Long-term emissions of calcium-containing dusts from an iron factory influenced soil pH, vegetation and perhaps contributed to the capercaillie Tetrao urogallus decline in the study area in eastern Germany. Dramatic changes of the ground vegetation were observed in time (vegetation analyses in 1956, 1965, 1983 and 1990–1993) and along the pH-gradient. Near the emission source the mean number of plant species has increased from 15 to 65 since 1956. Ericaceae (Vaccinium myrtillus, V. vitis-idea, Calluna vulgaris), which are essential to capercaillie for food and cover, were replaced by Senecio fuchsii, Digitalis purpurea, Dactylis glomerata, Calamagrostis epigeios, Rubus idea, Myringia trinerva, and Urtica dioica. The decline in capercaillie numbers was correlated with the eutrophication effects of the emissions as measured by the increase of plant species diversity. Increasing plant species diversity may also favour small rodents and thereby the density of predators (such as the red fox Vulpes vulpes and wild boar Sus scrofa), as indicated by the increased hunting bags. Therefore, the increased predation on capercaillie nests and chicks that was documented on the study area over time may be a secondary effect of air-borne pollution.