Changes in climate-growth relationships and IADF formation over time of pine species (Pinus halepensis, P. Pinaster and p. sylvestris) in Mediterranean environments

Background: The Mediterranean basin has experienced an increase in the mean annual temperature, a decrease in the mean annual precipitation, and an increase in the frequency of severe drought periods during the second half of the 20^th century. However, winter and spring precipitation has increased and summer precipitation has decreased in the western Mediterranean region. Aim of the study: The objectives of the present study were: i) to compare changes in climate-growth relationships over time for Pinus halepensis, P. pinaster and P. sylvestris in Spain ii) to quantify the presence of intra-annual density fluctuations (IADFs) on the three species, and iii) to define the associated climatic variables. Area of study: 26 sampling sites (8 P. halepensis sites, 8 P. pinaster sites and 10 P. sylvestris sites) were selected in their distribution area in Spain. Main results: Precipitation is the main factor influencing growth and IADF occurrence in the three species. Wet periods during previous winter and spring induced higher growth rates on P. halepensis and P. pinaster, while P. sylvestris was mostly influenced by summer precipitation. However, the influence of these climatic variables on the growth of these species changed over the studied period. The increase of winter and spring precipitation combined with increasingly harsh summer climatic conditions in the second half of the 20^th century may have enhanced the importance of precipitation at the beginning of the growing season on the growth of species subject to higher summer drought stress (P. halepensis and P. pinaster) and increased IADF occurrence. Research highlights: Besides reflecting changes in the environmental conditions during the growing season, the inclusion of IADF detection in chronologies adds new information to ring-width chronologies, thereby improving its quality.