Summer temperature variations reconstructed by tree-ring data at the polar timberline in Siberia

This paper discusses preliminary results of a dendroclimatic study in the subarctic regions of Siberia and the Far East, along a transect 4500 km long. Ring-width chronologies were developed using living coniferous trees. The chronologies range from 227 to 612 yr in length and most contain a very strong climatic signal, mainly of June and July temperatures of the growth year. A similar variability of index values within large areas (up to 800 km) along the transect was observed. The territory studied was divided into four dendroclimatic regions using threshold values of the coefficients of correlation (>0.4) between chronologies and synchronization of growth indices (>68%) and by comparison with the spatial variations of the first eigenvector of growth indices. Seven types and fifteen subtypes of growth index changes along the transect in separate calendar years were determined. Variability of reconstructed summer temperatures is very high (year-by-year range is up to 5.0-6.3 degrees C). There is no evidence of increasing trend in tree growth during the last few decades that could be connected with anthropogenic climatic changes in summer months.