Climatic sensitivity of δ13C in tree rings of Quercus robur L., Populus tremula L. and Pinus sylvestris L. in Vilnius region (eastern Lithuania)

The aim of this work was to evaluate the possibilities of using carbon isotope measurements to determine a strong climate signal of trees influenced by the pollutant stress as well as to examine the difference in reaction of several investigated species to the climate change. Eurasian aspen (Populus tremula), pedunculate oak (Quercus robur) and Scots pine (Pinus sylvestris) trees from Vilnius region were selected for the stable carbon isotope analysis. Our results showed that over the last 70 years (1940-2009) the climate during summer months was the most important factor for the variation of stable carbon isotope values in tree rings, but its influence on different tree species slightly differed. delta C-13 measurements in Eurasian aspen best corresponded to the air temperature and the precipitation signal in July-August. Oak was more sensitive to the temperature and relative humidity in June-July. A positive correlation coefficient with temperature in the period of transition from the previous vegetation to dormancy season (previous September-October) was specific to oak as well. Scots pine grown at a polluted site was sensitive only to precipitation in summer months of the growing season. The correlation between delta C-13 measurements and climate data was determined to be from low to moderate in all the investigated trees and did not exceed the value of |r| >= 0.71 suggested by McCarroll et al. (2003) as a necessary value for the reliable climate reconstruction. However, the highest correlation coefficient values of 0.65 and 0.61, obtained between the maximal air temperature throughout the hydrological year (previous September-current August) and d13C in oak rings or between mean monthly sunshine hours throughout July-August and delta C-13 values in aspen rings, respectively, are comparable with those used in many palaeoclimatic reconstructions that were based even on weaker correlations.