Stemflow chemistry and epiphytic lichen diversity in dieback-affected spruce forest of the Harz Mountains, Germany

In the German Harz Mountains, epiphytic lichen diversity was found to be higher in a Picea abies forest affected by pollution-caused dieback than in a comparable healthy stand. Although amount and chemical composition of incident precipitation did not differ between the stands, element concentrations of S, H+, K, Fe, Mn, and Al in stemflow were significantly lower in the dieback-affected plot than in the healthy one. These lower concentrations are attributed to reduced interception and reduced leaching due to needle loss. Cover of Hypogymnia physodes decreased with increasing concentrations of many elements in stemflow and bark. Among these parameters, S concentration of stemflow is considered to influence directly H. physodes. Cover of the extremely toxitolerant Lecanora conizaeoides was less affected by chemical variables, but a significant dependence of cover on S concentration of stemflow, resulting in an optimum regression curve, could be established in this case. Total number of lichen species per sample tree decreased as concentrations of several elements increased, indicating that most lichen species had similar habitat requirements as H. physodes.