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Livestock producers in the Northern Great Plains value alfalfa (Medicago sativa L.) for increasing forage production and quality in grazing lands. However, alfalfa persistence can be poor, especially under grazing. Demand exists for alfalfa that can establish and persist in semiarid grazing lands. A naturalized population of predominantly yellow-flowered alfalfa (Medicago sativa L. subsp. falcata [L.] Arcang.) was found growing and reseeding on private and public rangeland in northwestern South Dakota. This naturalized alfalfa population demonstrates persistence in this semiarid environment. A study, initiated in May 2006 at the Antelope Range and Livestock Research Station near Buffalo, South Dakota, evaluated stand persistence and forage yield of 11 alfalfa populations transplanted into mixed-grass prairie. Populations were pure falcata, predominantly falcata, hay-type sativa, or pasture-type sativa populations. Transplants were space planted on 1-m centers within three exclosures (35 × 35 m) divided into two sections, which were either mob grazed by cattle or protected from mob grazing. Mob grazing began in August 2007 and continued periodically through 2008 and 2009. Survival, plant height, plant canopy diameters, and biomass data were collected. Grazing, dry spells, and ice sheets subjected alfalfa plants to substantial stress. High mortality of grazed plants occurred during the 2008-2009 winter. Hay-type sativa and pasture-type sativa populations exposed to mob grazing had poor final survival (<19%) and forage yield in July 2010. However, pure falcata and most predominantly falcata populations had higher survival (>38%) and forage yield. Low mortality and high yield of protected plants indicated that accumulated stress from mob grazing weakened grazed plants, increasing environment-related mortality (e.g., winterkilling). Falcata-based populations persistent under mob grazing and adapted to the regional environment have potential for use in the Northern Great Plains. © 2015 Society for Range Management. Published by Elsevier Inc. All rights reserved. The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information.