Site conditions influence the climate signal of intra-annual density fluctuations in tree rings of Q. ilex L.

Key Message: The investigation of the relations between climate and intra-annual density fluctuation (IADF) traits (e.g. frequency, width and functional anatomical traits) inQuercus ilextree rings of stands living on two opposite slopes, highlighted the influence of local site conditions on the climate signal contained in tree rings. Moreover it allowed to identify the main site-specific environmental drivers for IADF formation. Context: Wood functional traits such as IADFs result from the adaptation of tree physiological processes to seasonal climate variability. They could be used to reconstruct tree response to intra-annual variations in environmental conditions. Aims: We investigated the relationship between IADF features and climate in Quercus ilex L. populations living on opposite slopes, aiming to evaluate the influence of local site conditions on wood plasticity in response to seasonal climate variability. Methods: Dominant trees were sampled and dated. IADF frequency and width, non-lumen fraction, vessel size, and frequency were measured. Time series analyses using precipitation and temperature data were performed. Results: A decrease in IADF frequency over time influenced by summer and autumn temperature was observed at both sites. IADFs were more frequent, wider, with smaller vessels and a higher non-lumen fraction in trees growing at the north slope compared to the south slope site. IADF anatomical parameters of south slope tree rings were mainly influenced by precipitation, while the ones of north-slope tree rings by temperature. Conclusion: Temperature-limited IADF occurrence in Q. ilex tree rings, probably leading to an earlier stop in cambial activity, and IADF anatomical traits were influenced by site conditions, suggesting them as indicators of site-specific responses to climate.