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Heavy metals and sulphur have been emitted from the Cu-Ni smelter at Harjavalta since 1945. This article reviews the work that has been published in scientific journals after 1975 concerning heavy metal deposition and the effects of pollution on forest ecosystem around Harjavalta. The pollution has had diverse effects on boreal forest ecosystem, e.g. vegetation, nutrient cycle mediated by microbiota and soil animals, herbivorous insects and pathogens, resistance mechanisms of vegetation, and birds. The deposition of heavy metals has increased up to 30 km distance from the smelter. At 8 km distance the ecosystem began to approximate an undisturbed ecosystem where only slight changes in the understorey vegetation were observed. At 4 km distance the species composition of different ecosystem components (vegetation, insects, birds, soil microbiota) had changed and the growth of trees was retarded. At 0.5–1 km distance, where the nutrient cycling was disturbed and only the most resistant organisms were surviving, the ecosystem had ceased to carry out its essential functions. Remediation through liming or mulching with organic matter, of forest soil has had some positive effects on the ecosystem.