Prairies

Grasslands occupy a vast area in North America, from the Rocky Mountains on the west to the deciduous forests on the east, and from the boreal forests in the north to the Gulf of Mexico. In Canada, mixed-grass and fescue prairie dominate these grasslands. The aspen parkland—a narrow band of grassland with scattered occurrences of aspen groves—separates these grasslands from the forests. The grasslands surround a small, geologically unique upland that has a lodgepole pine vegetation similar to that found in montane regions to the west. Thus grassland, aspen parkland, and montane forest regions constitute the Prairie Ecozone in Canada. This ecozone covers the southern one-third of Saskatchewan, approximately 24 million hectares, extending from the boundary with the United States to the Boreal Plain Ecozone.

Physiography. The Prairie Ecozone is essentially a level to gently rolling plain with numerous subdued uplands dispersed throughout most of its extent. Small but prominent uplands rise above this plain in its southern part. Elevations in the Prairie Ecozone are lowest in the northeastern part of the area. The Missouri Coteau and then the Wood Mountain and Cypress Hills plateaus represent successive increases in elevation, from approximately 1,000 m in the northeast to 1,100 m in the southwest.

Geology. glacial deposits, which represent the surficial sediment throughout the Prairie Ecozone, may be hundreds of metres thick. They are generally thinner in the Prairie Ecozone than in the Boreal Plain Ecozone, and parts of the Cypress Hills and Wood Mountains were not glaciated. As a consequence, the regional topography of today closely mirrors the shape of the bedrock surface that existed prior to Glaciation. Also, the composition of the glacial deposits is strongly influenced by the nature of this underlying bedrock. Late Cretaceous and Tertiary age rocks cover older Phanerozoic rocks throughout the Prairie Ecozone. The Tertiary rocks formed mainly in river and lake environments, whereas the Cretaceous rocks are of marine origin.

The youngest rocks of Tertiary age contain appreciable amounts of gravels and quartzites, which have resisted millions of years of geological erosion. This has maintained the surface in the Cypress Hills far above the surrounding lands, where the softer and older sands and clays have been largely or entirely removed. Geologists believe that a thickness of about 1 km of Tertiary rocks has been eroded from Saskatchewan’s landscape and that before erosion, the extent of the Tertiary deposits may have been much greater than presently known.

Glacial deposits, however, have a profound influence on the nature of the local landscape throughout the ecozone. Till plains and hummocky moraines, often with an abundance of glacial kettles, are a dominant feature of the area. Nearly level glaciolacustrine areas are also common, as are glaciofluvial areas that are often modified by wind to form dunes. Valleys and rivers cross this plain, flowing through the Beaver, North and South Saskatchewan, Red deer, Assiniboine, Qu’Appelle and Souris rivers to the Churchill and Nelson rivers and into Hudson Bay, and through the Frenchman River to the Missouri River and the Gulf of Mexico.

A dominant regional feature is the Missouri Coteau, a major northeast-facing bedrock escarpment. Many large ice-pushed ridge complexes are located along this escarpment. The Dirt Hills, south and southwest of Regina, are among the largest and best developed ice-pushed ridges in the world. The soft shale and mudstone bedrock was thrust upward by the force of the advancing glacier, so that in places bedrock overlies younger glacial deposits. Postglacial events have also impacted on Saskatchewan’s landscape. Underfit streams, with their characteristic floodplains, are active in channels that originated as meltwater channels from the ice or spillways from glacial lakes. Lakes such as those in the Qu’Appelle Valley have formed between alluvial fans that blocked the glacial valley where present-day creeks enter it. Sand dunes have been active since glaciation.

Climate. The climate in the Prairie Ecozone ranges from semiarid to humid continental, with long and cold winters, short and very warm summers, and cyclonic storms. Temperatures are highest at lower elevations in the south, progressively decreasing with increasing altitude and latitude. Precipitation is generally low, but it increases slightly from south to north and more markedly from west to east. This precipitation trend, when combined with temperature gradients described above, has created a series of climatic zones from cool semiarid in the southwest to moderately cold subhumid in the northeast. Climatic zonation also occurs in response to altitude, as moderately cold semiarid to subhumid conditions prevail on uplands in what is otherwise the driest part of the ecozone.

Landforms and Soils. Most landforms in the Prairie Ecozone are of glacial origin. Nearly level ground moraine (till plains), glaciolacustrine and glaciofluvial plains are major contributors to the “flat prairie” landscape, although glacial kettles break this monotony in some areas. Gently rolling to hilly hummocky as well as ridged moraines and sand dunes add to the diversity of the landscape. Valleys and coulees, sometimes with enclosed lakes, are often the most striking landscape features.

Soils strongly reflect climate and natural vegetation and the associated landform. Soils formed in glacial till, the sediment that constitutes ground moraine and hummocky moraine, are usually loam textured, while those formed in glaciolacustrine deposits have higher proportions of silt and clay, and those formed in glaciofluvial deposits have more sand and gravel. Chernozemic soils are synonymous with a grassland vegetation, so the entire Prairie Ecozone is dominated by them. Brown Chernozemic soils are associated with mixed grasses in the sub- to semiarid region; Dark Brown Chernozemic soils with a more productive mixed-grass vegetation in the semiarid region; and Black Chernozemic soils with a fescue prairie-aspen grove parkland vegetation in the subhumid region. Dark Gray Chernozemic soils occur in areas transitional to the boreal forest. Solonetzic soils occur in all of the soil climatic zones in association with parent materials containing a high content of sodium salts; Regosolic soils prevail on recent deposits such as alluvial flood plains and sand dunes; and Gleysolic soils prevail in wetland areas.

Groundwater. In the Prairie Ecozone, the basal aquitard of Precambrian and Paleozoic rocks is overlain by bedrock aquifers. These aquifers in turn are confined by an upper aquitard of Cretaceous shale. The Judith River and Ravenscrag aquifers are the most important of these bedrock aquifers in this ecozone. The Hatfield and Tyner valley and several other buried valleys lie on the bedrock surface and provide valuable sources of groundwater for the ecozone. Aquifers also occur within the glacial sediments, most notably within and at the surface of the Floral Formation. Surficial aquifers, representing sandy and gravelly glacial deposits, are scattered throughout the ecozone.

Vegetation. The Prairie Ecozone is a grassland region. A mixed-grass community dominates the southwestern, warmer, and more arid part of the ecozone, represented by the Mixed Grassland ecoregion. A late summer moisture deficit, caused by low precipitation and high evapotranspiration, and periods of extensive droughts typify the climate of this area. The resulting mixed-grass vegetation includes what are often referred to as “short grasses” (blue grama grass and sedge) and “mid to tall grasses” (wheatgrasses, June grass, needle-and-thread, and porcupine grass), along with pasture sage and moss phlox.

Northward and eastward from the mixed grassland, moisture deficits are less severe and droughts are less prolonged. “Mid-grasses” dominate these areas, along with an increase in the extent of shrublands, aspen grove woodlands, and wetlands: this is the Moist Mixed Grassland Ecoregion. A belt, representing a transition from the grasslands to the south and the boreal forest to the north, extends diagonally from southeast to northwest across the southern part of the province. Summers are cooler in this region, winters are longer and colder, and snow cover is more continuous than in the regions to the south and west. Summer evaporation and precipitation rates in this area are almost equal, which minimizes the potential severity of the late summer moisture deficits. Here, a mosaic of trembling aspen surrounds numerous wetlands, forming groves in a sea of plains rough fescue grasslands: this is the Aspen Parkland Ecoregion.

The smooth climatic and vegetation zonation that extends from southwest to northeast across the southern part of the province is interrupted by a prominent upland. High elevations result in a climate that is cooler and more moist than the surrounding dry grasslands. Vestiges of a montane forest, dominated by lodgepole pine, that once extended all the way to the Rocky Mountains remain to this day: this is the Cypress upland.

Many small wetland areas, or sloughs, occur throughout the Prairie Ecozone. In the more humid parts, these sloughs tend to be more permanent, the water is relatively fresh, and they are ringed by willows and trembling aspen. In drier parts of the ecozone, however, the sloughs are less permanent and more saline, and the transition from the wetland to the grassland is a sharp one. Most freshwater wetlands are characterized by emergent vegetation such as sedges, bulrushes, cattails, and reed grasses on their margins. In the open water, submerged growth of pondweeds, yellow watercrowfoot, and greater bladderwort may be present. Saline wetlands do not have a marginal ring of willows, but rather have shorelines heavily encrusted with white salts and usually bare of vegetation except for a few salt-tolerant plants like red samphire. Salt-tolerant grasses, such as seaside arrow-grass and alkali grass, grow at the margin of the salt crusts.

Wildlife. Historically, the prominent species on the prairie was the Bison. The Pronghorn antelope, though an animal of the open plains, ranged well into the parkland. Elk grazed on the grassland around the edges of aspen groves. The wolf was the main predator of the ungulates. Settlement and widespread cultivation of the grasslands has caused some species to come near the brink of extinction (as in the case of bison) or to currently occupy a small portion of their former range. An abundance of assorted mice and voles inhabit the matted vegetation in unburned or ungrazed grassland. The thirteen-lined ground squirrel also prefers longer grasses. Richardson’s ground squirrel forms extensive colonies on knolls, gravel ridges, and overgrazed areas. The northern pocket gopher spends most of its life underground, feeding on succulent roots in pastures and haylands; its mounds of soil become an annoyance during haying. Coyote, red fox, and the re-introduced swift fox feed chiefly on Rodents, Birds, and insects. The badger feeds predominantly on ground squirrels, which it captures by digging (see Carnivores). The snowshoe hare inhabits aspen groves during the day, emerging to feed at night, while the white-tailed jack rabbit frequents pastures, cultivated fields, and open, arid prairie, seldom penetrating wooded areas except as shelter from blizzards (see Hares and Rabbits). The striped skunk reaches its highest densities in agricultural areas, and the woodchuck has also prospered as a result of agricultural and Forestry practices.

Characteristic grassland birds include western meadowlark, Horned Lark, upland sandpiper, and chestnut-collared longspur. The vesper sparrow, clay-colored sparrow, chipping sparrow, and sharp-tailed grouse are more abundant on prairie adjacent to woodland. The brown-headed cowbird followed the bison herds and fed on insects associated with them; its migratory nature led it to lay eggs in other birds’ nests rather than build its own. The ferruginous hawk and Swainson’s hawk will nest on the ground in open arid prairie, while the red-tailed hawk is common to parts of the prairie that supply Trees for nesting. In the winter, large flocks of snow bunting and common redpoll frequent grasslands, fields, and road edges, feeding on seeds of forbs and grasses exposed above the snow.

The prairie has more fish species than the boreal plain, this being the result of additional warm water species being found in the Qu’Appelle, Assiniboine, and Souris River systems. Reptile species are most numerous in the prairie, preferring the warmth of a dry arid region. Fourteen species of Reptiles occur here, 11 of which occur in the mixed grassland. An additional three species of Amphibians occur in the prairie as compared to the boreal plain.

Human Activity. More than 80% of the economic activity of the province is generated in this ecozone, with agriculture as the dominant Land Use. Called the breadbasket of Canada, much of Canada’s and Saskatchewan’s cropland and rangeland and pasture are located in the Prairie Ecozone. The other major activities contributing to the economy are Mining (Coal, potash, mineral, and aggregates) and oil and gas production. Despite the dominance of agricultural activities on the landscape, the majority of the population is found in urban communities. The 1991 population of this ecozone was approximately 827,000 or 84% of the total population of Saskatchewan. Ten of Saskatchewan’s 13 cities are located in this zone, and 81% of the population lives in urban centres. Also, this ecozone has a higher proportion of its labour force in secondary industries than the national average, reflecting the importance of its major urban centres in serving national and international markets.

Agriculture has diversified considerably in recent years in the Prairie Ecozone, from traditional grain crops to more oilseed crops, such as Canola, Flax, and sunflowers. Producers have increasingly adopted more sustainable Farming practices, including Conservation tillage and reduced Summerfallow, reducing the risk of water and wind erosion. The Prairie Ecozone has also been experiencing a trend towards increased livestock production. Agriculture, and to a lesser degree urbanization, have transformed more than 80% of the native prairie landscape. Most of the rough fescue grassland has been ploughed, and much of the remainder has been significantly modified by livestock grazing and haying. Almost all of the tall-grass prairie is gone. Less than 20% of the once abundant mid-grass prairie remains in its native state, about one-quarter of the mixed-grass prairie and aspen parkland. Approximately 40% of the original 2 million hectares of wetlands have been converted to agricultural use. All landscape areas within this ecozone have been cultivated or grazed for at least 20% of their area, and many show 100% cultivation or grazing levels.

Over the past 100 years, the Prairie Ecozone has undergone development by natural resource industries, largely agriculture and forestry, but also oil and gas extraction and refining, hydroelectric power generation, fisheries, and mining. Although these industries have fostered a thriving economy and high standard of living, they have also greatly modified the original ecosystems, diminishing wildlife and plant populations. The Prairie Ecozone has vast amounts of a wide range of non-renewable resources, including oil, natural gas, potash, coal, Sodium Sulphate, and clay products; it currently contains 14,000 active oil wells and 7,000 active gas wells.

Forested lands are scattered, occurring in gullies, ravines, and areas of higher elevation. Generally the use of such forests has been for recreation or as a source of fuel wood. There is relatively limited commercial fishing activity in this zone. Commercial Aquaculture, gill netting and harvesting of brine shrimp, minnows, and leeches occur on selected prairie lakes. There are several private trout hatcheries. The Prairie Ecozone is a popular destination for anglers, providing almost half of all recreational fishing in the province. As well, 22% of the provincial trapping harvest occurs from this ecozone. Over half of the provincial total of hunting of big game and more than 80% of the hunting for bird species occurs in the Prairie Ecozone.

Just under 9% of this ecozone is in some form of park or protected area. Canada’s only national park dedicated to the protection of grasslands, Grasslands National Park, occurs in this zone. Saskatchewan’s Watchable Wildlife Society has identified 90 “eco-sites” in the province that represent areas with a high degree of natural significance for ecotourism. The Prairie Ecozone contains 55 of those sites.

Donald F. Acton, Glenn A. Padbury, Colette T. Stushnoff

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Further Reading

Acton, D.F., G.A. Padbury and C.T. Stushnoff. 1998. The Ecoregions of Saskatchewan. Regina: Canadian Plains Research Center and Saskatchewan Environment and Resource Management.