Biodiversity and plant productivity in a model assemblage of plant species

We examined productivity as a function of biotic diversity. We manipulated plant species richness as an experimental factor to determine if productivity (net above ground primary productivity or NPP) is affected by changes in plant diversity (species richness). We constructed 164 assemblages that varied in species richness and measured their biomass at the end of one growing season. The plants were drawn from a pool of 16 species of self-pollinating annual herbs common to English weedy fields. On average, species-poor assemblages were less productive. Results also showed, however, that species-poor assemblages had wider ranges of possible productivities than more diverse assemblages.