New technique in forensic fingerprinting could tackle illegal logging

Eradicating illegal logging is especially difficult since it is often not possible to identify a wood’s original source.

Now, Oregon-based scientists have developed a technique that uses the chemical make-up of a wood sample to pinpoint its origin to a smaller area than ever before.

Endangered species or populations of trees are protected by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the U.S. Lacey Act, which require that imported wood is accompanied by documents that state its species and geographic origin. Unfortunately, these papers are often forged or inaccurate, so a rapid and accurate method of identifying imported wood is critical for law enforcement.

Under a microscope, wood from a particular species has distinguishing characteristics, but it is almost impossible to tell where it came from. This is a problem for species in which only certain populations are protected, such as those in specific countries or large preserves. To tackle this issue, a group of researchers led by

By applying chemical fingerprinting techniques to analyse the molecules in the annual growth rings of Douglas-fir trees (Pseudotsuga menziesii), researchers could successfully distinguish wood from two separate populations of this widespread and economically important species. The study, led by Dr Richard Cronn of the Pacific Northwest Research Station, USDA Forest Service, used a technique called DART-TOFMS (direct analysis in real time time-of-flight mass spectrometry) to measure chemical presence and abundance of Douglas-fir trees from two mountain ranges, the neighbouring Oregon Coast and Cascade ranges. The chemical screening only requires a tiny sample of wood, which can be prepared for analysis in just 15 seconds.

By comparing the molecular differences of 188 trees, Cronn and his team could tell which region a particular tree came from with a 70-76% accuracy. The technique was previously used to distinguish the wood of closely related species, or populations of the same species from different countries, but this is the first time that DART-TOFMS has been used to identify the source of samples over such small distances (under 100 km).

“Douglas-fir may be the most important structural timber tree in North America, but we still have much to learn about its wood chemistry,” Cronn said.

Their study is published in a recent issue of Applications in Plant Sciences.

In timber production, the older, darker heartwood in the centre of the tree trunk is particularly valuable, and it was this wood that was investigated in the study. The team analysed the three oldest annual growth rings shared between all of the samples, which grew in 1986 to 1988. While they did not find any conclusive differences between the three years, it is possible that extreme weather events could lead to more dramatic differences between the chemical fingerprints of some annual rings, and the authors conclude that more extensive sampling is required.

Cronn hopes that this work on Douglas-fir will be used to protect a wider range of trees in the future: “We hope the wood forensics community will take what we learn from this regionally abundant tree and apply it to hardwood and softwood species that are the targets of illegal logging and the focus of conservation efforts.”