Plants and Animals:
Dolomite Prairie

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Most prairies in Illinois are on thick, layers of sediment deposited by glaciers and glacial streams. However the Drummond Dolomite Prairie, located on the western edge of Midewin, occurs on thin soils overlying dolomite bedrock. Because these soils were not particularly suitable for agricultural purposes, the dolomite prairie is one of the best-preserved natural communities on the site. The dolomite, which is a calcium magnesium carbonate, lies within a meter of the surface. As a consequence, the thin overlying soils are alkaline and have a high magnesium content an important plant nutrient.

Because the bedrock impedes drainage, the soils are frequently saturated in the spring, but because the thin soils have a low water holding capacity, they dry out more quickly during dry seasons. In some places a ‘dolomite pavement’ occurs with no soil whatsoever. Drummond Dolomite Prairie contains a mix of wet, mesic, and dry prairie, which intergrade into each other.

The wet dolomite prairie includes tufted hair grass (Deschampsia caespitosa var. glauca), blue-joint grass (Calamagrostis canadensis), prairie cord grass (Spartina pectinata), and swamp milkweed (Asclepius incarnata). Riddell’s goldenrod (Solidago riddellii) occurs on soils that are less wet, along with Crawe’s sedge (Carex crawei), a threatened species in Illinois, which prefers a calcareous environment. Other Illinois endangered and threatened plants that occur in the wet to wet-mesic dolomite prairie are hairy marsh yellow cress (Rorippa islandica var. hispida) and slender sandwort (Arenaria patula). Butler’s quillwort (Isoëtes butleri), another endangered plant in Illinois, also occurs in the adjacent Des Plaines Conservation area and may occur in the wet parts of Drummond Dolomite Prairie (Glass, 1994).

Damaged Prairie dropseed
Prairie dropseed
damaged by voles or mice.
The mesic dolomite prairie at Drummond has a deeper, better-developed soil than those of the wet or dry dolomite prairies. The widespread tall-grass prairie species big bluestem (Andropogon gerardii) and Indian grass (Sorhgastrum nutans) occur on the mesic dolomite prairie. Prairie dropseed (Sporobolis heterolepis) occurs on both the mesic and the dry sites at Drummond Dolomite Prairie. Because prairie dropseed has a tussock growth form, with growing points at or slightly above the soil surface, it is less tolerant of fire and grazing than big bluestem and other prairie grasses, which have growing points below the soil surface. The basal growing point of prairie dropseed is also subject to damage by voles or mice, which nest in them.

The dry and dry mesic dolomite prairies at Midewin contain two state and federally endangered and threatened plant species, hairy false mallow (Malvastrum hispidum), and leafy prairie clover (Dalea foliosum). Other plants characteristic of the dry dolomite prairie are side-oats grama (Bouteloua curtipendula), which also exists at mesic sites, prairie dropseed, nodding wild onion (Alium cernuum), low calamint (Satureja arkansna), hairy beard-tongue (Penstemom hirsutis), and round-fruited St. John’s-wort (Hypericum sphaerocarpum).

On thin, gravelly, dry soils and on exposed dolomite pavement, only a very patchy covering of drought tolerant species occurs. Prickly pear cactus (Opuntia humifusa) and side-oats grama grass occur at such sites. Lichens and mosses grow on the exposed dolomite and the soils adjacent to it. The lichen (Catapyrenum lechneum) grows in soil pockets between the dolomitic pavement, and the lichen Dermatocarpon miniatum grows directly on exposed bedrock.

Exposed Dolomite Pavement
Midewin NTP

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Illinois State Museum State of Illinois IDNR Search, Last modified September 1st 2011, 03:13PM.