Roadside Scots pine as an indicator of deicing salt use - A comparative study from two consecutive winters

The accumulation of salt and visible injuries on Scots pine needles (Pinus sylvestris) were investigated in a field study during two years 1992-1994. Two sampling plots 4 km apart along the highway 9 in eastern Finland were s elected. At Savo-Karjala region, the use of road salt was reduced to about one tenth from normal (slightly salted site), whereas, the use of road salt continued normally at the Central Finland region (heavily salted site). Cu rrent, one-year and two-year-old needles were sampled eight times during ye ars 1992-1994. Visible injuries in the pine needles were recorded and sodiu m, chloride and calcium concentrations analysed. During the two-year study, reduced use of deicing salt clearly reduced the accumulation of salt compo nents, sodium and chloride, and induction of visible injuries in the pine n eedles growing closest to the roadside. No changes in needle calcium concen trations were observed. In the sampling plot along the heavily salted site, browning and premature needle loss was detected especially during late spr ing. Deleterious effects of road salt did not reach far from the road, sinc e at distances of 20 to 30 m, the salt concentrations and visible injuries in needles were insignificant. Since no changes in soil salt concentrations between sites were observed, aerial salt spray is considered more importan t to salt accumulation in needles than root uptake. The changes in weather conditions have a significant effect on the accumulation of salt in needles and occurrence of the visible injuries. Great fluctuations in temperature and salt use during winter exacerbate the needle injuries. Thus, the salt c oncentrations and visible injuries caused by such concentrations of salt sh ould always be considered with respect to the climatic conditions.