Grazing lands (rangelands) occupy 26% of the earth's land surface, more than twice the area of cropland. Much of this land is too dry for raising crops. Animals grazing on these lands convert plant material that would otherwise be unusable by humans into meat, which humans can use. In addition to their role in livestock production, rangelands are important reservoirs of biodiversity. In the United States, more threatened species exist in rangelands than in any other biome.