Grasslands represent one of the largest vegetation types on Earth and their existence is determined by water scarcity that in turn depends on precipitation and temperature. This vegetation type harbors a high diversity of plant species that mostly occurs at fine spatial scales because grasslands tend to be structurally simpler at coarser scales. Grassland species richness has strong and positive effects on primary production as a result of increasing niche complementarity with increasing diversity. Grasslands are among the most vulnerable ecosystems in the world because their diversity is threatened by human activity, mostly as a consequence of conversion into croplands.