why biodiversity matters to him, he had plenty to say.“I’m just interested in the way biodiversity brings richness in our lives. The way we can walk out the door and have a rich connection to the natural history in our region. We’re not some other generic place — we’re Chicago. We’re this land of prairies and wetlands and lake Michigan and rivers, and there’s a richness and identity to that we often overlook, over-pave and over-develop. It’s also just as much a part of who we are as the stockyards, as the city of the big shoulders, Al Capone and Michael Jordan. We are the city that’s really the gateway to all these tremendous natural resources. That’s part of the reason why we developed. I hope people recognize that connection and see that biodiversity adds to the richness of our lives in Chicago.”
We couldn’t have said it better ourselves.
Correction: An earlier version of this story suggested that pocket gophers can be found at Powderhorn Prairie. That is not the case. Resource Ecologist Chip O’Leary says pocket gophers live 50 miles south of Powderhorn, near the Kankakee River.