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The effect of canopy removal, a form of non-lethal disturbance, was assessed for the interaction between two co-occurring American East Coast salt marsh angiosperms, Schoenoplectus americanus (Pers.) Volkart ex Schinz and R. Keller and Distichlis spicata (L.) Greene, in a greenhouse replacement series experiment. In mixture, aboveground production of S. americanus was significantly higher than production of D. spicata. When plant canopy was experimentally removed, this difference was stronger (366±35gm⁻² vs. 139±41gm⁻²; P=0.0033) than when it was left intact (383±44gm⁻² vs. 215±67gm⁻²; P=0.07). Belowground yield of S. americanus was significantly higher than yield of D. spicata (113±27gm⁻² vs. 57±20gm⁻²; P=0.047) in pots with canopy removal. In control pots, there was no significant difference between the belowground yields of the two species (P=0.23). Comparisons of relative yields of the two species (based on biomass and stem density measurements) indicated that S. americanus suppressed D. spicata when the plant canopy was removed. This suggests that canopy disturbance gives S. americanus a competitive advantage over D. spicata in mixed compositions. Anthropogenic disturbances such as prescribed fire and grazing used as land management techniques are likely to influence competitive interactions and play a key role in plant community productivity.
