Ranunculus hederaceus L. as indicator of land use changes in The Netherlands

In The Netherlands Ranunculus hederaceus is a rare species that occurs in running waters. It appears to be confined to zones with a constant supply of mineral-poor groundwater, originating from highly fertilized fields. The relation between species performance and chemical composition of the water was investigated by means of response analysis. No relation was found unless the mineral content of the water was multiplied with stream velocity (yielding a measure for mineral supply per time unit). In the latter case significant correlations were found for calcium, bicarbonate, sodium, chloride and sulphate. We discuss whether low P-availability in the system could limit biomass production of Ranunculus hederaceus, although this appeared to be unlikely. Competition for light with algae and large helophytes is more likely to be a major reason for the absence of the species in stagnant waters. The situation near Oudemolen illustrates the indicative value of the species. Detailed investigations showed that artificial drainage changed the original mesotrophic conditions into eutrophic circumstances, which are much more favourable for this species. Hence, the increase of a rare plant species like Ranunculus hederaceus does not always indicate the well-being of a nature reserve.