Production characteristics of the mixed prairie: constraints and potential.
The mixed prairie represents the most arid region of the Northern Great Plains in Canada. Approximately 6.5 million ha of the original total of 24 million ha have retained their native character. The native prairie supports about 5.3 million animal-unit-months or about 15% of all beef cattle present on the Canadian prairies. A large portion of the area is dominated by either needle-and-thread (Stipa comata) or western wheatgrass (Agropyron smithii [Elymus smithii]), both cool season grasses, and associated with blue grama (Bouteloua gracilis) a warm season grass. These species define the major plant communities of the mixed prairie and determine their production potential. However, their production is limited by available water during the growing season and by soil nutrients; factors which also influence botanical composition. Grazing imposes a significant impact on the grasslands by altering the water and nutrient cycles, through defoliation and reduced plant litter, and eventually by affecting the botanical composition. Removing litter may reduce forage production by up to 60% and repeated utilization will favour the more drought tolerant but less productive species. Forage production may be increased by sowing introduced species, which have a greater shoot:root ratio than native grasses, or with fertilizer application. Livestock production may be increased by the use of grazing systems.