摘要：

SummaryAmbrosia trifida L. is an annual plant found in repeatedly disturbed ground in the midwestern and eastern United States. When present, it dominates the community, producing most of the plant biomass and suppressing all associated species. When A. trifida was selectively removed in field plots early in the growing season, the biomass of the remaining species, their density and species diversity increased but the biomass of the community decreased. With A. trifida the total standing above-ground plant biomass of the other species was 43.7 gm_-2, their density was 86 plants m⁻² and the species diversity was 0.21. Without A. trifida the corresponding values were 666 g m ⁻², 584 plants m⁻², and 1.64. Total above-ground biomass of the community was 1640 with and 666g m⁻² without A. trifida. Ambrosia trifida produced 97 % of the plant biomass. The negative correlation between biomass and diversity was undoubt

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