A Horticultural Haven: News from Nature Boardwalk

Millions of Chicago residents walk through, bike, or run into the zoo’s 14-acre Nature Boardwalk every year—but most may not realize exactly what goes into making sure this beautiful place, overflowing with plant and animal life, thrive. From everyday maintenance to annual assessments, the zoo’s horticulture staff works hard to ensure this place is a haven for all.

As an accredited botanic garden and arboretum, Lincoln Park Zoo has been recognized for its commitment to plant conservation and care as well as animal welfare. That’s why, every year, the Horticulture department does an annual survey called a Floristic Quality Assessment—or FQA—of the zoo’s Nature Boardwalk. This mid-season assessment works to document what plants exist here, with a focus on understanding local plant communities along with the overall quality of the habitat.

The Floristic Quality Assessment

To complete this work, zoo staff conduct a survey that assigns a value to two characteristics of native plant populations. These characteristics include a plant species’ tolerance to stress and disturbance (from elements such as geese, drought, flooding, or unleashed pets), as well as the species’ ability to thrive in habitats with varying quality. The relationship between these two characteristics is called a coefficient of conservatism, and this describes how conservative (or picky!) a plant is about growing in different environments.

The shooting star (Dodecatheon meadia), is a spring wildflower with white or purple flowers that only blooms for a short amount of time. This is one of the earliest flowering wildflowers at Nature Boardwalk. so it’s worth trying to find as the weather warms up.

The FQA doesn’t look at every type of plant the way a census might; instead, it looks at random sample sites. This method tends to leave out plants that are not abundant at Nature Boardwalk, giving a better sense of which plants are truly thriving here as compared to simply inventorying all the plant species that exist on the site. Such information is especially helpful when tracking how well threatened or endangered plants are doing at Nature Boardwalk.

The State of Nature Boardwalk

Since Lincoln Park Zoo started doing FQAs in 2016, the species richness of the habitat at Nature Boardwalk has been slowly increasing. This could mean that more native plants with a higher conservation value are in greater abundance there. It definitely means that this area, which started out as turf-grass lawns used for human recreation and was reconstructed within the last 20 years, is doing well, thanks to thoughtful management, maintenance help from contractors, and work to reduce invasive plants done by zoo volunteers. “This has significantly decreased the number of weedy natives and invasive plants growing at Nature Boardwalk,” notes Director of Horticulture Katrina Quint.

The rattlesnake master (Eryngium yuccifolium) is the host plant for the rare rattlesnake borer moth, once thought extinct in Illinois. The moth was rediscovered in this state in 1989 and placed on the state’s Endangered and Threatened Species List. It’s a pollinator powerhouse plant that can be found all over Nature Boardwalk.

There’s more progress to be made, of course. The current numbers put Nature Boardwalk at a medium to high “Intermediate Quality” level—a great result for a human-made prairie ecosystem—and Horticulture staff would love to increase that to a “High quality” status, which is a lofty (but not impossible) goal. Currently, Nature Boardwalk includes 346 living taxa, or types of plants, along with spontaneous plant communities The boardwalk is also home to hundreds of trees and shrubs that make up different ecosystems.

Over the years, staff have identified several species of concern—basically, six species of weeds to reduce and two native species to encourage the growth of. The six weedy species include an invasive cattail hybrid called Typha x glauca, which was not found in this year’s survey. That’s a great sign. Other species being monitored include Canadian goldenrod (Solidago canadensis), tall goldenrod (Solidago altissima), eastern cottonwood (Populus deltoides), creeping thistle (Cirsium arvense), and lesser burdock (Arctium minor).

At the same time, the zoo is working to increase the growth of two species: the lead plant (Amorpha canescens) and leafy prairie clover (Dalea foliosa). In 2024, as part of a managed plan, staff collected seeds from the leafy prairie clover that are intended for propagation and reintroduction back into the Nature Boardwalk ecosystem. “These plants exhibit high fidelity, which means they are mostly able to thrive in high-quality environments,” explains Manager of Plant Records and Horticulture Programs Emily Conn. “Their presence and expansion is a good indicator of the improving quality of the environment.”

What’s Next for Nature Boardwalk

In early 2024, Nature Boardwalk underwent a controlled burn to reduce the buildup of plant biomass and reduce the spread of invasive plants—part of the ethical management for the area. Over the summer, it was discovered that there are now fewer populations of Canada goldenrod, a weedy species, which may be the result not only of the burns but of management practices such as early-season targeted pesticide applications. By implementing multiple management techniques such as these, the zoo will continue to make the environment more habitable for native species. Horticulture staff members will continue reporting on the eight species of concern and refining methodology to make more precise observations.

The jack pine (Pinus banksiana) is an endangered tree in Illinois. It is a pyrophyte, which means it actually requires fire to germinate its seeds! This is just one example of how ecosystems like Nature Boardwalk rely on prairie burns to regulate the health of the environment.

In the meantime, staff have focused the management of the space by separating it into five different ecosystems: shortgrass prairie, tallgrass prairie, wetland, woodland, and black oak savanna. “The black oak savanna was planted to create an ecosystem that may have naturally occurred in sandy areas along Lake Michigan,” Quint says. “Black oaks are native to much of the eastern U.S. and are found throughout Illinois in natural populations. They grow in upland woods, rocky open woodlands, and sandy areas, and their preference for dry soils makes them a good choice as we look towards climate-resilient species.” By dividing the area into these separate ecosystems, the zoo is able to manage the space for greater species diversity, improving the quality of the habitat for urban wildlife.

Sampling for future FQAs will continue to take place throughout the summer, twice a week for 2.5 hours each time, in all 100 quadrants of Nature Boardwalk. In addition, zoo staff are working toward a full inventory of Nature Boardwalk. Naturally, this is a moving target. “Any plant inventory of a naturalized area is an ongoing process since plants die, and other species may spring up in their place,” Conn says.

Joe Pye weed (Eupatorium purpureum), pictured here, is a plant native to Illinois. Like milkweed, purple coneflowers, waterlilies, and fall-blooming asters, these are charismatic plants that are easy to find at Nature Boardwalk because of their distinctive appearance. 

As winter weather gives way to spring, all this care will be readily apparent in the lush plant life that blooms and provides an urban oasis for residents of Lincoln Park as well as visitors to the area. It may not look as cultivated and manicured as landscapes within the zoo and at Café Brauer, but that’s part of its charm. The beauty and diversity of species that you see bursting out seasonally all over this natural green space is no accident—and thanks to zoo horticulture staff, it’s only getting better, in every sense of the word.