Excluding root competition in the grass community provided favourable conditions for R. robusta seedlings to establish, suggesting that root competition from the grass is more important in maintaining separate grass communities, and that any differences in soil properties are less important in influencing such processes. Our study presents an example where a species' fundamental niche may be differerent from its realized niche, as a result of competitive interactions. Keywords: Competitive exclusion, Grass–shrub ecotone, Root competition, Seedling establishment, Spatial segregation of communities, Succulent Karoo; Succulent shrubs.