Wheat is a dry climate crop. Winter wheat is planted in milder climates, spring wheat in the north. Bulky item, best suited to water or rail transport. U.S. and Canada major exporters, China a major producer but for domestic consumption only.
Sheep can live in hillier and drier conditions than cattle.
Livestock ranching is extensive, i.e., requires a lot of land. Carrying capacity is the measure of what the land will support. So ranches tend to be large. Dry grassland is good for ranching, but unsuited for farming. Spread of irrigation is reducing ranching in U.S. because farming offers higher productivity per acre.