Olive tree-ring problematic dating: a comparative analysis on Santorini (Greece)

Olive trees are a classic component of Mediterranean environments and some of them are known historically to be very old. In order to evaluate the possibility to use olive tree-rings for dendrochronology, we examined by various methods the reliability of olive tree-rings identification. Dendrochronological analyses of olive trees growing on the Aegean island Santorini (Greece) show that the determination of the number of tree-rings is impossible because of intra-annual wood density fluctuations, variability in tree-ring boundary structure, and restriction of its cambial activity to shifting sectors of the circumference, causing the tree-ring sequences along radii of the same cross section to differ

Seasonal variations in the stable oxygen isotope ratio of wood cellulose reveal annual rings of trees in a Central Amazon terra firme forest

In Amazonian non-flooded forests with a moderate dry season, many trees do not form anatomically definite annual rings. Alternative indicators of annual rings, such as the oxygen (δ18Owc) and carbon stable isotope ratios of wood cellulose (δ13Cwc), have been proposed; however, their applicability in Amazonian forests remains unclear. We examined seasonal variations in the δ18Owc and δ13Cwc of three common species (Eschweilera coriacea, Iryanthera coriacea, and Protium hebetatum) in Manaus, Brazil (Central Amazon). E. coriacea was also sampled in two other regions to determine the synchronicity of the isotopic signals among different regions. The annual cyclicity of δ18Owc variation was cross-checked by 14C dating. The δ18Owc showed distinct seasonal variations that matched the amplitude observed in the δ18O of precipitation, whereas seasonal δ13Cwc variations were less distinct in most cases. The δ18Owc variation patterns were similar within and between some individual trees in Manaus. However, the δ18Owc patterns of E. coriacea differed by region. The ages of some samples estimated from the δ18Owc cycles were offset from the ages estimated by 14C dating. In the case of E. coriacea, this phenomenon suggested that missing or wedging rings may occur frequently even in well-grown individuals. Successful cross-dating may be facilitated by establishing δ18Owc master chronologies at both seasonal and inter-annual scales for tree species with distinct annual rings in each region