Dependence of tree ring stable isotope abundances and ring width on climate

Summary We measured ring widths and isotopic abun-dances of carbon, oxygen and hydrogen (δ13C, δ18O and δ2H) from the latewood of tree rings of pedunculate oak (Quercus robur L.) in its distributional northern limit in Southern Finland. Ring width was observed to be related to precipitation and relative humidity but not significantly to temperature. δ13C and δ18O were significantly related to all studied climatic variables, most strongly to cloud cover. Var-iations in δ2H were discovered to be complex combinations of signals from biochemical and physical processes. The re-sults suggest that oaks in Finland can be used as a source of climate information. δ18O was discovered to be especially promising as it showed the strongest climate signal and high-est common signal between trees. The relationship between climate and ring width indicates that water availability is the main control of ring radial growth. This is supported by the isotope data. High correlation between δ13C and δ18O time series indicates that photosynthetic carbon assimilation is limited by stomatal control. Therefore, in contrast to the expected temperature limitation, our data indicate that drought limits oak growth more than cold temperatures on the border of its northernmost distribution range