It has been hypothesized that relatively large plant species/individuals self-thin to a lower density, and in doing so, leave patches of unused resources that may be captured by smaller species that require fewer resources. It has further been hypothesized that these unused resources will be distributed in a variety of 'patch' sizes such that a greater variety of species may colonize these 'physical space niches', enriching diversity and biomass production. We tested this theory by growing experimental monocultures of fifteen old-field perennial plant species. Monocultures were maintained through a single growing season, followed by two growing seasons within which colonization from the surrounding plant community was allowed to take place. Our results suggest that larger species had a greater diversity of colonists from the surrounding old-field communities, and increased biomass production, in support of our general predictions.  Contrary to predictions, post-thinning invasion had a significant negative impact on plot biomass.