Annual Beech (Fagus sylvatica) Growth Rings and Solar-Related Climate Variations in the Central and Western Balkans in the 18th–21st Centuries

Abstract—This work analyzes a time series of annual growth ring widths for beech trees (Fagus sylvatica) in the western and central Balkans (Stara Planina, Bulgaria) to identify solar-related climate cycles. The effects of solar activity on beech growth during the Dalton Grand Solar Minimum (1793/98–1833) are studied based on samples ≥200 years of age. Two different methods (T–R periodogram analysis and wavelet analysis) are used to identify statistically significant variations with periods of 20–22, ~40, 60–70, and 210–220 years in most of the samples. Two samples are found to have a cycle of about 110 years. Statistically significant correlations between the ring widths and precipitation amounts and the temperatures from data of the nearest weather stations for 1899–2012 confidently manifest themselves in all four central Balkan samples and one western Balkan sample. Based on the results, it is concluded that a period of cooling and increased precipitation has likely begun in the climate of Bulgaria. The process is proceeding slowly, having begun approximately in 2007–2010, but it may noticeably accelerate after the end of solar cycle 25 and during cycles 26 and 27. It is concluded that cycle 26 is likely to be delayed in development. © 2019, Pleiades Publishing, Ltd.