The Central Plains region of Canada encompasses much of the land area of the Prairie Provinces, from the central and western portions of southern Manitoba, to the lower half of Saskatchewan, to most of Alberta, and a small part of northeastern British Columbia. The total area is about 114.9 million hectares, or 12 per cent of Canada's landmass (State of Canada's Environment 1996). The region is divided into two zones: the prairie ecozone to the south, composed mostly of agricultural cropland and grasslands; and the forested boreal plains ecozone to the north. The two ecozones converge in a unique transition zone, consisting mostly of aspen parkland, where the southern prairie gradually gives way to tree cover. The region was glaciated until 10,000-15,000 years ago, leaving glacial till soils overlain by organic deposits that formed under a grass and tree vegetative complex.

The Prairie Pothole Region of Canada

Retreating glaciers left about 10 million depressions, or prairie potholes, in an area known as the Prarie Pothole Region of Canada that includes the prairie ecozone and parts of the boreal plains ecozone. As a result, complexes of wetlands with varying degrees of water permanence developed in low areas as runoff from precipitation occurred. Human settlement of the pothole region began in the late 19th century, and while it was mostly completed by the mid-20th century, some areas (e.g., northwestern Alberta) were still being settled in the 1970s. Increasingly intensive agriculture occurred with settlement, and significant changes came about in land use and land cover. Land use in the region is mostly grain farming and cattle ranching. Since the advent of intensive agriculture, the construction of drainage systems has substantially reduced the number of depressions that retain water and increased the rate at which runoff reaches river systems. In many areas, most runoff flows through wetlands with short retention time and limited groundwater recharge. This drainage system has resulted in the loss of up to 50 per cent of pristine wetlands (Ducks Unlimited, 1990). Yet much wetland area remains, interspersed with extensive grasslands.

The Prairie Ecozone

The prairie ecozone consists of a flat to gently rolling landscape underlain by deep glacial deposits. Before European settlement, the ecozone consisted largely of dry mixed grasslands in southeastern Alberta and southwestern Saskatchewan, and tallgrass prairie in the southeastern prairies of Manitoba. Since settlement, the ecozone has become one of the most extensive agricultural regions in the world. Of its total land area of 47 million hectares, 70 per cent is classified as cropland and 27 per cent as rangeland and pasture (State of Canada's Environment, 1996).

Depending on weather conditions, the ecozone can contain between 2 and 7 million wetlands. The greatest number of wetlands occurs along the subhumid northern grasslands and adjacent aspen parkland, where 25-50 per cent of the land surface is wetlands. Many former wetland areas have been converted to agricultural production. For example, in the mixed-grass prairie of southwestern Manitoba, wetland drainage and degradation and grassland conversion have been extensive. According to Zittlau (1979), almost 900,000 hectares of this area were affected by drainage between 1890 and 1935. Kiel et al. (1972) suggest that further incremental drainage continued through the 1960s. Drainage was also prevalent during the dry 1980s, and Caswell and Shuster (1992) note that 10-45 per cent of remaining basins are affected annually, primarily by agriculture. Current threats include continued agricultural and urban expansion (Ducks Unlimited, 1990).

The Parkland Region

In the transition zone that divides the prairies and boreal plains ecozones, prairie grasslands give way gradually to a more forested terrain. The southern portion of this zone is called the parklands, where the natural vegetation is grassland interspersed with aspen and oak bluffs. Only portions of this prairie and forest mosaic remain, as much of the landscape has been cultivated for agriculture or harvested by the forest industry.

Thousands of shallow ponds, or sloughs, dot the parkland landscape. However, grain farming has caused significant wetland loss and degradation in the parklands. In an effort to maximize production, the agricultural industry (via individual and government actions) drained and filled millions of wetlands. The North American Waterfowl Management Plan (NAWMP) estimates the loss of pristine wetlands at 40 per cent while Lynch-Stewart et al. (1993) estimate a number closer to 50 per cent. Turner et al. (1987) report that in the prairie pothole region many, if not most, of the remaining wetlands are now affected in some manner by haying, burning, brushing, filling and grazing. Drainage has directly caused reductions or, in some areas, almost complete loss of shallow temporary wetlands and larger permanent basins.