A clear long-term trend in climate change was identified. At all meteorological stations the air temperature increased during the last 20 years, and total precipitation started to increase 40 years ago. This is reflected in the radial growth increment of Siberian spruce and Scots pine. Thus, climate change could partly explain the increased site productivity.
The total variance explained by temperature varies from 26% to 48% and precipitation from 26% to 44%. The climate factors influencing increased radial increment of Siberian spruce differ from those in Scots pine. The higher temperatures allow enhancement of evapotranspiration, which is why both temperature and precipitation affected radial increment positively. The temporal stability of dendroclimatic relationships has changed for radial growth of Siberian spruces in western and eastern parts of Middle taiga zone. The statistically significant climatic parameters influencing radial increment of spruce and pine in Komi were identified. The increased radial increment of spruce and pine in Komi is attributed primarily to the increase in temperature. But the correlation of precipitation sums and air temperature with radial increment of Siberian spruce in Middle taiga zone changes over the time. Climate change is causing increasing site productivity, but its direct influence, identified by means of response function analysis, explains only part of the high frequency variations in radial increment. Taking into account the correlation with climate variables and their temporal stability, it is possible to simulate the future development of forest resources in Komi under the changing climate. For purposes of forest management, new climate-sensitive growth models should be developed.
This study was supported by a CIMO fellowship grant TM-04-2734, NorFA grant “Network for Dendrochronological Research in Northern Europe”, travelling grants from the Graduate School in Forest Sciences (University of Joensuu), the project Intensification of forest management and improvement of wood harvesting in North West Russia in the research programme Russia in flux funded by the Academy of Finland, Russian Foundation for Basic Research (project 06-04-48792). Thanks to Dr. Hans-Peter Kahle for critical comments that helped to improve this manuscript. Mekrijarvi Research Station provided excellent facilities for measuring the discs and cores from Russia. Dr. Bruce Miche helped improve the language of the manuscript.