View of Oakwood Bottoms. Photo by Michael Jeffords.
Oakwood Bottoms Greentree Reservoir, located in Jackson County northeast of Grand Tower, Illinois, is part of Shawnee National Forest. The site, which lies in the Mississippi River and Big Muddy River floodplains, was drained by a series of channels and intensively farmed until acquisition by the federal government as part of the national forest. The land came under federal ownership in the 1930s and has been managed since 1964 as a public hunting facility and a timber resource management site.
The reservoir site is flooded during the fall and drained before the onset of the growing season. Because the Big Muddy River levee prevents natural flooding of this site, flooding is accomplished by pumping well water. As a result of tight soils and little drainage relief, the area is primarily a wet forest.
In 1976, P.M. Thomson and R.C. Anderson published an ecological investigation of Oakwood Bottoms. Pin oak (Quercus palustris), as described by Thomson and Anderson, is the dominant tree species over most of the area. They also recognized five forest community types in Oakwood Bottoms: shagbark hickory, pin oak, black willow, pin oak-cherrybark oak, and pin oak-red maple.
View of Oakwood Bottoms. Photo by Michael Jeffords.
Today, personnel at Shawnee National Forest are conducting intense studies of the forest and carefully recording populations in an effort to better manage the natural diversity of the forest. They have also made a strong commitment to the preservation of threatened and endangered species. As part of this project, the author searched Oakwood Bottoms a total of 24 days between April and November 1993 in an attempt to voucher each species of vascular plant. A total of 511 taxa were collected representing 278 genera and 90 families. The Oakwood Bottoms collection is deposited in the herbarium at the Illinois Natural History Survey.
In the Oakwood Bottoms collection, dicots are best represented, followed by the monocots, ferns and fern allies, and gymnosperms. The grass family (Poaceae) and the aster family (Asteraceae) comprise 24% of all genera and 25% of all taxa within Oakwood Bottoms. Sedge (Carex) is by far the largest genus with 34 taxa and it is the primary reason the sedge family (Cyperaceae), with only five genera, is the third largest family of vascular plants (according to total taxa) in Oakwood Bottoms. Also, the grass family and the sedge family together comprise 63% of the monocot genera and 78% of the monocot species.
Despite the heavy impact of farming and drainage control (channels and levees), Oakwood Bottoms has retained an interesting and diverse flora. Three state endangered species, all perennial herbs, were collected: finger dog-shade (Cynosciadium digitatum), Arkansas manna-grass (Glyceria arkansana), and pole manna-grass (Puccinellia pallida). Finger dog-shade was first collected in Illinois in Oakwood Bottoms in 1969. It has not been found elsewhere in the state and this rediscovery of finger dog-shade in Oakwood Bottoms is the first verification of its persistence at this site. Between 1,000 and 2,000 plants were observed during this study, all in the southern portion of Oakwood Bottoms. Arkansas manna-grass and pole manna-grass were both previously known only from Union County in a floodplain swamp along the Big Muddy River. About 50 plants of Arkansas manna-grass in one population were found in the southwest portion of Oakwood Bottoms and three populations totaling about 200 plants were found in the northern part of Oakwood Bottoms.
Swamp red iris (Iris fulva) found in Oakwood Bottoms. Photo by Ken Robertson.
Two species discovered in Oakwood Bottoms, not commonly found in their respective ranges, include Wolf's sedge (Eleocharis wolfii) and lake cress (Armoracia aquatica). Wolf's sedge is currently designated by the U.S. Fish and Wildlife Service as a "candidate under review" for inclusion in its list of endangered and threatened species. Hundreds of plants of Wolf's sedge were found in Oakwood Bottoms. Six plants of lake cress were found in one population in Oakwood Bottoms. Two species, swamp red iris (Iris fulva) and mock bishop's weed (Ptilmnium costatum), which had been listed previously as Illinois endangered and threatened species, were found scattered throughout Oakwood Bottoms. A few additional infrequently encountered plants for southern Illinois were found in various locations within Oakwood Bottoms. They include hornwort (Ceratophyllum echinatum), manna-grass (Glyceria septentrionalis), marsh vetchling (Lathyrus palustris), smooth-flowered muhly (Muhlenbergia glabriflorus), unusual fescue (Festuca paradoxa), and water purslane (Didiplis diandra).
Data from the current completed study has been forwarded to the U.S. Forest Service. This information will provide a baseline against which the Service can compare future inventories as it continues to monitor and study Oakwood Bottoms. Without a thorough inventory it has not been possible to gauge the effects of agriculture on the florisitc diversity of the Bottoms. Such trends will now be possible to discern using data collected in this study.
Loy R. Phillippe, Center for Biodiversity
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