Because of a new St. Croix River bridge, an 8,000-year-old purple prairie plant will be saved from possible extinction in western Wisconsin.

The dotted blazing star, native to the region long before human feet arrived, is a "remnant" from an earlier, post-Ice Age era. It's classified as an endangered species in Wisconsin, and that's why the rescue of 54 plants from the bridge's path stirs promise for their longterm survival.

"These are heirloom plants, really endemic to this area. We're just trying to protect them and increase them," said Harvey Halvorsen, area wildlife supervisor for the Wisconsin Department of Natural Resources. "The significance is that we have within our hands an opportunity to not lose this plant in the state of Wisconsin. It recognizes our heritage."

In October, ecologists excavated a patch of dotted blazing stars from an area just east of the forthcoming bridge that will be plowed under for a connecting highway. The 54 plants, carefully removed for preservation, were taken to nurseries in Baldwin and Hayward and a seed farm near New Richmond, where they will be nurtured into hundreds and eventually thousands of new plants.

"We rescued them out of the footprint of the new structure," said Troy Stapelmann, an environmental engineer for the Wisconsin Department of Transportation. "They all would have been lost if we had not moved them. We couldn't avoid it. It happened to be right in the path where the bridge was going to go."

The butterfly-attracting plants, notable for their heads of purple flowers and slender, plume-like bristles, were growing in a ditch along Hwy. 35. Workers from several government agencies and advocacy organizations such as Prairie Enthusiasts worked together to save the plants before the two-state bridge construction begins, he said.

"We partner because we realize that a species doesn't really know political boundaries," he said. The four-lane bridge, part of a mammoth $690 million highway project, will extend from Oak Park Heights to St. Joseph Township, Wis. It will divert traffic from the Stillwater Lift Bridge when it opens in 2017.

What comes next

By late spring, dotted blazing star seedlings from the nurseries will be planted in western Wisconsin within the Western Prairie Habitat Restoration Area. That's their native territory, on the eastern edge of the Great Plains, where the plants once proliferated on far-flung prairies.

Some will be planted on the prairie near Somerset. Others will be grown in the New Richmond High School greenhouse project, in a lab on the University of Wisconsin-River Falls campus, and at a prairie plot at Houlton Elementary School not far from the new bridge.

On the Minnesota side of the river, the dotted blazing star -- individual plants have a life cycle as long as 35 years -- isn't endangered in Washington County or elsewhere, although the plant's habitat has vastly diminished.

"That's because we just have more prairie, I guess, than Wisconsin does," said Hannah Texler, regional plant ecologist for the Minnesota Department of Natural Resources. "It's not that it's common here, but relative to Wisconsin we have more."

Today, less than 1 percent of native prairie remains in Minnesota because of farming, urban growth and fewer wildfires that once kept woodlands from overtaking native prairie, she said. The dotted blazing star has been found on native prairie that remains, she said, although it's hard to measure losses because of changes to the landscape over the past century.

The bridge project will bring significant changes to St. Joseph Township, where a new highway will cut through farms and meadows. All the new construction means that conservationists pay closer attention to the welfare of plant and animal life, including butterflies, turtles, mollusks, bald eagles and bluebirds, Halvorsen said.

"The development pressure in St. Croix County and Polk County is going to explode, and that's going to mean more wildlife habitat being parceled and fragmented," he said. "It will impact deer and deer movements. We'll have more people hunting, visiting, bird watching on public land. Our job is to harmonize."

Kevin Giles • 651-925-5037 Twitter: @stribgiles