Intra-annual density fluctuations of Pinus pinaster are a record of climatic changes in the western Mediterranean region

Abstract

Climate projections for the Mediterranean area estimate a decline in total precipitation, warmer temperatures and a higher frequency of extreme drought events. It is important to understand how trees respond to these climatic changes and which wood anatomical structures best document the trees response to those changes. The present work investigates the climatic signal of tree-ring width (TRW), latewood width (LW) and the frequency of intra-annual density fluctuations (IADFs) during the last 100 years for Pinus pinaster Ait. growing in the Western Mediterranean region. Based on meteorological data it was observed that since the 1950s mean annual temperature and autumn and winter precipitation increased. TRW and LW of P. pinaster were positively correlated with winter and summer precipitation and negatively correlated with spring and summer temperatures. The frequency of latewood IADFs showed a positive and time stable correlation with September and October precipitation. However, after the 70s the frequency of IADFs became also correlated with climatic conditions latter in the year, specifically with the temperatures of November and December, probably linked to the recent climate changes. IADFs chronologies, besides being very useful to reconstruct autumn precipitation, they can add new climatic information to ring-width chronologies.