In 1985-99 studies were carried out in the area of the Kunda cement plant on North Estonian coastal plain on sample plots stretching 1.5 and 2.5 km east and 2 km and 3 km west, where changes in crown damages and radial increment of pine and spruce were estimated. The selected stands were with 0.7-0.8 density and II quality class, with moderately dense or sprase understorey, 75-85-year-old Myrtillus site type pine or spruce stands. Practically every tree in the area of intensive dust pollution had signs of damage. The relations between the defoliation and radial increment in the region were not linear. Weak defoliation (up to 25 per cent) influences slightly the radial growth. The correlations were more evident on Pinus sylvestris with more than half of the trees in the area having moderate or strong defoliation (at least 30-35 per cent). We suppose that defoliation, which leads to a decrease in the assimilating area of trees, causes essential changes in physiological processes. In the region of intensive pollution stress the radial increment decreased along with the defoliation level on both Pinus sylvestris and Picea abies

The research was conducted in 1990-99 in forest observation sites in the neighbourhoods of industrial enterprises of Kohtla-Jaerve-Johvi and the cement plant of Kunda and in the control area in Lahemaa National Park. Differences between the radial increments of conifers growing under pollution and in a relatively unpolluted area were estimated. The stands selected for investigation were similar as to their edaphic conditions and forest survey indicators. The high sensitivity of conifers to long term emissions of pollutants into the atmosphere from oil shale based power engineering and chemical industry, production of building materials and fertilisers and other industrial enterprises in the investigation area is expressed as changes in the radial increment of trees with the changes depending on the pollution load and alterations in precipitation and soil

Air pollutants (oil shale fly ash, gases, organic compounds) emitted by the oil shale industry in Kohtla-Jaerve, North-East Estonia, have caused changes in the growth conditions of forest ecosystems. Compared with the period before 1990 the pollution load in the area investigated has fallen drastically; however, this has not resulted in an essential improvement in growth conditions of trees. Morphological analysis of 80-year-old Picea abies (L.) Karst. and Pinus sylvestris L. growing on sample plots (6) in the polluted area and in the control area showed that air pollution has had a temporally and spatially variable effect on the parameters characterising the state of trees: length growth, weight and dry matter content needles and shoots, density of needles on shoots and radial increment of trees. The length growth of Scots pine needles and shoots proved to be one most suitable parameters indicating the influence of air pollution, although not in all sample plots investigated. The results for fresh and dry weight of needles revealed great differences between sample plots. The biomass of the shoots of Norway spruce was notably greater in the immediate vicinity of Kohtla-Jaerve than in the control. The Scots pines and Norway spruces whose shoots showed inhibited length growth had greater density of needles on shoots with difference from the control being respectively up to 33 per cent and 16 per cent. The effect on the radial increment of Norway spruces was especially strong in the immediate vicinity of pollution sources but it fell rapidly with distance from them

A needle trace method was used to reveal the chronology of needle retention and growth rates on Scots pine in a stand near a power plant operating on oil shale. During the period of 1964-97, the height increment varied between 31 and 64 cm yr (-1), and the radial increment ranged from 1.06 to 3.71 mm yr (-1). The average needle density on the newly sprouted shoots of the main stem was 5.9 needles cm (-1) and the mean needle production on the same shoots was 266. The average number of needle sets along the main stem ranged from 2.2 to 3.1, the mean age of needles varied between 1.3 and 2.3 years. The short-term maximum concentrations of oil shale fly ash and SO2 ranged from 55 to 2510, and from 75 to 270 micro g m (-3), respectively. The annual average concentrations of fly ash varied between 6 and 95 micro g m (-3), and of SO2 between 2.5 and 10 micro g m (-3). Changes in neither the concentrations of fly ash nor SO2 were associated with the variation in needle retention of Scots pine. In the case of height increment, however, the correlation with the annual average concentration of oil shale fly ash was significant (r=0.83; p0.05)