Verifying the declared origin of timber using stable isotope ratio and multi-element analyses

The FLEGT (Forest Law Enforcement Governance and Trade) regulations were introduced in 2003 with the intention of reversing the rate of destruction of the world’s forests. One of the European Union’s aims is to halt the import of illegally acquired and endangered timber. The timber trade law (regulation (EU) 995/2010) stipulates that importers of tropical timber must be able to identify the origin of timber used in their products, and from the 3rd March 2013, it is a criminal offence to sell endangered timber in the European Union without a FLEGT licence. There are few analytical methods available to determine the declared origin of timber. The current procedure involves checking of shipping documents and visual checks of common timber species for origin identification. In this project, one hundred timber core samples of Sapele (Entandrophragma), Rosewood (Dalbergia) and Ebony (Diospyros) trees were taken from across West Africa and Madagascar. The δ2H, δ13C, and δ18O isotopes of the extracted cellulose were determined by using an elemental analyser coupled to an isotope ratio mass spectrometer (EA-IRMS). The study revealed that δ2H and δ18O of cellulose showed no correlation with δ2H and δ18O of precipitation water, suggesting the leaf-to-air-vapour pressure difference (VPD), as well as alternative ground water sources may influence the isotopes laid down in cellulose of tropical timber. Additionally, multi-element profiles of the timber samples were determined by inductively coupled plasma mass spectrometry (ICP-MS), to assess the potential for geographical origin discrimination based on the combined profile of stable isotope ratios and multi-element concentrations. Using the multivariate statistical technique of canonical discriminant analysis (CDA), data were processed enabling a cross validation rate of 86.6%. Twelve elemental variables were selected by the CDA for the multivariate analysis (Mo, Zn, Ca, As, δ13C, δ18O, Sb, Mn, Pb, Cu, La, Ba), which provided maximum discrimination between the timber samples originating from Ghana, Cameroon, The Congo, The Democratic Republic of Congo (DRC), and Madagascar. Hence, the combination of the methodologies of stable isotope ratio and trace element analysis offers an effective approach to verifying the declared origin of timber.