Edaphic relationships among Cirsio-Molinietum and related wet grassland communities in lowland Wales

Soil properties are characterized for a range of the Molinietalia vegetation types in lowland Wales. In this oceanic region there is overlap in the distribution of various forms of wet pasture dominated by Molinia caerulea and Juncus acutiflorus. There is subtle and continuous variation in species composition among four communities investigated; this has been analysed by Detrended Correspondence Analysis and partitioned between subcommunities recognized in Rodwell (1991). Canonical Variates Analysis indicated that the main differences in soil conditions between the vegetation classes are related to gradients in base-status; apparent variation in soil fertility may also be significant and requires further investigation. In general, Molinia-Cirsium dissectum fen-meadow soils have higher pH, higher Ca-levels, greater base saturation and lower acidity than Molinia-Potentilla erecta wet grasslands; those of Juncus-Galium palustre rush-pasture and Molinia-Crepis paludosa mire had relatively high levels of inorganic N. The findings are discussed with reference to ecological and phytosociological relationships, and also in the context of nature conservation.