Of all the wetland types, fens are probably the least familiar to the public. This wetland community contains peat deposits (partly decayed plant material) and calcareous (calcium carbonate containing) water seepage. Fens are usually sloped, often occurring on hillsides where seepage and springs run from the ground. Found exclusively in the northern third of the state, fens may be covered by trees and shrubs or may be dominated by herbaceous wetland communities such as sedge meadows and marshes. In Illinois, and across the United States, fens are among the rarest of wetland communities, thereby emphasizing the value of their potential restoration. Wetland restoration, in general, is of particular importance in Illinois, where over 90% of our original wetland acreage has already been lost. In northeastern Illinois, specifically, urban sprawl and development pressures of the Chicago metropolitan area are especially great.
Hickory Grove Fen in McHenry County.
Hickory Grove Fen, a partially drained fen located in McHenry County in northeastern Illinois, has been studied by researchers from the Illinois Natural History Survey and the Illinois State Geological Survey for several years. For many years, much of this fen had been drained by underground field tiles and above-ground ditches. Drained areas of the fen were covered with nonwetland vegetation, including thick growths of trees and shrubs, where herbaceous fen, marsh, and wet prairie plant species formerly dominated. At the suggestion of McHenry County Conservation District personnel and with funding from the Illinois Department of Transportation, a study was initiated to determine if drainage effects could be reversed, with the goal of restoring wetland hydrology and habitat.
Restoration efforts were conducted in 1996 and 1997 with the removal of drainage tiles, filling of ditches, and removal of most woody vegetation. Water levels within some areas of the fen responded almost immediately, rising significantly. In fact, water level increases in portions of the restored fen were sufficient to satisfy the wetland hydrology criterion for jurisdictional wetlands. Water levels and ground-water discharge may yet increase in the near future. Compaction of the peat soils, resulting from years of drainage, may have slowed the restoration of wetland hydrology in some areas.
Small fringed gentian (Gentainopsis procera).
Plant community restoration and development is also expected to continue with time. Covered with thickets of buckthorn (Rhamnus spp.) and honeysuckle (Lonicera spp.) prior to restoration, plant communities have since made significant improvement. Although hydrologic restoration and plant community development are still in progress, vegetation characteristic of a calcareous fen appears to be returning. In many areas where wetland hydrology has been restored, dominant hydrophytic vegetation typical of fen, marsh, wet prairie, and sedge meadow habitats now prevails. Wetland asters (Aster simplex and A. puniceus), bulrushes (Scirpus spp.), sedges (Carex spp.), Joe-Pye weed (Eupatorium maculatum), bugle weed (Lycopus spp.), and jewelweed (Impatiens spp.) commonly dominate these wet areas. Rare, high-quality wetland species typical of fen habitat, such as grass of Parnassus (Parnassia glauca), small fringed gentian (Gentianopsis procera), and Kalm's lobelia (Lobelia kalmii), also occur regularly. Vegetation and hydrologic monitoring will continue to document in the foreseeable future further possible hydrologic recovery. A corresponding development of existing plant communities should also occur, hopefully climaxing in a fully functional, high-quality fen community, a very rare Illinois habitat indeed.
Brian Wilm, Center for Wildlife Ecology
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