Factors Affecting Recruitment from the Seed Bank of Sedge (Cladius mariscus) Dominated Communities at Wicken Fen, Cambridgeshire, England

Abstract

This paper attempts to identify factors which account for variation in the species composition of standing vegetation in four Cladium mariscus dominated areas of Wicken Fen, a wetland nature reserve. It was assumed that either the species composition of the seed banks, or the factors affecting recruit- ment from the seed banks, would vary. This distinction would help explain the ecology of fen succession and help in conservation management. Neither the species composition of the seed banks nor nutrient availability in the peat showed significant differences. However, differences were found in the probability of flooding, light intensity at ground level, and in peat surface mois- ture and temperature regimes. The nature of the standing vegetation appeared related to two factors: (1) the presence/absence, and timing of the management practice of mowing and harvesting, and (2) the probability, frequency and dura- tion of winter and spring floods as suggested by Godwin & Tansley (1929) model. An elaboration of that model suggests that the dense canopy created by a pure stand of the non-deciduous perennial Cladium mariscus creates a micro- environment inimical to germination of other species. As the habitat dries, or following the mechanical removal of the canopy by harvest, the ability of the Cladium mariscus to maintain the dark, damp, cool ground-level micro-climate is reduced, the rate of recruitment from the seed bank is increased, and the species richness of the standing vegetation is increased. This suggests that if the habitat is to be preserved the present mowing regime for carr control should be re- evaluated.