M nnipuistute radiaalkasvust muutuvates keskkonnatingimustes

The changes in the radial growth in two consecutive generations of pine stands was investigated. Two pure pine stands were selected for this study. The both stands were represented by two consecutive generations growing at the same location and in the same site conditions. The stands in Saaremaa are defined as Hepatica site type. The age of the older stand is 160 years and that of the younger stand is 55 years. The Tallinn stands are growing in the Rhodococcum site type. The age of the older and younger stands is 155 and 55 years, respectively. For determining the differences in the radial growth of successive stand generations the constant cambial age method was used. It consists of considering simultaneously, in the whole sample, the tree rings developed at a given cambial age but at various calendar years. The cambial age of a given tree ring is the age of the tree when this tree ring was built. In the present study the increment cores were taken at the height of 1.3 m. It was assumed that the pines reach this height in ten years. So the tree ring next to the pith at this height denotes the 11th year in the tree life. In analysis the average tree ring widths of stands at age of 30, 40 and 50 years was compared. The analysis showed that the radial growth of the younger stands at present exceeded that of the stands of old age when young. The difference in the average tree ring widths between young and old stands was greater in the case of the Saaremaa stands at each age compared than these of the Tallinn stands caused obviously by the more favourable site conditions of Saaremaa stands. These differences decreased with the increasing age of the stands. The main possible factors which may have caused changes in growth rates of stands at the present time are the deposition of the nitrogen, possible increase of CO2 in atmosphere and possible long-term changes of temperature among others. For the growth of the studied young stands, the increased N deposition and elevated CO2 level during the second half of the last century may have some positive influence, particularly in the case of the Tallinn stand, growing on the nutrient-poor sand soil. In Estonia, strong and significant relationships between the radial growth of pine stands and mean temperatures of the winter and early spring months has been detected by the earlier studies and as well by the given study. According to the observations made in the Tallinn-Harku meteorological station the average temperature of the winter months in 1950-2000 has increased by 1 °C compared to that in 1850-1900. Therefore it may be assumed that long-term continuous warming may cause the altered growth response of pines.