Tree mortality episodes in the intact Picea abies-dominated taiga in the Arkhangelsk region of northern European Russia

Question What were the temporal patterns and rates of tree mortality in a recent episodic tree mortality event? Have similar events occurred in the past, and does climatic variability play a role in the disturbance regime? Location Intact Picea abies-dominated taiga in the Arkhangelsk region, northwestern Russia. Methods We reconstructed the past tree mortality and disturbance history by applying dendroecological methods in five forest stands and related these to climatic data. The role of other potential causes of tree mortality was assessed in a field inventory. Results The recent episode lasted from 1999 to 2004, influenced all stands studied, and killed on average 21% of trees with a diameter of over 10 cm at 1.3-m height. The annual tree mortality rate in the decades preceding this episode was 0.49%. During the past 200 years, the stands have experienced chronic small-scale disturbances, with several irregular disturbances of moderate severity. The recent episode was associated with abundant signs of the bark beetle Ips typographus. Furthermore, the timing of both the recent tree mortality episode and the past disturbance events was associated with dry summers. Conclusion The results indicate a connection between climatic variability and forest dynamics, the likely driving factors being droughts and bark beetles. In the context of the past 200 years, the recent episode was potentially at the higher end of the range of disturbance variability in terms of severity and spatial extent. This has ecological implications in a changing climate, potentially influencing ecosystem structure and long-term dynamics.