The marsh vegetation of three Connecticut River oxbows: a ten-year comparison.

The floras and vegetation of marshes in three large Connecticut River oxbows of differing ages in western Massachusetts were studied and compared in 1974 and again in 1984. Marshes at Hatfield in the most recently formed of the three oxbows occur in zones that parallel much of the old river bank. Marshes in Ned's Ditch, Northampton, an oxbow segment that was cut off from the river around 710 yr. B.P., occur within nine scattered ponds surrounded by swamp forest. Marshes at Whately in the oldest oxbow are confined to the vicinity of a single pond. In all three oxbows, a high marsh is dominated by Onoclea sensibilis and a low marsh by Lemna minor and Nuphar variegatum. Zones of emergent mid marsh vegetation are distinctive at each oxbow. Marshes at the two younger, regularly flooded oxbows share numerous species with the herb strata of adjacent swamp forests and remained relatively unchanged throughout the study period except for an increase in woody seedlings at the Hatfield high marsh. The Whately marshes share few species with adjacent forest; species richness in high and emer gent zones of the Whately marshes declined sharply over the decade.