Atwood Ridge Research Natural Area

[photo:] Atwood Ridge RNA. Photo by Lucy Tyrrell, USDA Froest Service.

The Atwood Ridge RNA contains several relatively undisturbed natural community types, including: barrens, hill prairie, dry upland forest, dry-mesic upland forest, and mesic upland forest. The RNA also contains two Illinois Endangered plants (including panic grass (Panicum ravenelii)), and an Illinois Threatened plant species, the chestnut oak (Quercus prinus). Several other uncommon and relict plants occur here as well, including the Cucumber-tree (Magnolia acuminata) and the rosebud-azalea (Rhododendrom prinophyllum), both southeastern species at the northwestern edge of their range. The Federally endangered American bald eagle (Haliaeetus leucocephalus) is often seen in the area during the winter.

Ecological Information

Physical and Climatic Conditions

Nearest weather station, with distance and direction from RNA:
Climatological information is taken from the collection station at Anna, which is located 4.5 miles (7.2 km) to the southwest of the RNA.
Annual precipitation (type, seasonal distribution) :
Total annual precipitation is 46 inches (116.8 cm), 54 % of which falls in April through September. Average seasonal snowfall is 13 inches (33.02 cm).
Maximum and minimum temperatures:
Average summer temperature is 77ºF, and the average daily maximum temperature is 88ºF. Average winter temperature is 36ºF, and average daily minimum temperature is 27ºF.
The base of the Mississippi Valley bluff is at 340 feet (103.6 m), while the ridge is above 600 feet (182.9 m) its entire length, and above 800 feet (243.8 m) in four segments.
Geology and Soils:
Atwood Ridge forms part of the Mississippi Valley wall. It is an unbroken, but undulating ridge with its south end lying immediately above an abandoned meander of the Mississippi River. Closely-spaced and steep-sided canyons extend from the floodplain up to the crest. Ridge crests are capped with silty loess over Devonian siliceous limestone (Bailey Formation) and chert (Grassy Knob Formation). The entire area is dissected into narrow V-shaped valleys and narrow-crested ridges. Many slopes are scree-covered. The soils over most of the area are of the Goss-Alford complex.
Aquatic Features:
Although the drainage pattern is grossly reticulate, each lateral valley has a dendritic tributary pattern. Atwood Ridge is part of the Clear Creek-Horseshoe Lake watershed. The largest stream in the area is Clear Creek Ditch.

Ecological Classification & Inventory

Ozark Highlands (222 A)
Illinois Ozarks (222Aq)
Plant Communities:
Quercus prinus, Quercus velutina, Sassafras albidum, Carya spp.
SAF Cover Types (list acres): Kuchler Types (list acres):
40 Post oak-blackjack oak (275) 91 oak-hickory forest (775)
44 Chestnut oak (200) 93 beech-maple forest (180)
52 White oak-black oak-northern red oak (300)  
60 Beech-sugar maple (180)  

View or download complete Vascular Plants List (pdf)

Common Shrub Species:
Redbud (Cercis canadensis), flowering dogwood (Cornus florida), spicebush (Lindera benzoin), common poison ivy (Toxicodendron radicans), rosebud-azalea (Rhododendron prinophyllum), pawpaw (Asimina triloba).
Common Herbaceous Species:
Little bluestem (Schizachyrium scoparium), Canada wild rye (Elymus canadensis), panic grass (Panicum anceps), divaricate sunflower (Helianthus divaricatus), prairie rosin-weed (Silphium integrifolium), basal-leaved rosin-weed (Silphium. terebinthinaceum), Virginia lespedeza (Lespedeza virginica), Trillium sp., Viola sp., Dutchman’s breeches (Dicentra cucullaria), Christmas-fern (Polystichum acrostichoides), bracken fern (Pteridium aquilinum), walking fern (Asplenium rhizophyllum).
Common Mammal Species:
White-tailed deer (Odocoileus virginianus), coyote (Canis latran), gray wolf (Canis lupus), raccoon (Procyon lotor), Virginia opossum (Didelphis virginiana), gray squirrel (Sciurus carolinensis), bobcat (Felis rufus).
Common Bird Species:
American bald eagle (Haliaeetus leucocephalus), pileated woodpecker (Dryocopus, pileatus), common turkey (Meleagris gallopavo).

Related Reports and Publications

Gates, R.J. 1995. Wood duck population and habitat investigation. Study No. 1: Population monitoring and habitat relationships of Wood ducks in southern Illinois. Final Report W-121-R. Southern Illinois University at Carbondale, Cooperative Wildlife Research Lab.

Hutchinson, Max D. 1988. Establishment record for the Atwood Ridge Research Natural Area within the Shawnee National Forest, Union County, Illinois. (pdf) Unpublished report on file at the Northern Research Station, Rhinelander, and the Shawnee Supervisor's office, Harrisburg, IL. 71 pages with appendices.

McCoy, R.A. 1997. Vegetation Analysis and Effects of Controlled Fire at Atwood Ridge Research Natural Area Union County, Illinois. M.S. Thesis, Department of Plant Biology, Southern Illinois University at Carbondale.

Sewell, Matthew. 2003. Biosystematics of the Phacelia ranunculacea complex (Hydrophyllaceae). A thesis submitted to the faculty of Miami University, Oxford, Illinois. 59 pp.

Sewell, Matthew, M.A. Vincent. 2006. Biosystematics of the Phacelia ranunculacea complex (Hydrophyllacea). Castanea 71: 192-209.

Last Modified: April 29, 2021