The effect of air-borne pollutants on the growth of Pinus sylvestris in the City of Oulu, Finland

Abstract

A study is made of the effects of emissions on the radial growth of Scots pines (Pinus sylvestris L.) growing in the vicinity of Kemira Chemicals Oy, established as Typpi Oy in 1951, in the city of Oulu. These effects are examined over the period 1950-1995 by comparing the tree-ring widths of the pines with data on air quality and climatic conditions. The radial growth of these pines is also compared with that of pines growing in two relatively clean areas, one 13 km and the other 45 km from Oulu. The fertilizing nitrogen dust emitted by the chemicals plant increased tree growth from the 1950’s to late 1960’s, after which radial growth decreased abruptly and remained low for about twenty years, due to toxic effluent from the plant. During that time the growth of the pines in the polluted area was markedly affected by winter temperatures, so that a cold winter would reduce their radial growth in the following summer and a mild winter improve it. In the 1990’s the radial growth of pines in Oulu has been faster than average, and also faster than in the reference areas or elsewhere in Finland, presumably as a result of (1) the improved quality of the air, (2) the old fertilizing effect, (3) improved conditions for the surviving trees, (4) elevated winter temperatures and (5) a heightened heat island phenomenon in the city of Oulu.