||Native warm-season perennials (NWSP) are infrequently used as forage species in grasslands managed for livestock even though they possess a variety of positive attributes such as high productivity and low input requirements. Increasing NWSP diversity in sown mixtures may have other benefits such as increased forage yields, improved forage nutritive value, and reduced weed invasion. Some research suggests that these positive diversity effects are due to plant interactions, while other results indicate that effects are due to the presence of just a few species. We hypothesized that managing NWSP mixtures for high diversity may enhance these benefits. In 2008, we established an experiment using 3 native plant mixtures containing 1, 4, or 10 species to evaluate how sown forage diversity affected forage yield and species composition. In both 2008 and 2009, sown forage yields were lowest in monocultures (52.4 kg/ha in 2008 and 485.6 kg/ha in 2009) and greatest in 4-species (390.7 kg/ha in 2008 and 1919.9 kg/ha in 2009) and 10-species mixtures (813.6 kg/ha in 2008 and 1726.6 kg/ha in 2009), but weed biomass was not affected by sown mixture in either year. Forage nutritive values were generally acceptable for maintaining beef cows in all 3 treatments (averages for NDF: 41‐67%, ADF: 25-38%, CP: 10-17%), although quality tended to decrease as native grass cover increased. We also established a small plot experiment sown with randomly-assembled mixtures containing 1, 2, 4, 6, or 10 species to determine mechanisms that explain the diversity-productivity relationship; i.e., true diversity effects or sampling effects. We found multi-species plots overyielded, an effect that shifted over time. Our results suggest that NWSPs can be a viable forage option and that managing for diverse mixtures may improve productivity.