Plant Communities of Rich-Fen Systems in England and Wales: I. Introduction. Tall Sedge and Reed Communities

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Abstract
Floristic data were collected from 298 predominantly lowland rich-fen systems in England and Wales, to sample the range of vegetation-types present. Some 1500 releves was recorded. The data were classified using methods of cluster analysis (primarily information analysis), together with a computerized routine of traditional tabular sorting. The units generated by the analyses were incorporated into a hierarchical classification. Results are presented for the tall reed and sedge communities (Phragmition and Magnocaricion) of rich fens. Nine main syntaxa (Associations) are recognized: the Scirpo-Phragmitetum and Cladietum marisci, both widespread communities of swamps and wet fens; the Caricetum elatae, a localized community of topogenous hollows; the Caricetum paniculatae, a widespread but uncommon community of the margins of pools and lakes and of very wet fens; the Potentillo-Caricetum rostratae, widespread but local in topogenous hollows, and most characteristic of northern Britain; the Angelico-Phragmitetum, the most widespread and frequent tall reed and sedge community of lowland fens in England and Wales; the Cicuto-Phragmitetum, a rare community restricted to Broadland, Norfolk; the Peucedano-Phragmitetum, an important but local community of flood-plain mires, mainly in East Anglia; and the Cladio-Molinietum, a local community of valley fens, usually with a rather dry substratum. Also included are some species-poor communities effectively defined only by the dominant species. Some of the factors which may be instrumental in determining the composition of rich-fen communities are discussed. The importance of management regime and nutrient supply in influencing species-diversity is emphasized.