At Grainger Woods, mesic oak woodlands, wetlands, meadows and prairies harbor several state-listed threatened and endangered species including a sedge not seen in the Chicago region since 1955. The site’s rare northern flatwoods contain mainly swamp white oaks, black ash, musclewood and hop hornbeam. Seasonally flooded woods, flatwoods are wet in the spring and fall and dry during summer. The site also features a large formerly-grazed pasture that is slowly returning to its original prairie state as evident by emerging native plants including prairie dock, golden ragwort, blue-eyed grass, large yellow fox sedge, crested oval sedge, wild strawberry and other plant species.
Several grassland birds have found excellent habitat in the abundant pasture grasses. The bobolink, meadowlark, Eastern kingbird and the savanna sparrow were spotted on the site by forest preserve staff, and a voice identification was made of the state-threatened Henslow’s sparrow.
The Illinois Department of Natural Resources has designated a 169-acre portion in the southwestern part of Grainger Woods as an Illinois Nature Preserve, a status conferred only on the state’s most ecologically sensitive public lands. The designation will provide protection to seven state endangered or threatened species. The portion of the site named as an Illinois Nature Preserve contains wet-mesic upland forest, and northern flatwoods, which is a globally imperiled community. The designation will provide protection to seven state endangered or threatened species.