Growth variation of Scots pine across a pollution gradient on the Kola Peninsula, Russia

Decadal exposure to emissions from a non-ferrous smelter has damaged the forest ecosystems surrounding the city of Monchegorsk located on the Kola Peninsula in northwestern Russia. We use the methods of tree-ring analysis to study the areal extent and timing of recent growth reductions of Scots pine (Pinus sylvestris L.) in the region surrounding the smelter in Monchegorsk. Reduced growth of Scots pine was observed up to 30 km southwest of the smelter. This directional gradient of forest damage is related to the dispersal of pollutants which is influenced by the prevailing northern winds and local topographic features. Old Scots pines (age 200 years +) appeared to be more sensitive than younger ones: growth reductions of old trees had started earlier and reductions were observed farther from the smelter than for younger trees. The findings are compared to a classification which describes the state of forest ecosystems based on the occurrence of certain plant species; the classification matched well with the observed growth trends. Pollution-induced changes in the climatic signal in tree-rings are also studied. The strong dependence of growth on mid-summer temperatures, typical for Scots pine on high latitudes, proved to be insensitive to effects of pollution. Changes in the climate-growth relationship took place decades after growth trends had started to decline.