A decrease in the continentality of the Lithuanian climate is expected in response to climate change. Of all tree species, Norway spruce (Picea abies (L.) H. Karst.) is one of the most sensitive to changes in the climate. For this reason, studies on the crown condition of Norway spruce in different eco-climatic regions can help to identify factors that could have substantial effects on the condition of forests in the future. Data from Lithuanian regional forest monitoring (1989 – 2010) were used in this study. The crown condition of Norway spruce, the occurrence of defoliation and the proportion of healthy trees have been assessed annually for an average of 2,000 trees. Trends in the crown condition of spruce and the factors affecting spruce crown condition in three largest eco-climatic regions of Lithuania are presented in this paper as the Žemaičių Highlands, the Middle Plain and the South-East Highlands. A significant decrease in the crown condition of Norway spruce, caused primarily by Ips typographus damage (1993 – 1997), was recorded in all eco-climatic regions. After the elimination of the 1993 – 1997 data (I. typographus damage), the crown condition of Norway spruce showed a decreasing trend over the period of analysis. Crown defoliation increased (r= 0.66, p= 0.004), and the proportion of healthy trees decreased (r= -0.49, p= 0.02) in the coarse of time. The biggest Norway spruce crown condition decrease was observed in the Žemaičių Highland region – the most maritime climate region (Δ D = 4; Δ H = -14.5). The deterioration of spruce crown condition associated with the decrease of climate continentality may indicate that climate change is a possible factor influencing the degradation of the spruce crowns. Another potential driver for the decrease in spruce crown condition is the precipitation during the second half of the vegetation period.

Keywords: Norway spruce, defoliation, eco-climatic region, ICP-Forest