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Effects of Vegetation Manipulation on Breeding Waterfowl in Prairie Wetlands — A Literature Review

Research Needs

The prairie wetland complex has been severely degraded. Thus, it is too late to determine precisely the natural plant associations and structural types of vegetation historically preferred by waterfowl species during different phases of the breeding cycle. Other than drainage, cultivation, and siltation, the worst problem now is decreased waterfowl use caused by the regression of many of the semipermanent wetlands toward Typha spp. monotypes, and the encroachment of woody plants such as Salix spp. The problem is especially noticeable in the eastern portion of the prairie pothole region where livestock production has decreased, and many wetlands now lie idle. The problem is no less severe on much of the publicly owned land devoted to waterfowl production. In this instance, wetland managers seldom have the time, equipment, or manpower to properly manipulate vegetation on wetlands. More importantly, managers lack the information needed to obtain desirable, predictable results. However, much useful information can still be obtained by studying existing wetland complexes that are subjected to various land uses or combinations of uses.

Much remains to be learned about the physical and biological environments preferred by species of breeding waterfowl during their seasonal and daily activities. This should be ascertained from existing wetland complexes that are in the highest state of natural preservation. Knowledge of the preferred feeding, nesting, loafing, and roosting areas, and reactions and adaptations of the birds to climatic changes and predator pressure would aid in evaluating future experiments in marsh management.

Armed with a better understanding of the life history of individual species, burning and grazing treatments should be applied individually and in combination to selected prairie wetlands of various classes, salinity subclasses, vegetative types, and sizes that are most important to the common species of waterfowl.

Burning and grazing experiments should stress seasonality, frequency, and intensity, and the interactions of these variables should be measured. Effects of cover level (amount of emergent cover) should be separated, if possible, from the effects of cover configuration (size of clumps, shape of clumps, distances between clumps), as suggested by Murkin et al. (1982). The investigations should be long-term because of the drastic climatic fluctuations in the prairie pothole region. It would also be helpful if treated wetlands were dispersed over a broad geographical area to allow for differences in precipitation across the region. Studies should not be limited to the effects on waterfowl, but include the response of the vegetative community and the invertebrate food organisms of waterfowl. The response of other wetland vertebrates (primarily herbivores) to higher nutritive quality of burned wetland vegetation should also be measured as recommended by Smith et al. (1984).

Finally, changes to the physical and chemical environment should be monitored to increase our knowledge of causative factors involved in the biotic responses observed, and for the potential predictive values of abiotic factors in future marsh manipulations. Basic measurements should include winter snow accumulations, fluctuations in water depth and temperature among wetland vegetation zones, insolation, and standard water quality parameters.

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