Take a walk through a dolomite prairie

_{|  Story by Meghan McMahon |}

_10/6/2023

Picture a prairie and what do you see? Acres upon acres of open grasslands with few if any trees scattered about? These prairies once dominated Illinois, but very little of the Prairie State remains prairie. However, small pockets of northern Illinois remain home to an extraordinarily rare type of prairie called dolomite prairie.

At first glance, dolomite prairies might look like an ordinary prairie. They are home to some of the same prairie plants you would find in any other prairie. Take a walk through a dolomite prairie, however, and you’ll start to notice some differences, starting with what is right below your feet.

What is dolomite?

Dolomite is a kind of bedrock, the solid rock underneath loose material like soil and gravel at the Earth’s surface. The chemical composition of dolomite is similar to that of limestone. Both dolomite and limestone contain calcium, but dolomite also contains magnesium as part of its components, said Forest Preserve natural resources manager Nick Budde.

Dolomite prairies occur only where dolomite is at the surface level, Budde said. In these prairies, the dolomite is visible in places along the prairie floor. They are different from our more traditional prairies that once dominated the Illinois landscape because they don’t have deep, rich soils that so many of our native grasses and wildflowers thrive in.

In Illinois, dolomite prairie is only found in the northern part of the state, along the upper Illinois River and some other area rivers, the Illinois Department of Natural Resources reports. Only about 140 acres of dolomite prairie remain in the state, and most dolomite prairie sites are quite small, according to a land survey conducted by the state in 1992.

In the Will County preserves, dolomite prairie occurs in the Des Plaines River Valley. The best examples of this habitat are at Lockport Prairie Nature Preserve, Lockport Prairie East Preserve and Romeoville Prairie Nature Preserve, Budde said. Pockets of dolomite prairie can also be found at Keepataw Preserve and Rock Run Preserve, as well as at Midewin National Tallgrass Prairie, which is owned and managed by the U.S. Forest Service.

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Why are dolomite prairies so rare?

In the Chicago region, the bedrock is dolomite or limestone, but in most places it is covered by many feet of soil. Dolomite is only exposed at the surface level in areas where the soil has been removed. In what are today dolomite prairies, this removal of the thick layer of soil occurred in concentrated areas, creating river valleys, thousands of years ago when Glacial Lake Chicago flooded the region.

“Dolomite prairies are rare because there are not many areas where dolomite occurs at the surface,” Budde said.

While most of Illinois’ once expansive prairies have been plowed over for farming and development, the dolomite prairies, which were never nearly as abundant, remain largely intact. Some of these rare pockets remain because the bedrock being so close to the surface makes the land unsuitable for farming and many kinds of development.

“It’s not productive for farming, and it’s not really good to develop on, but even still it’s hyper rare,” Budde said, adding that it only formed in very narrow bands created by the glacial flooding.

Rare flora and fauna

The soil in a dolomite prairie has a high magnesium content because of how the rock has been weathered over time, IDNR reports. The high magnesium content allows these areas to support many rare and unique plants that do not grow in many other locations.

In Will County and the Chicago region, two federally endangered plant species, lakeside daisy and leafy prairie clover, grow locally only in dolomite prairies, Budde said. Other plants that are unique to this rare habitat include Butler’s quillwort, which is endangered in Illinois, and Minuartia patula, which is sometimes called pitcher’s stitchwort.

Because there isn’t a lot of surrounding vegetation, plants like the lakeside daisy have to be able to tolerate harsh environments in all kinds of weather, from the bitter cold of winter to the stifling heat of summer, Budde said.

“It has to be able to sustain itself in these extremes,” he said. “They have really adapted to the harsh, exposed extremes of the climate here.”

Plants like this don’t grow in other areas because they can’t tolerate competition from other plants. ”If you put them in an area where everything can grow, they will quickly get outcompeted,” he said.

It’s not just rare plant species that are found in dolomite prairies. The Hine’s emerald dragonfly, which is federally endangered, is known to use dolomite prairie as its territory.

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And in the Will County preserves, spotted turtles, which are state endangered, are only found in dolomite prairie preserves. In fact, most of the spotted turtles in Illinois can be found in Will County preserves, Budde said.

The mammals you can expect to see in a dolomite prairie might be more limited than in other habitats as well. While you may see deer, coyotes, foxes and the like, you won’t often see evidence of burrowing animals because the bedrock being so close to the soil does not offer suitable habitat, according to the Illinois State Museum.

^{(Lead image of Lockport Prairie Nature Preserve by Glenn P. Knoblock)}