Growth patterns of Scots pine (Pinus sylvestris L.) under the current regional pollution load in Lithuania

Abstract: The belief that trees have begun growing more rapidly in recent years was examined in Scots pine (Pinus sylvestris L.) forests, a dominant forest type in Lithuania. The largest, pre-dominant pine trees, with a diameter at breast height exceeding 50 cm, were selected for analysis in this study; these were growing in three experimental overly-mature stands located in different parts of Lithuania (north-eastern, western and seaside). We hypothesized that if the annual tree increment has increased in recent years, then the largest trees in the stand should regularly demonstrate this characteristic first of all. The data collected for this study confirmed that since the 1980 growing season the annual increment of the pine trees analysed here has increased. The causes of this rapid growth were higher air temperatures during the dormant period and, to a lesser extent, the higher temperatures from May through August. The effect of precipitation was negligible. A 30-year long data set on acidifying pollutants allowed us to detect significant effect of reduced SO2 concentration and sulphur deposition as well as gradually increased ammonia deposition on the increased annual basal area increment of pine trees over the last 30 year long period. Multiple regression analysis indicated that meteorological parameters can explain up to 50% of the observed increase in the growth rate of Scots pine in Lithuania; meanwhile the presence of acidifying species can account for an additional 30%. However, the pollution data set (20-30 years) was insufficiently long to be compared with the meteorological data. Therefore we were unable to distinguish whether the recent decrease in pollution or global warming resulted in the increases in tree growth rates more significant.