There is increasing recognition that both competition and facilitation are important drivers of plant community dynamics in arid and semi-arid environments. Decades of research have provided a litany of examples of the potential for shrubs as nurse plants for establishment of desirable species, especially in water-limited environments. However, interactions with the existing understory community may alter the outcome of interactions between shrubs and understory plants. A manipulative experiment was conducted to disentangle interactions between a native forb species (Penstemon palmeri A. Gray), a native shrub (Artemisia tridentata Nutt.), and a diverse understory of exotic and native forbs and grasses in a semi-arid shrubland of Northern Utah, USA...