Partaking Partly of Each, The Surface and Subsurface of the Karst Region of Illinois

Within the Ozark Natural Division in Illinois lies a karst region, a terrain formed by the action of water, with an acidic property, in the dissolution of limestone or other carbonate bedrock layers. Often called the sinkhole plain, this karst region is dotted by topographic depressions or basins resulting from the collapse of surface soil layers into cavities which have formed underground. Within this karst region caves are an important part of the hydrologic cycle, serving as subsurface pathways that allow the movement of groundwater and rainwater and snowmelt.

Early land surveyors, describing this karst region before settlement, wrote “rolling, broken saseimensa [barrens] with sinkholes, undergrowth oak shrub and grapes, timber scattering, thin oak land.” A description written in 1836 describes the area as “neither timber land nor prairie, but partaking partly of each, and lying between them.”

Recognizing the need to preserve and restore the natural communities of this karst region in southwestern Illinois, the Illinois Department of Natural Resources manages the Illinois Caverns State Natural Area (SNA) .

The post-oak barrens, which characterizes the Illinois Caverns SNA, reveals habitat variations which allow for great biodiversity. Significant botanical components are woody species that can survive the onslaughts of intense prairie fires and enduring grasses which hold their ground against encroaching woody species. Nurtured within the barrens are various animals ranging from the tree-dependent animals, such as eastern gray squirrels which feast upon the post-oak trees’ acorns, to grass-utilizing herbivores, such as white-tailed deer which graze upon the bluestem grasses. Also thriving are wetland inhabitants which require standing water for reproduction, such as smallmouth salamanders, as well as mesic land dwellers that nest on the ground, including bobwhite quail and eastern wild turkey.

A summertime tour of the restored prairie segments at the Illinois Caverns SNA will offer the visitor an array of colors. Displaying the blue end of the spectrum may be the blooms of Ohio spiderwort (Tradescantia ohiensis), blazing star (Liatris pycnostachya) or purple coneflower (Echinacea purpurea). Exhibiting the yellows and oranges might be butterfly milkweed (Asclepias tuberosa), black-eyed Susan (Rudbeckia hirta) or sand coreopsis (Coreopsis lanceolata). Perhaps gathering nectar among the native prairie wildflowers will be a small bluish butterfly, the eastern tailed blue (Cupido comyntas), or perhaps orangish ones, such as a great spangled fritillary (Speyeria cybele) and the monarch (Danaus plexippus). In nearly luminous yellow and black plumage, a male American goldfinch (Spinus tristis) may be feeding upon the seeds of coreopsis. Tucked amongst the prairie grasses, green and growing or amongst the golden and tan senesced grass stems, the Henslow’s sparrow (Passerherbulus henslowii) may appear with its body feathered in brown and head in dark-streaked green.

A visitor will observe oak-dominated tree groves interspersed among the prairie and often growing around and within sinkholes. Perhaps an abrupt harsh, single noted whistle will reach a visitor’s ears and he or she will surmise that the vociferous bird is a yellow-breasted chat (Icteria virens). Among the tree’s foliage may be a tasty morsel (to a bird), a spicebush swallowtail caterpillar (Papilio troilus). However, the caterpillar, looking much like a bird’s droppings, may go undetected by the bird and the visitor.

Within a shady limestone crevice or near a sinkhole may be the brightly striped, jet-black western ribbon snake (Thamnophis proximus proximus) or a brown-patterned eastern copperhead (Agkistrodon contortrix), avoiding the extreme heat of summer or lying in wait for prey. Above a sinkhole pond might fly a green female eastern pondhawk dragonfly (Erythemis simplicicollis).

During the summertime a likely place found most tempting to people visiting Illinois Caverns SNA is the cave. Beneath the bright colorful and sometimes hot world of the surface lies the dark, moist, cool world of the underground where the temperature is 58° F and the humidity and darkness are nearly 100 percent. In the twilight near the cave’s entrance and even in the underground sunless world, natural communities thrive. The first link of the food chain is organic material that enters the cave. Leaves and twigs may be carried into the cave by run-off. Visiting animals, such as bats, raccoons, mice, snakes and salamanders, leave behind scat and guano (feces) and corpses; such materials provide nutrients for species that feed directly on the detritus or which forage upon the bacteria and fungi growing upon such. The foragers, such as bristletails, beetles, and millipedes become food for spiders and other predatory animals. Among the diverse fauna that have been observed within the cave are flies, snails, cave crickets, fleas, braconid wasps, staphylinid and carabid beetles, springtails and diplurans. The cave salamander (Eurycea lucifuga), a slender bright reddish orange troglophile feeds chiefly on arthropods. The adult and transforming cave salamanders can be found together in rimstone pools and potholes upon the cave floor. Two aquatic crustaceans common to Illinois Caverns SNA are the amphipod (Gammarus acherondytes) and isopod (Caecidotea brevicauda), both being only about 0.2 inches in length with numerous appendages serving sensory, maneuvering and food-handling functions. Their exoskeletons are flexible and permeable, yet tough and insoluble to the acidic water of the cave.

Bats, such as the little brown bat (Myotis lucifugus), enter the cave to roost, hanging upside down on the cave’s ceiling. In winter, various species of bats hibernate with the cave of the state natural area. In spring and summer large rooms in the cave offer suitable accommodations for bats of certain species to bear young and establish maternity colonies.

The moist, shaded exposed rock of the crevice that serves as the cave’s entrance is a unique habitat where ferns, mosses and liverworts may grow and birds, such as the eastern phoebe (Sayornis phoebe), may nest. Here the air currents of the cave respond to changes in the surface’s varying barometric pressures and temperatures. Resulting patterns of air flow cause conditions to which wildlife must adapt.

“Illinois Caverns is the only wild cave in the state open to the public,” stated Brian Jones, a Natural Resources Coordinator with the Illinois Department of Natural Resources (IDNR). Jones comments that visitors share a level of respect and humility for the cave. “Seeing visitors take pride in the unique natural wonders by adhering to safe caving practices, taking the initiative to remove litter found or to report damage observed assures me that this subterranean treasure will be preserved,” added Jones.

The largest cave system in Illinois is Fogelpole Cave, some of which lies beneath lands owned by IDNR and the Illinois Audubon Society. The Paul Wightman Subterranean Nature Preserve, owned by Clifftop Alliance, is also perched above the cave. Here native vegetation has been restored to create the prairie/savannah (barrens) ecological system, thereby helping to sustain wildlife diversity and to protect groundwater quality. This nature preserve offers parking areas and hiking trails for public access. A gate across Fogelpole Cave’s main entrance has been installed in recognition of the fragility of the cave’s natural communities in which exist threatened and endangered species. Also, the gate stands to protect the public, yet it allows ready access to bats and other wild creatures who go about their lives partaking partly of each, surface and subsurface.

Note: This article reflects, but is not limited to, the author’s original written contributions to Guide to the Illinois Caverns State Natural Area, GeoScience Education Series 19 (Samuel V. Panno, et al.).

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For years, Patty Gillespie shared her enthusiasm for language and nature and got paid for it at a public school and at a nature center. Now she plays outdoors as often as she can and writes for the sheer joy of it.