Buffalograss is a warm-season perennial shortgrass. Parts of the shortgrass prairie are untouched and pastoral. There are two significant population trends currently impacting the shortgrass prairie region. Blue grama is the dominant species of the US shortgrass steppe ecoregion. The ecoregion is encompassed by the tallgrass and shortgrass prairies. The Mixed Grass prairie was recognized as a mixture of the tallgrass and shortgrass prairies. Savanna surrounded much of the continent's central tallgrass prairie and shortgrass prairie. A mixed-grass prairie is an ecotone located between the tallgrass prairies and shortgrass prairies. The area surrounding Brooks is dry mixed grass/shortgrass prairie. The Black Mesa plateau there is part of the Rocky Mountains and the shortgrass prairie. Oklahoma's grasslands are made up of shortgrass, mixed-grass and tallgrass prairie. They occur more often in mixed-prairie associations than in shortgrass associations. On shortgrass pasture, bison predominately consume warm-season grasses. Steppes/shortgrass prairies are short grasslands that occur in semi-arid climates. The shortgrass prairie has a long human history.