Espinal is a term that refers to the spiny nature of the vegetation contained within it and is located in central Argentina. The espinal has a varying tree structure that is predominantly comprised of the genus Prosopis and ranges from tall to short open and closed woodland and savanna systems. Soils are the main reason for changes in tree structure. Understory species include thorn shrubs that vary in density based on historic use (cattle versus sheep grazing) and fire patterns, and grass species that fall within three categories: winter palatable, winter unpalatable and summer palatable. Grazing pressure has lead to a dominance of winter unpalatable species in large areas.