Figure 3. Total weed biomass means by entries and exponential trends for plots including the most weed suppressive species (closed symbols) and excluding such species (open symbols) as a function of seeded species richness in two Iowa locations under two harvest managements averaged over 2 yr: (A) Boone–one harvest; (B) Boone–three harvests; (C) Ames–one harvest; and (D) Ames–three harvests. P values for the linear contrasts on log-transformed weed biomass are shown. Equations for significant regressions (P < 0.05) are shown. The two slopes in each graph for environments B, C, and D, are not different at P = 0.05.