Syntaxonomy of arctic terricolous lichen vegetation, including a case study from Southeast Greenland

Combinations of cryptogam species are classified in a distinct synsystem of microcommunities and can be described according to the Code of Phytosociological Nomenclature. The units, microcoena, can occur in more than one phytocoenon and often have larger distribution areas than phytocoena. Microcoenoses are often of small extent (less than one square metre), but can cover vast areas in the Arctic. Microcoena mainly reflect microhabitat factors, and can therefore be useful tools to screen or map the complexity of vegetation and landscape on a smaller scale. The methods and advantages of a layered microcoenon-phytocoenon approach are discussed. A detailed study of terricolous lichen-rich vegetation from Southeast Greenland presents 22 microcommunities, their habitats, relations to phytocoena and species richness. Results of a canonical correspondence analysis showed snow cover duration and wind exposure as main factors determining floristic composition of the microcoenoses in the study area. Microcommunities of the alliance Solorinion croceae often occurred in phytocoenoses of the class Salicetea herbaceae and those of the alliance Cetrarion nivalis in phytocoenoses of the class Loiseleurio-Vaccinietea. Microcoenoses of the alliance Cladonion sylvaticae in communities of the classes Salicetea herbaceae and Loiseleurio-Vaccinietea indicated less extreme habitats. An example of a more detailed characterization of phytocoena by microcoena and vice versa is given for the microcoenon Cladonietum mitis and the phytocoenon Caricetum bigelowii. Species richness was often rather high (up to 47 lichens and 71 plant species in a plot of 0.25 square metre) and seldom very low. This indicates decreasing impact of competition in arctic lichen vegetation and increasing impact of, however non-extreme, disturbance and stress. The lichen-rich microcoena found during the field study and those having been reported from the Arctic before are compiled and discussed.