Introducing exotic forages in the attempt to enhance livestock and wildlife forage has been practiced widely for over a century. These forage species are selected for traits conferring persistence under stress, potentially yielding invaders that transform native plant communities. Using standardized systematic review guidelines and meta-analytical techniques we quantified effects of exotic forage invasion on change of native plant community structure, and compared the magnitude and direction of change across exotic forage species, plant functional groups, and structure of plant communities. Our study of 13 exotic forage species in North America (six C₄ grasses, three C₃ grasses, and four legumes) yielded 35 papers with quantitative data from 64 case studies. Nine of the 13 species met our inclusion criteria for meta-analysis. The overall effect of exotic forage invasion on native plant communities was negative ( =  −0.74; 95% confidence interval [CI]: −0.29 to −0.25). The effect size was most negative for two C₄ grasses, Lehmann lovegrass and Old World bluestems. A negative effect was also expressed by C₃ and C₄ grass functional groups, and these effects were stronger than for legumes. Effect size differed among measures of plant community structure, with the greatest negative effect on native plant biomass and the least negative effect on species evenness. Weighted fail-safe numbers indicated publication bias was not an issue. Exotic forage species are important for agricultural production but may threaten complex multi-functioning landscapes and should be considered as a subset of potentially invasive exotic species. Characteristics making exotic forages different from other exotic plants hinge on pathways of selection and dispersion: selection is based on persistence mechanisms similar to characteristics of invasive plants; dispersion by humans is intentional across expansive geographic regions. Exotic forages present a complex socio-ecological problem exacerbated by disconnected scientific disciplines, competing interests between policy and science, and organized efforts to increase food production.

Nomenclature: Lehmann lovegrass, Eragrostis lehmanniana (Nees); Old World bluestems, (plains) Bothriochloa ischaemum var. ischaemum (L.) Keng. and (yellow) Bothriochloa ischaemum var. songarica (Rupr. ex Fisch. & C.A. Mey.) Celarier & Harlan.

Management Implications: The breeding, selection, and introduction of exotic forages have led to changes in native terrestrial plant communities in North America. Although not all exotic forages have become invasive, many have become problematic and shown aggressive expansion into areas beyond the initial plantings. Potential changes to the native plant community include reduced species richness, evenness, and diversity, and lower total cover and biomass. These exotic forage species are successful invaders because they are selected for traits conferring persistence under stress such as grazing, repeated haying, and environmental stress. Many of the desirable traits selected for in forage species are similar to traits common in invasive plants such as ease of establishment, high seed production with extensive longevity, vigorous vegetative reproduction, rapid growth rate, competitive resource use, and resistance to removal and predators (insects and disease). Managers should carefully consider invasion potential to guide species selection when exotic forage is proposed in a hay or permanent pasture scenario. Managers may also consider using native seed mixes, especially for restoration of natural areas, but native seed costs are currently prohibitive and exotic seed is typically cheaper. This cost discrepancy continues to constrain reseeding natural areas or planting of Conservation Reserve Program fields with seed mixes to optimize wildlife use. We also suggest that managers monitor areas of exotic forage presence and begin measuring expansion over time into other areas. Our results also suggest that managers consider limiting the establishment of wildlife food plots with exotic forage species that may invade beyond the planted areas. Finally, dialogue between managers and other stakeholders is needed to discuss innovative solutions for exotic forage invasion situations or potential situations.