1. The extent to which individuals experience inter- and intraspecific interactions through their spatial arrangements within diverse plant communities, whether because of confounding effects of species richness, evenness, or direct changes in species patch sizes on their neighborhood relationships, could affect grassland biomass production and its stability at community scales. Elucidating the ways in which neighborhood effects and species richness contribute to such community responses has important implications for how practitioners establish grasslands to meet forage production and conservation goals.

2. We assessed the effects of altering plant species richness (3 levels: 2, 4, or 8 forage species per plot) and seed arrangements (4 levels: species mixed and seeded or seeded in 0.0625 m², 0.25 m², or 1.0 m² single-species patches while maintaining plot-scale species evenness) on aboveground biomass production and its temporal stability in developing grasslands seeded with a suite of globally common forage species (three legumes, three cool-season grasses, two warm-season grasses).

3. Communities seeded with more species and those with their seeds arranged into smaller conspecific patches produced more biomass and were more temporally stable than those seeded with fewer species and larger conspecific patches. The effect of manipulating species arrangements is attributable to greater neighborhood scale interspecific interactions and stronger complementary effects. Furthermore, seeding species into conspecific patches resulted in communities that were 34% more productive, that were just as temporally stable, and that had similar diversity effects as those seeded with a species mixture, as is common in grassland reconstruction efforts.

4. Synthesis: In comparison with conventional mixed-seeding methods, seeding grasslands with high species richness and small, single-species patches may promote grassland reconstruction through increased biomass production, temporal stability, and complementarity effects. Our study highlights the importance of regulating intraspecific interactions within diverse communities for improving grassland biomass production and suggests that efforts to reevaluate methods used to establish forage and conservation grasslands could result in greater biomass production and stability in these systems.