About 4 miles from the Chicago Rockford International Airport, violet wood sorrel has started to grow.

The low-lying Illinois native with delicate, trumpet-shaped flowers is a sign of hope for those involved in a last-ditch effort to save some of the soil disturbed by a new road that will run through the heart of Rockford’s ancient Bell Bowl Prairie.

After environmentalists lost their high-profile battle to reroute the road in March, the airport, which owns the prairie and is building the road, allowed the Forest Preserves of Winnebago County to haul away about 20 dump trucks of topsoil that had been removed during construction.

[ Rockford Airport expansion in Bell Bowl Prairie begins Thursday despite push to protect endangered bumblebee’s habitat ]

The Forest Preserves district spread most of the soil over 1 acre in a prairie restoration area at Cedar Cliff Forest Preserve, in the hope that the plants and insects of Bell Bowl would once again flourish.

“Already we’re seeing some very cool things,” said Forest Preserves of Winnebago County’s director of natural resources, Mike Brien, who spotted the violet wood sorrel growing in the Bell Bowl soil a few weeks ago. He said the plant hadn’t been present at the preserve before the soil transfer.

He also noted that volunteers who had sifted through a portion of the recovered Bell Bowl soil found plants including prickly pear cactus, which is rare in the area.

The loss in the battle over Bell Bowl was a major blow for environmentalists, who had argued that there was a way to meet the airport’s needs without sending a road through a high-quality 5-acre section of the land, one of the last remaining places in Illinois where prairie exists much as it did 8,000 years ago. Bell Bowl is home to uncommon plants, and a foraging ground for the federally endangered rusty patched bumblebee.

The airport, which owns the 16-acre prairie, sought the road as part of a $50 million cargo expansion project.

Environmentalists sued to stop construction, rallied people throughout the state and organized protests. They said the airport could avoid disturbing the 5 acres of pristine prairie and minimize disruption of the entire prairie by moving a 1 million-square-foot cargo building east, and switching to an eastern or southeastern road location.

[ Endangered bumblebee is blocking Rockford airport expansion that will destroy rare prairie — but only for another week ]

But in March the Federal Aviation Administration approved a plan to send a road through a section of the prairie. The FAA calculated that the road would affect 9.3 acres of the 15.5 acres of remaining prairie, including 1.67 acres of high-quality prairie.

“Lots of things were lost,” said Amy Doll, director of Friends of Illinois Nature Preserves.

“We don’t know yet what is saved (by the soil relocation project), but the prairie itself is more than just the soil. It was the makeup of the bacteria, the microbiota and the insects and all the things that were living in it. We don’t know what successfully survived the move,” Doll said.

Rockford International Airport officials did not respond to a request for comment.

What’s clear, Doll said, is that the recovered soil will need volunteers to monitor growth and remove invasive plants.

She’s hoping that people who advocated for Bell Bowl during the long fight over the road will join the next step. People who are interested — or just want to see the soil relocation project — can attend a Sunday open house hosted by Friends of Illinois Nature Preserves and the Forest Preserves of Winnebago County. Held from 9 a.m. to noon at Cedar Cliff Forest Preserve, the event will include a chance to walk the site, document the presence of local wildlife and learn about volunteer stewardship opportunities.

“Bell Bowl is a great example of how our remnant natural areas can be destroyed by a bulldozer,” Doll said.

“But it’s not our only at-risk natural area in the state, because many of them are being destroyed more slowly — but destroyed nonetheless — by invasive species and people not taking care of them. They don’t have a community of people who gather on a regular basis to remove invasives.”

nschoenberg@chicagotribune.com