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The landscape of North Dakota is largely the result of glaciation (Figure 1). When the last glaciers retreated from the region approximately 12,000 years ago, they left behind a landscape dotted with numerous depressional wetlands caused by the uneven deposition of sediments, the scouring action of glaciers, and the melting of buried ice blocks. Due to the geologically young nature of the landscape and the resulting lack of integrated drainage systems, wetlands in the prairie pothole region of North Dakota are typically not connected by overland water flows; however, they are connected to and are greatly influenced by ground-water flow paths (Winter and Rosenberry 1995). The unique hydrology and climate of this region have a profound influence on the hydroperiod, water chemistry, and ultimately the biotic communities that inhabit these prairie wetlands (Kantrud et al. 1989, Euliss et al. 1999). Stewart and Kantrud (1971) developed a wetland classification system based on these differences in plant communities resulting from various hydrologic regimes and water chemistries (i.e., salinities), and Kantrud et al. (1989) provide lists of plant species associated with the different water regimes and salinity levels of prairie wetlands.

Figure 1.  Location of Hawk's Nest Wildlife Development Area (HN), Sweet Grass Wildlife Development Area (SG), Pilgrim's rest Wildlife Development Area (PR), and the Cottonwood Lake Study Area (CL) in the Prairie pothole region of North Dakota

In addition to hydrologic regime and salinity, disturbance by man has had great influence on plant species composition of prairie wetlands (Kantrud et al. 1989). Cultivation of wetland basins commonly occurs in short hydroperiod wetlands and even in long hydroperiod wetlands during drought years. Farmers also regularly cultivate the outer zones of many wetlands with greater water permanence. These operations can temporarily eliminate most plants in these areas and, if repeated regularly, do not allow the original native plant communities to reestablish themselves (Kantrud and Newton 1996). Further, cultivation of wetland catchments has increased sedimentation rates of prairie wetlands (Gleason and Euliss 1998). Kantrud and Newton (1996) noted silt accumulations that virtually eliminated the plant communities of the wet meadow zone in several of their study wetlands in cultivated watersheds.

In order to shorten the hydroperiod and thus increase to amount of time when wetlands are dry and can be farmed, many prairie wetlands have been drained either with open ditches or tiles. Approximately 50% of the estimated original 8 million ha of wetlands in North Dakota no longer remain (Dahl 1990). In response to increased awareness of wetland functions and values, numerous prairie wetlands have been restored in efforts to reverse the impacts of wetland drainage. However, Galatowitsch and van der Valk (1996) found that while deep marsh and submersed plant species appeared to be comparable, the number of wet meadow and sedge meadow species was lower in restored wetlands than in natural wetlands. Additionally, restored wetlands may be shallower than their natural analogues due to increased sedimentation during the time period when the wetlands were drained and farmed. This loss of wetland volume in restored wetlands may influence hydrologic regimes and water chemistry that ultimately determine plant species composition (Gleason 2001).

In July and August, 1995, we sampled the plant communities of wetlands within one natural wetland complex, the Cottonwood Lake Study Area (16 wetlands sampled), and three restored wetland complexes, Hawk's Nest Wildlife Development Area (14 wetlands sampled), Sweet Grass Wildlife Development Area (11 wetlands sampled), and Pilgrim's Rest Wildlife Development Area (12 wetlands sampled). These wetland complexes are hereafter referred to as Cottonwood Lake, Hawk's Nest, Sweet Grass, and Pilgrim's Rest. Cottonwood Lake (Section 19, T142N, R66W, Stutsman county, ND), Hawk's Nest (Section 10, T144N, R68W, Stutsman county, ND), and Sweet Grass (Section 34, T145N, R70W, Wells county, ND) are situated along the eastern portion of the Missouri Coteau in North Dakota, whereas Pilgrim's Rest (Section 34, T134N, R95W, LaMoure county, ND) is situated in the Glaciated Plains of North Dakota (Figure 1). Wetlands within the three restored wetland complexes were restored by the U.S. Bureau of Reclamation in 1987, 1990, and 1993, respectively. Thus, the restored wetlands in the complexes were eight, five, and two years old when sampled in 1995. The upland areas of all three restored complexes were reseeded to grassland cover during restoration; however, no supplemental plantings of native wetland species occurred in any of the three restored wetland complexes. The natural wetland complex evaluated, Cottonwood Lake (see http://www.npwrc.usgs.gov/clsa), is an undrained complex that has been used for long-term studies since 1967. Information on wetland hydrology, water chemistry, and biota (e.g., Winter and Carr 1980, Hanson and Swanson 1987, LaBaugh et al. 1987, Nelson and Butler 1987, Poiani and Johnson 1988, and Swanson 1990) provided reference data to facilitate comparisons with the three restored wetland complexes (Horner and Raedeke 1989, D'Avanzo 1990).