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Center for the Environment, Cornell University, 409 Wing Hall, Ithaca, NY 14853; South Dakota State University, Department of Horticulture, Forestry, Landscape and Parks, Brookings, SD 57007

A prolonged drought in central North Dakota during 1988-92 caused the quality of wetland habitat for nesting waterfowl to decline significantly. For example, many of the semipermanent prairie wetlands at the Cottonwood Lake site have become closed with emergent vegetation (e.g., Typha spp.) and contain few or no open-water areas.

In this study, a simulation model was used to estimate water depth and duration needed, either through natural or artificial means, to restore productive habitat by creating a balance between open water and emergent cover. The model is a spatially defined, rule-based simulation model of prairie wetland hydrology and vegetation dynamics. A semipermanent wetland on the Cottonwood Lake site with closed cover (P4) was chosen for the model experiments.

The effects of four water-depth classes (75, 100, 125, and 150 cm) were simulated for a five-year period. Simulations were performed with both fluctuating and constant conditions (i.e., simulations had an average water depth or constant water depth in the deepest part of the basin over a growing season). The various water-depth classes produced markedly different cover-ratios by the end of a simulation. Among the constant-depth scenarios, open water ranged from 11 to 73%, and among the fluctuating-depth scenarios, from less than 1 to 68%. Differences between constant and fluctuating conditions for the same depth class also existed. For example, a constant depth of 100 cm produced about 42% open water compared with only 17% for fluctuating conditions. Percent open water was always greater for a given depth class with constant water levels. The desired 50:50 ratio was best approximated by the 125-cm depth class with fluctuating conditions.

These results indicate that a spatially explicit model that integrates hydrology, topography, and vegetation dynamics can provide target water levels for managers to reach desired habitat characteristics either for natural or restored wetlands. Model simulations should be less expensive to conduct than field experiments; however, the current model will require further testing before becoming accepted as a reliable management tool.