In New England, saltmeadow cordgrass, saltgrass, saltmeadow rush, and dwarf smooth cordgrass dominate the upper marsh. There is a distinct boundary between low marsh and high marsh at the elevation of mean high tide. The upper boundary of the high marsh is determined by the elevation of exceptional high tide. Where water is slowed and sediments drop out, sand- and mudflats are created. This creates barrier profiles that are low and flat.
Ocean tides are the dominant hydrologic feature of northern cordgrass prairie.
Estuarine wetlands are influenced by both tides and inland hydrology. In Connecticut, tall smooth cordgrass is a fairly accurate indicator of the landward extent of mean high tide. Dwarf smooth cordgrass forms extensive stands just above the low marsh. Above the dwarf smooth cordgrass zone, common reed, saltmeadow cordgrass, and saltgrass predominate. Common reed forms pure or mixed stands, saltmeadow cordgrass forms nearly pure stands, and saltgrass is commonly intermixed with other species.