Amelioration and restoration of Scots pine stands close to the Harjavalta Cu-Ni smelter in SW Finland John Derome 1 , Hannu Fritze 2 , Heljä-Sisko Helmisaari 2 , Oili Kiikkilä 2 , Mikko Kukkola 2 , Eino Mälkönen 2 , Tiina Nieminen 2 , Anna Saarsalmi 2 and Maija Salemaa 2 1 Rovaniemi Research Station, The Finnish Forest Research Institute, P.O. Box 16, FIN-96301 Rovaniemi, Finland 2 Vantaa Research Centre, The Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, Finland Corresponding author: John.Derome@metla.fi Abstract Although emissions of SO 2 and heavy metals from the Cu-Ni smelter at Harjavalta, SW Finland, have been strongly reduced in recent years, the topsoil of neighbouring forested sites still contains 50 years’ accumulation of a wide range of heavy metals. Scots pine stands growing close to the smelter are suffering from serious defoliation and growth retardation, and microbial activity and mineralization in the forest floor are strongly retarded. A severe shortage of plant-available nutrients in the organic layer is accompanied by relatively high levels of immobilised macronutrients (e.g. Ca, Mg) in the organic layer. In order to alleviate and counteract the detrimental effects of heavy metal accumulation on stand health and vitality, the Finnish Forest Research Institute has established a number of field experiments with correction fertilizers, liming and the addition of an organic mulch (municipal compost/wood chips) to the forest floor. The effects of the treatments on tree growth, needle biomass, needle nutrient status, litterfall, fine root formation, deposition chemistry, soil microbial activity and community structure, and soil and soil solution quality were monitored during the latter half of the 1990’s. Correction fertilization with a mixture of slow- and fast- release mineral nutrients (excluding N) and liming had a positive effect on soil and soil solution chemistry, and on fine root growth, but relatively little effect on the growth and nutrient status of the tree stand. In most parts of the pine stands the forest floor is completely devoid of ground vegetation, and the addition of an organic mulch has had an extremely positive effect on recolonisation of the site. The organic mulch has also considerably increased the concentrations of macro- and micronutrients in the soil solution. Background Copper and nickel are produced at the Harjavalta smelter in SW Finland by the flash- smelting pyrometallurgical process in two separate smelters. Copper smelting first started in 1945, a sulphuric acid plant was built at the site in 1947, and nickel smelting started in 1959. The copper and nickel ores smelted at the plants contain sulphur, heavy metals and arsenic. Emissions during the period from the founding of the smelters up until the end of the 1980’s were relatively high, and comprised gases (SO 2 ) and particulate material, mainly consisting of Fe, Cu, Ni, Zn, Pb, Cd and As. Although emissions of SO 2 and heavy metals from the Cu-Ni smelter at Harjavalta have decreased considerably since the early 1990’s as a result of the construction of a new, taller stack and installation of modern filters, the topsoil of neighbouring forested sites still contains 50 years’ accumulation of a wide range of heavy metals. Scots pine stands growing close to the smelter are suffering from serious defoliation and growth retardation, the needles have low nitrogen and especially magnesium concentrations (Derome & Nieminen 1998), fine root mortality is high (Helmisaari et al. 1999) (Fig. 1), the understorey vegetation in the stands has been almost completely destroyed (Salemaa et al. 2001), there is considerable accumulation of undecomposed needle and other plant litter on the forest floor (Fritze et al. 1989), microbial activity and mineralization in the forest floor are strongly retarded (Fritze et al. 1996), the soil bacterial community has become adapted to the elevated heavy metal concentrations