A reconstruction of the recent vegetational history of a prairie marsh, Eagle Lake, Iowa, from its seed bank

Abstract

Substrate samples were collected at four depths (0–5, 10–15, 20–25, and 30–35 cm) from six vegetation types at Eagle Lake, Iowa. The number of viable seeds in a sample was estimated by placing samples in environments appropriate for seed germination and counting the number of seedlings. Quantitative and qualitative differences in the composition of the seed bank at different depths and locations revealed that the marsh has two distinct vegetation areas. In the northern area, the vegetation changes cyclically. These cycles involve a rotation of three vegetation types: submerged, mudflat, and emergent ( Scirpus validus Vahl./ Typha glauca Godr.). In the southern (shallower) area, the composition of the seed bank indicated that there have been no cyclical changes in vegetation. The presence, however, of Typha seed in 0–5 cm samples and in some 10–15 cm samples (in numbers exceeding those normally found in contemporary Typha communities) in vegetation types presently dominated by Sparganium eurycarpum Engelm., Scirpus fluviatilis (Torr.) Gray, and Carex atherodes Spreng. suggest that, in recent years, Typha has declined significantly in the southern area. Because of the failure of their seeds to germinate under assay conditions or because the dominant species annually produces very little seed, most shallow-water emergent community types could not be detected in the seed bank.