A model is constructed in which seed production by individual annual plants within a population is a function of the number and species of individuals within each of several concentric neighborhoods. The effect of increasing competition is to reduce seed production in a hyperbolic fashion, and the contribution of each individual to this effect is in inverse proportion to the square of its distance from the test individual. A simple monospecific version of this model was tested on populations of 2 annual knotweeds. A least-squares fit accounted for >80% of variation in seed production. This model provides an alternative to density in describing plant populations. A monospecific aggregated version can be seen as an extension of the inverse-yield law.-from Author