Vitas, A. and Žeimavičius, K. 2006.Trends of Decline of Douglas Fir in Lithuania: Dendroclimatological Approach. Baltic Forestry, 12 (2): 200-208

Dendroclimatological research on Rocky Mountains Douglas fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and Green Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) - introduced trees in Lithuania has been discussed in the article. Multiple regression analysis has shown positive and significant influence of air temperature at the end of winter - beginning of spring on the radial growth of Douglas fir, while the strong positive impact of precipitation in June prevails in eastern Lithuania. Analysis on pointer years of the radial growth has indicated that decreases in the radial growth of Douglas fir are driven by colds in winter - spring and droughts in summer. Increases in the radial growth are connected to warm winters and humid summers. Our research indicates that the importance of winter colds as the limiting factor for the radial g rowth of Douglas fir at the end of the 20th century has decreased, while summer droughts gain greater importance. According to the trends on the global climate change it is supposed that summer droughts will remain the main limiting factor for the survival of Douglas fir in Lithuania in the beginning of the 21st century. Conditions more favourable for the growth of Douglas fir are likely to be in the regions of West Lithuania: seaside lowlands and Žemaičiai Uplands.

Key words: climate, Green Douglas fir, pointer year, radial growth, Rocky Mountains Douglas fir