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, latewood width, and the frequency of intra-annual density fluctuations (IADFs) during the last 100 years for Pinus pinaster Aiton growing in the western Mediterranean region. Based on meteorological data, it was observed that since the 1950s, average annual temperature and autumn and winter precipitation increased. Tree-ring width and latewood width 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 1970s, the frequency of IADFs also became correlated with climatic conditions later in the year, specifically with the temperatures of November and December, probably because of the recent climate changes. IADFs chronologies, besides being very useful to reconstruct autumn precipitation, can add new climatic information to ring-width chronologies.