Experimental evidence suggests that competition among plant species is generally hierarchical and that relatively large species are at a competitive advantage when competition is predominantly above-ground. However, regional species pools are dominated numerically by relatively small plant species, and small species generally have higher local densities of resident plants within natural communities. One explanation is that larger plant species suffer disproportionately more under effects of intra-specific competition (i.e. greater density dependence). We tested this prediction using ten herbaceous plant species in a competition experiment.