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Northern Prairie Wildlife Research Center

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Wildlife Habitat Management on the
Northern Prairie Landscape

The Prairie Pothole Region


We focus on the Prairie Pothole Region of the United States (Fig. 1), although the majority of the region lies within Canada (Adams, 1988). The region is, or was, characterized by native grasslands and an abundance of wetlands situated in small depressions of glacial origin. Bounds of the region have not been precisely defined, but most authors have used or modified the bounds established by Mann (1974) as illustrated in Van der Valk (1989). Kantrud et al. (1989) presented more precise bounds for the region in North and South Dakota, based on geologic landform and density of wetland basins.

Prarie Pothole Region
Fig. 1.  The Prairie Pothole Region of North America (after Mann, 1974).

Understanding two characteristics of the region, spatial heterogeneity and temporal instability, is essential to sound habitat management. Actions that do not address the questions of where and when, as well as what and why, may yield disappointing results. Glaciation resulted in a collage of landscape features. At a distance, the most obvious features are glacial lake beds, till plains, and moraines (Stewart, 1975; Kantrud et al., 1989). Viewed from close up, even these features are highly heterogeneous. For example, the Missouri Coteau, a large morainal belt, contains various types of moraines, glacial outwash plains, and small lake beds, each possessing different topography, soil types, and vegetation. Temporally, the climate of the Prairie Pothole Region is characterized by instability and extremes. Droughts recur frequently and cause cyclic changes in the flora and fauna of the region. Also, there is a gradient in annual precipitation from wet in the east to dry in the west (Winter, 1989, pp. 24-28). Associated with this variation is a gradient in plant communities from bluestem prairie in the east, through the mixed prairie of wheatgrass, bluestem, and needlegrass, to wheatgrass and needlegrass in the west (Küchler, 1964).

Plant communities of the region, especially those in wetlands, have always been unstable. Cyclic weather patterns, grazing by huge herds of bison and other ungulates, and fires were integral to the landscape. Settlement of the region by Europeans resulted in massive changes to the prairie landscape. Tillage of natural grasslands not only caused the loss of much of the original prairie but fragmented the remaining grassland into small blocks surrounded by cropland. Free-ranging bison were nearly extirpated from the region and replaced by cattle. Eurasian plant species were introduced on purpose or by accident, and subsequently invaded the native grassland communities. Wildfires, essential to maintaining native plant communities, were suppressed, which allowed invasion of the region by woody species. Droughts in the 1930s brought extreme soil erosion to the denuded lands. In response to the erosion problem, windbreaks were planted. Woody species introduced in these windbreaks, as well as around farmsteads, small towns, and cities, further changed and fragmented the landscape of the region.

Wetland ecosystems also were substantially altered. Many of the potholes were drained to create new lands for agriculture and to increase the efficiency of tillage operations. In Iowa and southern Minnesota, nearly all of the original wetlands were eliminated (Mann, 1974). From the 1780s to the 1980s, about 42%, 50%, 35%, and 26% of wetlands were lost in the states of Minnesota, North Dakota, South Dakota, and Montana, respectively (Dahl, 1992). Further, dams were constructed on most of the major river systems, inundating the natural riverine and riparian habitats.

Along with these habitat alterations came profound changes in the community of predators; this story has been nicely summarized by Sargeant et al. (1993). Before settlement, the top predators throughout most of the region were gray wolves (Canis lupus) and occasional grizzly bears (Ursus arctos). Populations of coyotes (Canis latrans) and red foxes (Vulpes vulpes) were low, while those of swift foxes (Vulpes velox) were high. The primary prey for wolves and bears were bison and other large ungulates.

Early settlers were intolerant of wolves and, by the early 1900s, virtually eliminated them from much of the region. In the absence of wolves, coyotes greatly increased in number. The favored natural prey of coyotes includes deer and smaller mammals. Coyotes also became targets of human dislike and were aggressively persecuted by hunting, trapping, and poisoning. When they were reduced, especially in the eastern part of the area, the numbers of red foxes began to explode. Among the preferred prey of foxes are ducks, especially nesting females, and their eggs. Predation by red foxes on ducks and other large ground-nesting birds is often severe; Sargeant and Raveling (1992) estimated that foxes take about 800,000 adult ducks in the Prairie Pothole Region during a typical breeding season.

Currently, restrictions on the use of poisons and aerial hunting—along with low fur prices, which reduces trapping pressure—are causing the numbers of coyotes to increase again, especially in the US portion of the region. This change is depressing densities of red foxes (A.B. Sargeant, US Fish and Wildlife Service, personal communication, 1992). Like so many other features of the prairie landscape, predator communities are dynamic and change in response to natural and, especially, human actions.

Because the Prairie Pothole Region can produce as much as 50% of the continental waterfowl population ( Smith et al., 1964; Crissey, 1969) and host even more during migration, programs were designed to protect these birds and their habitats. Accordingly, wildlife refuges were established throughout the Region. Habitats protected by these refuges, however, are not typical of those in the Prairie Pothole Region. Rather, they usually contain one or more large lakes (often created by river impoundments), surrounded by various amounts of upland habitat.

Precipitous declines in waterfowl populations and continued loss of wetland habitat prompted the US Fish and Wildlife Service to initiate its Small Wetlands Acquisition Program in 1962 (Sidle, 1983). Under that program, the Service purchased wetlands and, more extensively, acquired easements that prevented landowners from draining, filling, or burning wetlands within easement tracts. Most tracts owned in fee title are small, often appearing as islands of grassland and wetland in a sea of tilled land. Although these programs have been effective in preserving some of the wetland base, rarely have they maintained the integrity of the original prairie ecosystem.

Declining commodity prices owing to overproduction and an alarming loss of soil prompted the initiation of a number of programs designed to convert cropland to grass and legume cover over the past four decades. The Soil Bank Program, initiated in the 1950s, converted vast areas from cropland to grassland, but by the late 1960s these lands were returned to cultivation. The Water Bank Program of the 1970s restored grassland to some cropped areas. More recently, the Conservation Reserve Program has been successful in converting cropland to grassland on highly erodible soils.

In summary, natural variability and changing priorities for land management have created a mosaic of habitat types, each of which is in constant flux. It is impossible to return to the landscape that was present in pre-settlement times. Some species have been extirpated, certain habitats eliminated, and wetland hydrology irreversibly altered. The Prairie Pothole Region, although sparsely populated, is one of the most intensively managed landscapes in North America. It will remain so despite talk of the Buffalo Commons. The challenge for wildlife agencies is to manage those parts of the system they control and to influence management on those parts outside their jurisdiction. A landscape perspective facilitates this approach.


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