SPRING GREEN, Wis. — The Wisconsin River roiled and churned and licked at its banks as we drove across the Wisconsin 23 bridge at Spring Green.

Recent recurring mid-September rains had emboldened the river with a relentless purpose.

My son, Brian, and I were en route to the Spring Green Nature Preserve to meet up with our local hiking guide for the day, conservationist and author Curt Meine. Having gotten ourselves lost and 15 minutes late, we flew into the preserve parking lot with as much haste as the rushing river.

Curt deflected my apologies: “What, so I had to spend a few extra minutes basking in this glorious morning?”

The history

The preserve embodies both sides of this morning: The gentle swaying of prairie grasses in the early autumn sun belies its thunderous beginnings.

The preserve is a rare Midwestern sand prairie born perhaps 17,000 years ago in the waning glacial period when an ice dam holding back melt water in Glacial Lake Wisconsin suddenly burst.

The escaping waters carved out today’s Wisconsin Dells and surged down the Wisconsin River toward the Mississippi.

“It must have been an epic flood,” Curt said.

Geologists speculate the rush might have been as quick as seven days, during which it flooded the valley and filled it with 100 feet of glacially pulverized sand from the glacial lake upstream. The Spring Green Preserve showcases an 1,100-acre sandy remnant of the outwash and of the blowing winds and dunes that followed.

As Curt, Brian and I entered the prairie, a host of grasshoppers flicked across the path ahead of us. As we walked, Curt often stopped us to point out Indian grass, whorled milkweed, blazing star, big bluestem and little bluestem grasses.

The prairie sports both tallgrass and shortgrass species. Tallgrass, like big bluestem, is more prevalent in the Midwest where it thrives in the typical rich, black, soil. Here in the sand prairie it grows in the wetter lowlands.

Shortgrass, like little bluestem, is more common in the drier west. But shortgrass species, like little bluestem, are quite happy in Midwestern sand prairies, where the soil drains quickly, mimicking drier, Western conditions. Here, it begins growing where the prairie rises to meet the bluffs that loom 200 feet above the floodplain.

The Unusual

More unusual to the Midwestern eye, though, is the prickly pear cactus growing quite nicely, if low, in the Wisconsin sand. No doubt the cactus inspired the sand prairie to have been known colloquially as the Wisconsin Desert.

Curt pointed to plant variations just beyond the hiking path. Sand blowouts — temporary exposures of sand caused by winds funneling up the river valley — create micro communities where conspicuous patches of prairie cottonweed wave in the wind. Conversely, small groves of black oak dot the occasional sinks of wetter soil.

The sand prairie provides niche homes to animal species as well. The Ornate Box Turtle is so rare that conservationists track their movements with radio transmitters, making sure, for example, that the turtles are burrowed into the sand before the prairie is burned.

The prairie provides habitat for all sorts of crawling and winged critters with menacing names: Tiger beetles, wolf spiders, black widow spiders and predatory wasps. The three of us amused ourselves for a while watching two beetles waddling along with a chunk of insect. We couldn’t decide if they were ineptly trying to cooperate or if beetle No. 1 was trying to steal the prize.

For those who prefer avian wildlife, the sand prairie is home to dickcissels, grasshopper sparrows, indigo buntings, orchard orioles and many other species that nest in the grasses or stop over during migration. The preserve is a favorite location for birding enthusiasts.

“This is the place to find the lark sparrow,” a grassland bird listed as a Species of Special Concern, Curt said. “They like the open ground and patches of sand.”

Not so the sandhill crane, another rare bird found in autumn along the river.

“We’re wetland birds,” Curt says on their behalf as we watch a pair circle the rim of the prairie and disappear beyond the terrace bluff. “This place is not for us.”

The challenges

Sand prairies made for challenging agricultural conditions because they drain so quickly and are not nutrient-rich. Even so, much of this habitat has been lost. Curt points out that today’s preserve was identified early on in the 1940s for preservation by conservationist Aldo Leopold and his contemporaries.

Leopold “wanted to protect the best gems,” Curt says, and included this site due to its niche plant and animal communities.

Preservation didn’t happen overnight, however. The land was eventually purchased by the Nature Conservancy beginning in 1971, and restoration began shortly thereafter.

Prairie restoration and maintenance is labor-intensive. In the absence of prairie fire in the post-settlement era, sand prairies tended to be overtaken by red cedars. Many of the nearby bluff terraces are cedar-draped, but due to tree removal and controlled burns, the Spring Green Preserve looks more like it did in the early 1800s. Often, a burn will bring about its reseeding, Curt adds, “releasing prairie seed already in the ground.”

As we finish our sand prairie hike, Curt resituates us in the sand-rich Wisconsin River valley that resulted from the break in the ice dam holding back the waters of Glacial Lake Wisconsin. The Wisconsin River, he says, is known as the river of a thousand islands, always shifting “islands, shifting because the river floats on a bed of sand.”

“The river is a paddler’s delight because it contains no dams for 92 miles, a direct result of the deep sand, Curt said, pointing out that “it’s hard to put a dam on a sand foundation.”

After the hike and a lunch, we depart in our separate directions: Curt to his nearby home; Brian back to Chicago where he lives; and me back home to Dubuque.

I cross the rain-swelled Wisconsin River one more time and imagine its waters chasing me downstream to the Mississippi where it will crest past my hometown in a few days’ time.

As it has done through the ages.

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