Background
Stable isotope ratios in the wood have long been a primary focus point for origin determination of timber. This is because it is a well established method that has been applied to various other commodities like beef, eggs or cacao. As for other commodities, geographical variation in the wood isotopic composition is caused by differences in climate, geology and/or atmospheric deposition. As a result, the isotopic composition reflects the area where the tree was growing.
However, results vary across locations and scales. While stable isotopes have shown promising differences in some locations for example in Gabon, so far we found insufficient variation for origin verification neighboring Cameroon.
Stable isotope measurements
We have experience in measuring several stable isotope ratios in wood:
- Sulphur, δ34S
- Hydrogen, δ2H
- Oxygen, δ18O
- Carbon δ13C
For the analyses we take a subsample of heartwood in the radial direction including at least 3–5 cm to include wood formed during multiple years. In this way we preserve a more stable signal that is less affected by year-to-year variation. All our δ13C, δ18O and δ2H stable isotope measurements are based on cellulose, which means we do cellulose extractions first. In this way we increase purity of the samples an make ratios more comparable among timber species. δ34S we measure in powderized whole wood, because Sulphur concentrations cannot be measured in cellulose.