Oligotrophic and mesotrophic vegetation in southern Scandinavian mountains. Gradients in species and community distribution extracted by numerical analyses of earlier published vegetation descriptions
Fennoscandian mountain vegetation and its ecology has been a field of intensive research for more than a century, and the main aims of the studies have in most cases been to perform regional vegetation descriptions with subsequent phytosociological classifications. The main patterns in species distribution and vegetation composition along important ecological gradients are therefore well known, but so far no generally accepted classification of mountain vegetation has been reached. The present study is based on a compilation of 306 oligotrophic and mesotrophic communities (with data from more than 2200 stands and 4800 relevés) from the Scandinavian mountains. The sampling unit used here is the described plant communities, and an importance value (IV) is calculated for all species (taxa) based on their frequency and mean cover. The main aims were: (1) to quantify similarities and dissimilarities between earlier described mountain vegetation communities by use of numerical methods, (2) to discuss the results in relation to earlier proposed classifications of Scandinavian mountain vegetation, and (3) to interprete the main gradients in the data. DCA axis 1 (5.04 SD units long with an eigenvalue of 0.60) was interpreted to represent a complex gradient with increasing length of snow cover, soil moisture and altitude. DCA axis 2 describes a complex gradient in soil thickness, soil moisture and altitude. Eighteen groups of communities were separated by TWINSPAN, and these are discussed in relation to earlier classifications. Most of these groups have some overlap in the ordination diagram, indicating that the communities make a continuum. Along the main gradient, three community clusters could be separated: (1) communities dominated by lichens and ericaceous species; (2) fern-, graminoid- and Salix herbacea-dominated communities; and (3) extreme moss-dominated snow beds.