Diversity of vegetation with Carex chordorrhiza L.f. and factors affecting the species abundance across its geographical range in Europe

Abstract

Species abundance is believed to be connected with geographical distribution and to decrease from central towards marginal parts of the distribution range. We investigated the cover-abundance of Carex chordorrhiza within varied plant communities reported from Europe, and with features that may influence sedge abundance in the ‘within’ and ‘outside’ areas of the species core range. Carex chordorrhiza is a small boreal sedge with a geographical range declining from north and north-eastern Europe towards the southwest. In all European countries outside its core range, string sedge is classified under various threat categories. The phytocoenotic amplitude of the species, established on the basis of 586 phytosociological relevés, was wider than previously described. Carex chordorrhiza was recorded in both treeless and wooded plant communities, representing five classes and 18 alliances, although Scheuchzerio–Caricetea fuscae was confirmed to be the central class. Species cover-abundance in most cases did not exceed 25% of the relevé area, indicating that the plant is a rare species that is only locally abundant in specific habitats. Ecological amplitude, based on Ellenberg’s mean indicator values, was also comparable in marginal and central parts of the range and was widest in the case of soil reaction and narrowest in the case of nitrogen availability. The generalized linear model established for communities of Scheuchzerio–Caricetea showed that the cover- abundance of Carex chordorrhiza increased significantly with increases in the mean values of light and nutrient availability and was higher in the marginal part of the geographical range, particularly in communities dominated by brown mosses and low herbs. The abundance of Carex chordorrhiza, at least in the European part of its geographical range, does not confirm the ‘abundant-centre’ hypothesis pattern.