The Carex flora of varied landscapes in The Netherlands: an example of decreasing ecological diversity

The Carex floras of five inland landscapes in The Netherlands {fig. I) are compared to each other, with emphasis on phytogeographical, syntaxonomical and ecological aspects (table I). Moreover, changes in the distribution frequencies of the Carex species have been analysed by comparing two sets of frequency data to each other (census periods 1900-1949 and 1950-1975; cf. table 3). A strong decrease is noticed in many species: both in species occurring in The Netherlands at the margin of their phytogeographical range and in species occurring near the central parts of their range (table 4). In relation to habitat (table 5) little decrease is found in the species groups of dynamical and eutrophic environments; on the contrary, a dramatic decline can be observed in many species associated to complex, stable (semi-) natural habitats (e.g. Carex dioica ■fig-2). It is argued, that the real decrease of many Carex species is much more severe than is indicated by the current census methods. At least 20 out of the 59 species of the Netherlands Carex flora are threatened to such an extent, that probably they will only survive in a (very) few fitting Nature Reserves. The impoverishment of the Carex flora significantly reflects the recent changes in the Dutch flora as a whole. The high indicator value of Carex species makes their disappearance the more regrettable from a scientific point of view.