Lichen richness-biomass relationship in terricolous lichen vegetation on non-calcareous substrates
Bültmann, Helga; Daniels, Fred J. A.
Lichen richness-biomass relationships were studied in 286 plots of 50 cm x 50 cm in terricolous lichen vegetation on non-calcareous substrates of temperate northern Germany (64 plots) and Denmark (49), boreal Finland (75) and low-arctic Southeast Greenland (98). Frequency and magnitude of disturbance were estimated for each plot. Syntaxonomically the stands belong to the Ceratodonto-Polytrichetea, Peltigeretalia and represent 5 federations: Baeomycion rosei, Cladonion arbusculae, Cladonion rei, Solorinion croceae and Cetrarion nivalis. Lichen richness clearly increases from temperate to low-arctic regions. Highest biomass values are achieved in boreal Finland. The biomass values include lichens and bryophytes. For the temperate and boreal study areas the relationships principally agree with those predicted by Grime's humped-back model. The relationships seem to be primarily determined by the gradient of anthropo-zoogenic disturbance because most stands belong to the same successional series. In low-arctic Southeast Greenland the lichen richness-biomass relationship is much more complicated, probably due to the fact that lichen vegetation can occur in much more different habitats. This results in more different gradients of stress and disturbance. The relationship mainly differs in two aspects. On the one hand lichen richness at intermediate biomass values can not only be high, as expected from the model, but also quite low (less than 10 species / 0.25 m2). The very low lichen richness at intermediate biomass values appears to be correlated with prolonged snow cover. On the other hand the decrease in lichen richness at high biomass values is much less pronounced in the Low-Arctic than expected. This is probably due to a declining competitiveness of the large species caused by stress combined with the omnipresent small-scale disturbance in the Arctic.