Submitted to: American Society of Agronomy Monograph Series
Publication Type: Other
Publication Acceptance Date: 8/27/2003
Publication Date: 9/22/2004
Citation: Burns, J.C., Mcivor, J.G., Villalobos, L.M., Vera, R.R., Bransby, D.I. 2004. Grazing system for c4 grasslands: a global perspective.. American Society of Agronomy Monograph Series. Interpretive Summary: Warm-season grasses compose the major grasslands of the world, which are found in Africa, South and Central America, Australia and North America. This chapter addresses these grasslands in terms of climates, soil types and warm-season grass species that are found in the various climates of these continents. Further management strategies in terms of fertilization and defoliation are described for the grazing systems that have evolved. Finally, the type of animal production systems and their role in the associated sociology of the regions are considered.
Technical Abstract: Grasslands are typically found in the interior of the continents ranging northward to about 55o in North America and Asia and south to about 40o in South America. In the temperate zones, treeless prairies, steppes, and pampas dominate and in the tropical and subtropical zones, savannas are found with varying proportions of shrubs and trees. Grasses generally dominate over shrubs in temperate zones where extended rains occur in the summer, and C4 grasses dominate in tropical zones where dry winters give way to wet summers. The two major factors that determine vegetation types are temperature and rainfall. The biomes (climate, soil, and vegetation) that have evolved are the tundra (-57 to 16oC; 100 to 150 mm rain), coniferous forest (-54 to 21oC; 350 to 2000 mm rain), deciduous forest (-30 to 38oC; 600 to 2250 mm rain), temperate grassland (-30 to 45oC; 300 to 2000 mm rain), savannas or warm-climate grasslands (13 to 40oC; 250 to 900 mm rain), and tropical rain forest (18 to 35oC; 1250 to 12 500 mm rain). The C4 grasses occur mainly in the deciduous forest, temperate grassland, and savanna biomes. The characteristics of the grazing system that evolves in most grasslands, but especially in the tropics, is determined to a larger extent by rainfall distribution patterns as opposed to annual totals . Grasslands (range and pasture) cover about 51% of the total land area of the world and are found mainly in Africa, Australia, South America, and North America. Within these continents, grasslands compose about 90% of the agricultural land in Oceania (Australia), 82% in sub-Saharan Africa, 81% in South America (70% in Central America), and 53% in North America . The largest decline in world grasslands over the past century has occurred in North America, averaging 79%, with most of the decline occurring in the tallgrass prairie. The focus of this chapter-grazing systems that have emerged to utilize C4 grasses in the major grasslands of the world-restricts discussions to these four continents.