Tracing the origin of wood at the regional scale with dendrochemical markers: elemental and strontium and neodymium isotopic composition.

The dendrochemical approach holds significant promise for determining the geographical origin of wood as a complementary tool to dendroprovenancing based on tree-ring width. Tracing the origin of wood based on its elemental and isotopic composition is in particular interesting for provenance studies at the regional scale, as dendrochemical signatures are indicative of geological and pedological characteristics. Although, absorption of nutrients and trace elements reflects the composition of soil bioavailable pools, it is also modulated by multiple environmental and tree related factors. We assess the dendrochemical approach in oak wood provenance studies regarding the challenges posed by 1) geochemical variation at a local level, and 2) dendrochemical variation related to oak species, age and social status. A combination of 13 elemental concentrations and 2 isotope - Sr and Nd - ratios was analyzed in oak wood from 12 forests situated in the large Seine river catchment in France. The sampling targeted sites with representative types of geological parent material, where adult trees of two common temperate Quercus species (Quercus petraea and Quercus robur) were selected. The impact of tree characteristics was markedly weaker than that of the site factor and the minimal differences in dendrochemical composition between Quercus petraea and Quercus robur were considered without effect on determination of the geographical origin. Linear discriminant analysis based on Ca-normalized elemental concentrations and Sr and Nd isotope ratios correctly classified the origin of 93 % of the sampled trees. Strontium isotope ratio ⁸⁷Sr/⁸⁶Sr was the strongest provenance indicator capable of determining the origin of 55 % of wood samples on its own. Our system based on elemental and strontium and neodymium isotopic compositions provides robust indicators for wood tracing and might be applied to provenance studies in environment, physiology, history and archeology.