Radial growth of conifers in regions of different cement dust loads

The climate–growth relationships and the variation of the radial growth of Oxalis– Myrtillus-site type Norway spruce and Scots pine stands in conditions of different cement dust loads were investigated. The climate–growth relationships were studied during the period from 1946 to 2004. The variation of the mean tree-ring width was studied during three time periods, from 1941 to 1965, from 1966 to 1991, and from 1992 to 2004, characterized by different dust pollution loads. For the investigation of the variations in radial growth during the succeeding time periods the average tree-ring widths were computed for each time period and these were compared with the average ring width in the first, 1941–1965 period. Dendrochronological methods were used. Two study sites, Kunda (2.5 km east of the emission source) and Malla (5.0 km east), are directly influenced by the dust emissions of a cement plant. Other two study sites, Eru (38 km west) and Revoja (34 km west), are situated on a relatively unpolluted area and served as control sample sites. The relationships between the radial growth and climate were almost similar on control and dust polluted sites. The climatic variables that had a significant effect on the radial growth of Norway spruce at both control and polluted sites were the temperature and precipitation of summer months of the current and preceding years. The pine stands growing under dust pollution were characterized by a significant positive impact of the current summer temperature on the radial growth. No precipitation variable having a significant effect on the radial growth of pines at all sites was found. The cement dust emissions had a small negative effect on the radial growth of spruce stands. A significant negative effect of the cement dust on the radial growth of pine stands during the period of large amounts of dust emission (1966–1991) was detected. The decrease in the dust emissions from 1992 improved the growth conditions at pine stand sites.