much of the nama karoo biome is used for sheep and goat farming, providing mutton, wool, and pelts for local and international markets, especially since livestock can frequently be provided with a regular supply of water from boreholes. overgrazing exacerbates the erosion caused by the violent thunderstorms that occur, infrequently, in the summer. it also promotes the replacement of the grasses by shrubs, especially the less edible varieties such as the threethorn ("rhigozum trichotomum"), bitterbos ("chrysocoma ciliate"), and sweet thorn ("acacia karroo"). however, there are few rare or red data book plant species in the nama karoo biome.