These lands are characterized by grass, whether tall, short, or mixed. The taller grass occurs where there’s more rain, resulting in abundant grain crops. The short grass can be less than a few inches tall. In tropical grasslands, sometimes all of the year’s rain occurs within just weeks.
In North America, when the Rocky Mountains rose, they caused a rain shadow that killed the forests for hundreds of miles east of them in the Midwest, resulting in the prairies of the Midwest. For tens of thousands of years, Native Americans periodically burned these grasslands, preventing trees from growing there. This was done to extend the land for their livestock to graze.
Trees will steadily encroach on prairies without the interference of humans or grazing animals, so keep this in mind when placing them. They will exist due to rain shadows. Our species may cause them to remain intact; otherwise, the land will first turn into a savannah and then a forest. We’ll want some nomadic peoples to dwell there, with herds of grazing animals, like the American Indians.