PRODUCTION CHARACTERISTICS OF THE MIXED PRAIRIE - CONSTRAINTS AND POTENTIAL

The mixed prairie represents the most arid region of the Northern Grea t Plains in Canada. Approximately 6.5 M ha of the original total of 24 M ha have retained their native character. The native prairie support s about 5.3 M animal-unit-months or about 15% of all beef cattle prese nt on the Canadian prairies. A large portion of the area is dominated by either needle-and-thread (Stipa comata Trin. + Rupr.) or western wh eatgrass (Agropyron smithii Rydb.), both cool season grasses, and asso ciated with blue grama [Bouteloua gracilis (H.B.K.) Lag. ex Steud.] 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 seas on and by soil nutrients; factors which also influence their species c omposition. Grazing imposes a significant impact on the grasslands by altering the water and nutrient cycles, through defoliation and reduce d plant litter, and eventually by affecting the species composition. R emoving litter may reduce forage production by up to 60% and repeated defoliation will favour the more drought tolerant but less productive species. Forage production may be increased by seeding introduced spec ies, which have a greater shoot to root ratio than native grasses, or with fertilizer application. Livestock production may be increased wit h the use of grazing systems. However, the benefits of each practice o n the mixed prairie must be assessed in terms of their cost, their imp act on the environment, and the reduced or lost value for other users.