VARIATION IN HABITAT FACTORS AND SPECIES COMPOSITION OF SCORPIDIUM SCORPIOIDES COMMUNITIES IN NW-EUROPE

To assess the natural range in habitat parameters of the once common r ich-fen bryophyte Scorpidium scorpioides, water chemistry and vegetati on were studied in different regions characteristic of its NW-European distribution area: the Netherlands, Ireland, Denmark and Fennoscandia . Scorpidium scorpioides was found in an environment with circumneutra l pH. The variation in solute content and composition was large and nu trient (N and P) concentrations ranged from zero to values indicative of more eutrophic conditions. Six different vegetation types with S. s corpioides were distinguished, resembling Caricion davallianae, Carici on curto-nigrae and Hydrocotylo-Baldellion communities. Type of substr ate and solute levels were strongly correlated with the first ordinati on axis (DCA) and nutrient status and geographic position with the sec ond axis. Habitat and vegetation characteristics in Dutch rich-fens wi th S. scorpioides indicated that mineral status was higher than in Fen noscandia and Ireland; solute-poor habitats with S. scorpioides have d isappeared from the Netherlands. Trophic status was higher in the Neth erlands than in Fennoscandia, but in some cases lower than in Ireland. Acidification and eutrophication may have played a role in the decrea se of the species in the Netherlands. However, the wide ecological ran ges su that the decrease of S. scorpioides is not a physiological effe ct of unsuitable environmental conditions per se.