Correlations between the Mn/Ca ratio in stemflow and epiphytic lichen abundance in a dieback-affected spruce forest of the Harz Mountains, Germany

Dieback-affected trees of a boggy stand of Picea abies in the Harz Mountains, northern Germany, bore a richer epiphytic lichen vegetation than healthy trees. Cover of the foliose epiphytic lichen Hypogymnia physodes decreased with increasing Mn/Ca ratio in stemflow. The total of lichen species per tree decreased both with the Mn/Ca ratio in stemflow and with the Mn concentration in bark. The results agree with experimental tests of Mn toxicity to H. physodes. Comparison with other dieback-affected spruce stands of the Harz Mountains revealed that Mn attained unusually high concentrations in the study site because of high Mn concentrations in the soil. Mn concentrations in soil, bark, stemflow, and incident precipitation suggest that Picea abies removes excess Mn taken up from the soil by the root system by transferring it into the bark. Mn in stemflow is supposed to derive primarily from leaching of Mn from bark and needles. SO42- concentration that was found to be decisive for epiphytic lichen distribution in other dieback-affected spruce stands of the Harz Mountains was of subordinate significance to lichen vegetation in the present case.