Decreasing abundance of epiphytic lichens with increasing Mn supply from the substratum or from stemflow was found in several coniferous forests of Europe (Germany) as well as western (Montana, British Columbia) and eastern North America (New York State). Experiments carried out with Hypogymnia physodes and other species of chloro- and cyano-lichens suggest that these correlations are causal. High Mn concentrations e.g. reduce chlorophyll concentrations, chlorophyll fluorescence and degrade the chloroplast in lichen photobionts. Excess Mn inhibits the growth of soredia of H. physodes and causes damage in the fine- and ultra-structure of the soredia. Adult lichen thalli remain structurally unaffected by Mn. Manganese uptake does not result in membrane damage. Calcium, Mg, Fe and perhaps also Si alleviate Mn toxicity symptoms in H. physodes. Lecanora conizaeoides is not sensitive to Mn in laboratory experiments or in the field. The data suggest that high Mn concentrations are an important site factor for epiphytic lichens in coniferous forests that until recently has been overlooked. Manganese reaching the microhabitat of epiphytic lichens is primarily soil-borne and is usually not derived from pollution.

Epiphytic lichen diversity in a boggy stand of Norway spruce (Picea abies) was studied in the eastern Harz Mountains, northern Germany. Spruce trees at wet sites were affected by forest dieback, whereas trees on drier sites remained unaffected. Lichen diversity was higher on diebackaffected trees than on healthy ones. The foliose lichen Hypogymnia physodes was significantly more frequent on dead trees, whereas the crustose, extremely toxitolerant Lecanora conizaeoides occurred more frequently on healthy trees. Stemflow concentrations of NH⊂4⊃+, NO⊂3⊃-, PO⊂3⊃-, and SO⊂4⊃2- were lower on affected trees. This is attributed to reduced interception from the atmosphere due to needle loss. Cover of H. physodes decreased with increasing mean SO⊂4⊃2- concentration in stemflow. The total of lichen species per sample tree also decreased with increasing SO⊂4⊃2- concentration in stemflow, indicating that most species reacted in a similar way as H. physodes. Cover of L. conizaeoides increased with increasing SO⊂4⊂2- concentration, but decreased at higher SO⊂4⊃2- concentrations. Bark chemistry had a minor influence on lichen diversity.