Roadside Scots Pine as an Indicator of Deicing Salt Use – A Comparative Study from Two Consecutive Winters

Abstract

The accumulation of salt and visibleinjuries on Scots pine needles (Pinus sylvestris) were investigated in a field study duringtwo years 1992–1994. Two sampling plots 4 km apart alongthe highway 9 in eastern Finland were selected. AtSavo-Karjala region, the use of road salt was reducedto about one tenth from normal (slightly salted site),whereas, the use of road salt continued normally atthe Central Finland region (heavily salted site).Current, one-year and two-year-old needles weresampled eight times during years 1992–1994. Visibleinjuries in the pine needles were recorded and sodium,chloride and calcium concentrations analysed. Duringthe two-year study, reduced use of deicing saltclearly reduced the accumulation of salt components,sodium and chloride, and induction of visible injuriesin the pine needles growing closest to the roadside.No changes in needle calcium concentrations wereobserved. In the sampling plot along the heavilysalted site, browning and premature needle loss wasdetected especially during late spring. Deleteriouseffects of road salt did not reach far from the road,since at distances of 20 to 30 m, the saltconcentrations and visible injuries in needles wereinsignificant. Since no changes in soil saltconcentrations between sites were observed, aerialsalt spray is considered more important to saltaccumulation in needles than root uptake. The changesin weather conditions have a significant effect on theaccumulation of salt in needles and occurrence of thevisible injuries. Great fluctuations in temperatureand salt use during winter exacerbate the needleinjuries. Thus, the salt concentrations and visibleinjuries caused by such concentrations of salt shouldalways be considered with respect to the climatic conditions.