Mixed Grassland (#156)

MIXED GRASSLAND (#156) The Mixed Grassland ecoregion is the southernmost and driest of Canada’s prairie ecoregions. A northern extension of the shortgrass prairies that stretches south to Mexico, this ecoregion is characterized by the vast open grasslands of the Great Plains, with prairie potholes and several large shallow lakes. It provides habitat for over 35 species at risk and is an important region for waterfowl nesting. The semi-arid climate limits crop production. Approximately 42% of this ecoregion remains in natural cover and almost 11% is within conserved/ protected areas, including 4% in community pastures. LOCATION Arching from southcentral Saskatchewan to southcentral Alberta along the U.S. border, this ecoregion forms the northern part of the semi-arid shortgrass prairie in the Great Plains of North America. This ecoregion extends southward along the Missouri River into northeastern Montana, northwest and central North Dakota, and central South Dakota (in the U.S., this ecoregion is called the Northwestern Mixed Grasslands). CLIMATE/GEOLOGY The Mixed Grassland ecoregion generally has long, dry and cold winters, with a short, warm and a relatively wet spring and summer. The mean annual temperature is approximately 3.5⁰C. Mean summer temperature is 16⁰C and mean winter temperature is approximately -10⁰C. The mean annual precipitation ranges from 240 to 350 millimetres, with higher rain and snowfall in the eastern portion. Overall, this ecoregion is semi-arid, and compared to other regions of the Prairies, it has relatively low amounts of snow cover. Western sections of the ecoregion experience a higher frequency of warming Chinook winds in the winter. The Mixed Grassland is a gently rolling landscape with flat expanses in some areas. There is a wide diversity of other landscapes, including scattered alkaline lakes, salt flats, inland dunes and badlands. Prairie potholes are less common than in the Moist Mixed Grassland and Aspen Parkland ecoregions, with the exception of the Missouri Coteau. VEGETATION The Mixed Grassland is characterized by short and mid-sized grasses and sedges intermixed with prairie wildflowers and low shrubs. The native grasslands are dominated by needle-and-thread (Hesperostipa comata), western wheatgrass (Pascopyrum smithii) and prairie junegrass (Koeleria macrantha), with blue grama (Bouteloua gracilis) and blunt sedge (Carex obtusata) in the driest areas or under heavy grazing. A variety of shrubs and herbs also occur, including hoary sagebrush (Artemisia cana), prickly rose (wild rose) (Rosa acicularis) and brittle prickly-pear (Opuntia fragilis). Trees are rare. Thickets of scrubby trembling aspen (Populus tremuloides), eastern cottonwood (Pop- ulus deltoides), American silverberry (wolf-willow) (Elaeagnus commutata), snowberry (Symphoricarpos albus), Saskatoon serviceberry (Saskatoon berry) (Amelanchier alnifolia) and choke cherry (Prunus virginiana) are found in low areas, river slopes and coulees. Fire, grazing by bison and drought were once key natural disturbances to this grassland ecosystem and played important roles in the abundance and 1 Ranking categories for biodiversity threat and conserved/protected area are relative to other ecoregions in the southern Canada study area (5=highest, 4=higher, 3=high, 2=low, 1=lower, 0=lowest). The lowest score for conserved/protected area is 1. For biodiversity and threat, the highest category based on measures and criteria approach is used. Photo by Calvin Fehr Kyle Marquardt MIXED GRASSLAND (#156) FRESH WATER AND COASTS The ecoregion is dominated by the Nelson River drainage (Hudson Bay basin). Major rivers include Upper and Lower South Saskatchewan, Qu’Appelle and Red Deer. The southern portion of the ecoregion includes the headwaters of the Missouri River, which is in the Mississippi River drainage (Gulf of Mexico basin) (Figure 1). Some parts of the Mixed Grassland ecoregion are dotted with concentrations of semi- permanent and seasonal wetlands, often referred to as prairie potholes or sloughs. There are also several permanent and seasonal lakes that are generally shallow and alkaline, such as Old Wives Lake south of Moose Jaw. Other major lakes include Pakowki Lake and Many Island Lake. Lake Diefenbaker was created by damming the South Saskatchewan River and Qu’Appelle River (completed in 1967), and Lake Newell is a reservoir on the Bow River (constructed in 1914). Wetlands and water cover approximately 4.3% of the ecoregion, although this is likely an under-estimate as smaller potholes would not be included in this figure. Mike Dembeck AT-RISK VEGETATION COMMUNITIES Rare vegetation communities have not been well-documented from this ecoregion. Asso- ciations that are of potential global conservation concern include: • longleaf wormwood - prairie sandreed (Artemisia longifolia - Calamovilfa longifolia) sparse vegetation WILDLIFE Photo by Karol Dabbs The mosaic of grasslands and wetlands provides habitat for a diversity of species, including a large number of species that are not found in other ecoregions. The Mixed Grassland ecoregion has a very high richness of mammals and breeding birds compared to other ecoregions in southern Canada. Common wildlife species include pronghorn (Antilocapra americana), mule deer (Odocoileus hemionus), white-tailed deer (Odocoileus virgin- ianus), coyote (Canis latrans), Richardson’s ground squirrel (Urocitellus richardsonii), western meadowlark (Sturnella neglecta) and yellow-headed blackbird (Xanthocephalus xanthocephalus). AT-RISK PLANTS AND ANIMALS There are over 35 national species at risk in the Mixed Grassland ecoregion. Sites with higher numbers of national species at risk include the intact prairies in and around Grasslands National Park. In addition, there are approximately 20 species of global conservation concern, with the highest number associated with the Great Sandhills region of Saskatchewan (Figure 2). Species at risk include: • black-tailed prairie dog (Cynomys ludovicianus) • slender mouse-ear-cress (Virgate Halimolobos) (Halimolobos virgate, plant)* • Ord’s kangaroo rat (Dipodomys ordii) • gold-edged gem moth (Schinia avemensis)* • sage thrasher (Oreoscoptes montanus) • swift fox (Vulpes velox)* • greater short-horned lizard (Phrynosoma hernandesi) *nationally and globally at risk (NatureServe) Photo by Branimir Gjetvaj MIXED GRASSLAND (#156) LAND USE Agriculture dominates this prairie landscape (Figure 3). Lands are cultivated on the plains, and there is extensive irrigation in the western portion of the ecoregion. Many of the native prairie grasslands are used for ranching. Oil and gas extraction is common in the western portion of this ecoregion. The rate of land conversion (2000-2010) in this ecoregion is one of the highest in southern Canada. This is primarily native managed grasslands being converted to cropland (Table 1). The area of these grasslands decreased by 30%, while the area of crop increased by about the same percentage. More recent data shows that more than 236,000 hectares (more than 583,000 acres) of previously plowed land was returned to perennial cover. It is not known if this is a trend in land cover, or if it represents crop rotation practices. Major communities include Medicine Hat, Leader, Swift Current, Assiniboia, Maple Creek, Shaunavon and Kindersley. The total population Photo by NCC (2016) is 204,767, with a growth rate of 7.8% since 1996. CONSERVATION CONCERNS The most significant threat to this ecoregion is habitat loss, including the on-going conversion of wetlands and native grasslands. Compared to the rest of southern Canada, this ecoregion has experienced a high recent rate of conversion of natural habitats to agriculture, and it ranks higher for the threat of lack of water (based on water demand verses water supply). High-ranking threats identified from the Nature Conservancy of Canada’s (NCC’s) Natural Area Conservation Plans (NACPs) in this ecoregion include invasive terrestrial species and droughts resulting from climate change. These threats may not be relevant to all areas of the ecoregion. Populations of grassland birds and shorebirds that breed in this ecoregion have been rapidly declining. CURRENT CONSERVATION STATUS With 42% natural cover, the Mixed Grassland ecoregion has some of the largest blocks of intact prairie habitat remaining in Canada. The largest intact blocks of habitat occur along the U.S. border, in the Great Sandhills region, and the area north of Medicine Hat in and around the Canadian Forces Base Suffield National Wildlife Area. This ecoregion is fragmented; however, there are several major corridors along the river valleys. A major north-south corridor extends from the U.S. border around and through the Cypress Uplands ecoregion into the intact grasslands of east-central Alberta (Figure 4). Approximately 11% of the ecoregion is conserved (Figure 5). This includes a large area (3.9%) of federal and provincial pasturelands. The amount of conserved area ranks second in the Prairies ecozone (after Cypress Uplands). This ecoregion also has a higher percentage of landform features conserved than most other ecoregions in the Prairies ecozone. Key Biodiversity Areas (KBAs) in this ecoregion focus on important areas for migratory and breeding waterfowl and shorebirds. KBAs include Bigstick Lake Plain, Chaplin Lake, Chappice Lake, East Lake Diefenbaker, Luck Lake, Old Wives Lake, Pakowki Lake, Reed Lake, South Saskatchewan River and Willowbunch Lake. NCC has three active NACPs that cover 31.6% of the ecoregion:

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