Effect of native Suaeda japonica structure on the initial seed settlement of an invasive plant Spartina anglica

The relationships between native halophytes and initial seed settlement of Spartina anglica in the field are not well-studied. We therefore investigated the effect of the native halophyte Suaeda japonica on initial settlement of the invasive Spartina anglica on a tidal flat. The seed bank among native vegetation was compared with an unvegetated mudflat, and the effects of inundation on seed germination were tested. Five flooding duration treatments were compared: moistened, permanently-inundated, and inundated for 1, 2, or 3 h per day. Seed bank density was significantly higher where native vegetation (7.1 +/- 1.3 seeds m(-2)) than on the unvegetated mudflat (0.6 +/- 0.3 seeds m(-2)). Seed germination tests showed no significant differences among inundation treatments (log-rank test, p > 0.05). The broad range of conditions in which seeds can germinate allow Spartina anglica to become established widely in mudflat environments. Results suggest that native halophytes may function as an effective seed trap promoting initial settlement and establishment of the invasive Spartina anglica.