Which matters most for the formation of intra-annual density fluctuations in Pinus pinaster: age or size?

A new method is pro posed to standardize chronologies of intra-annual density fluctuations to improve their intra-annual climatic signal. In the Mediterranean area, intra-annual density fluctuations (IADFs) are triggered by short-term climatic variations during the growing season. It is known that the formation of these anatomical structures is dependent on age and size, which can represent a problem during the extraction of the environmental signal from IADF chronologies. We present a new method using a two-step approach to remove the effect of tree-ring width from IADF chronologies. The climatic signal of IADF chronologies obtained by the proposed method was compared with previous methods, using 160 Pinus pinaster tree cores from an even-aged stand on the west coast of Portugal. Our results show that the climatic signal of IADF chronologies was strongly affected by the standardization method used, and that it could be improved by removing the effect of the predisposing factors (cambial age and tree-ring width) on IADF formation. Moreover, additional climatic information (previous winter precipitation) was only revealed when the effect of tree-ring width was removed from IADF series. Finally, we propose that this new method should be tested for other species and across larger geographical areas to confirm its capacity to remove noise from IADF chronologies and to improve their intra-annual climatic signal.