Effects of Hydrological Regimes on Competitive Interactions of Schoenoplectus Fluviatilis and Two Co-Occurring Wetland Plants

We investigated the effects of different hydrological regimes (wet [flooded at a constant water depth for duration of the study], cycle [reflooded at eight weeks following natural drying], and wet–dry [initially flooded and allowed to naturally dry for duration of the study]) on the competitive ability of  Schoenoplectus fluviatilis  (Torr.) M. T. Strong with an annual, native wetland plant ( Polygonum pensylvanicum  L.) and a perennial, wetland plant ( Schoenoplectus tabernaemontani  [C. C. Gmel.] Palla). To assess competitive response of the plants, we used a greenhouse target-neighbor study with neighbor plants planted at varying densities (0 [control], 1, 10, and 15 plants pot −1 ). Our results suggest that  S. fluviatilis  is competitively superior to  S. tabernaemontani  and  P. pensylvanicum .  S. tabernaemontani  and  P. pensylvanicum  biomass declined by 90% and 75% in presence of  S. fluviatilis , respectively. However, the competitive ability of  S. fluviatilis  was generally not enhanced by flooding regime. The competitive coefficients of  S. fluviatilis  were similar among the three hydrological regimes under intraspecific competition and interspecific competition with  S. tabernaemontani , but for interspecific competition with  P. pensylvanicum , the competitive coefficient for  S. fluviatilis  was higher for the cycle treatment compared to the wet–dry and dry treatments. Interestingly,  S. tabernaemontani  was a strong competitor against  S. fluviatilis  in the wet and cycle treatments, indicating that maintaining longer hydroperiods could be used as a management tool to encourage growth of  S. tabernaemontani  and reduce encroachment of  S. fluviatilis .