Here's why:
* Vast, flat, and treeless: The Great Plains are characterized by their vast expanse of flat, open land with very few trees.
* Dominated by grasses: The dominant vegetation is grasses, ranging from short grasses in the west to tallgrass prairies in the east.
* Semiarid to humid climate: The Great Plains receive moderate rainfall, generally decreasing from east to west. This supports a variety of grasses, but not enough for dense forests.
While other terms like prairie, steppe, and savanna can be used to describe parts of the Great Plains, grassland encompasses the entire region and its defining characteristic.
