Six years of submerged plant community dynamics in a freshwater tidal wetland

1. The dynamics of a submerged plant community were studied for 6 years in a freshwater tidal wetland. The degree and nature of change at several spatial scales (quadrat, transect and overall community) was determined, and the implications for community stability were assessed. 2. A high degree of change was recorded in 1 m(2) quadrats, and this was reflected in 10 m(2) transects as well. In quadrats, mean species richness changed every year. Species richness changed in >60% of quadrats each year. Stem number changed by as many as several 100 stems per quadrat from one year to the next. 3. Richness varied more among quadrats than among transects and varied less at the community level than among either quadrats or transects. Greater stability at the spatial scale of the whole community was reflected in high scores on the Jaccard and Morasita-Horn indices and Kendall's coefficient of concordance. 4. Although most of the submerged species were perennials, persistence at the local scale was low, and 4-year persistence exceeded 50% for only one species. Change in abundance was largely independent among the species. 5. In the face of great small-scale changes, species remain in the community (and the community persists) because of high recruitment rates.