Vegetation of a particularly diverse area of undrained flood-plain mire is described. Factors and processes important in determining the distribution of community-types within the study area have been investigated. Investigation of the alluvial stratigraphy has revealed the presence of a complex pattern of peat cuttings. Succession within the peat cuttings, with appropriate vegetation management, has led to the formation of Cladium mariscus-, Phragmites communis- and Juncus subnodulosus-dominated fen vegetation and, in some areas, poor-fen communities with much Sphagnum. In areas not cut for peat, management his also sustained various rich-fen herbaceous communities(different to those of the cuttings); in its absence, fen carr develops. The differences in successional development in peat cutting areas and those not cut for peat is mainly due to difference in hydrological status. Long term experiments established to examine effects of different management techniques are described. Studies of peat and peat water chemistry in a representative selection of community-types has demonstrated local areas of high salinity, caused by incursions of brackish water due to exceptionally high tides and, particularly, the influence of underlying estuarine deposits. Although large areas are flooded by river water there is little evidence for eutrophication, except very locally. Indeed, 'seral oligotrophication' is occurring in isolated areas. This may preceed, but is not a pre-requisite for, Sphagnum invasion. The most species-rich communities are developed in non-saline areas with a fairly stable water level; they may, however, be dependent upon flooding by river water for maintenance of their base status.