Tree sleuths are using DNA tests and machine vision to crack timber crimes
05.04.2019
Tree sleuths are using DNA tests and machine vision to crack timber crimes. Scientists are optimistic that innovative techniques can pinpoint the true origin of timber.
To prove the origin of the rosewood, Sri Lankan authorities sent samples to a laboratory in Oregon that was testing a new weapon in the fight against illegal logging — a US$200,000 mass spectrometer. In mere seconds, scientists at the US Fish and Wildlife Service Forensics Lab in Ashland determined that the wood bore the distinct chemical signature of a Madagascan species of rosewood — and not one of wood legal to export.
After a drop in the early 2000s, the trade in illegally logged timber is rising again. Interpol estimates that between 15% and 30% of the global timber trade violates either national law or international treaty. In some tropical countries, such as the Democratic Republic of the Congo, Laos and Papua New Guinea, illegal timber could account for more than 70% of the nation’s production. This market is worth between $10 billion and $100 billion a year, according to a 2016 report from the International Union of Forest Research Organizations in Vienna.
Some high-income countries — including the United States, South Korea and those in the European Union — have banned the import of illegally sourced wood and products made from it, and forced importers to prove their supplies are bona fide. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), an international agreement signed by 183 countries, forbids or restricts trade in the most threatened species. In 2016, it added to the list all the rosewoods belonging to the genus Dalbergia.
Such efforts suggest that illegal timber imports are thriving — in part because the crime is so difficult to uncover. From Brazil and Madagascar to Europe’s Carpathian Mountains, trees move from forest to living room through serpentine routes, with twists and turns where illegal wood can be hidden. A single piece of plywood can contain 18 different tropical timbers. An illegally harvested oak tree from Russia can voyage to Vietnam to become a table, and by the time it reaches a US retailer, its origin has mysteriously changed.
The global paper trail that accompanies timber is notoriously easy to manipulate. So those tasked with fighting illegal trade — and the companies now compelled to crack down on it — are turning to technologies that can spot the signatures of illicit timber. Scientists are developing a suite of tools that can identify the species and the country, and even the region, it came from. Thanks to advances in chemical and genetic fingerprinting, it is now possible to determine where a tree grew — sometimes down to a particular patch of forest. Some of these tools are already being used to catch criminals.
A few formidable obstacles are keeping these techniques out of routine use, one of the biggest of which is a lack of reference samples against which to compare suspect timber. But there are signs of progress towards developing a library of the world’s forests. In February, the US government and various international partners said that they would plough resources into collecting and curating thousands of georeferenced tree samples.
“I’m convinced that in five, ten years — with any wood product — you’ll be able to know exactly where it came from,” says Phil Guillery, head of supply-chain integrity at the Forest Stewardship Council (FSC), a voluntary certification body in Bonn, Germany, and one of the forces behind the library effort. “You can’t fake the science.”
Anatomy of a crime
A giant eucalyptus tree dominates the view from Peter Gasson’s office in London’s Royal Botanic Gardens, Kew. The lab of the wood anatomist is strewn with curiosities: ‘oak’ blinds that turned out to be softwood and a millefeuille of plywood from China with a suspicious veneer. In a cabinet are 36,000 microscope slides, each containing a sliver from Kew’s vast collection of wood samples. The microscope picks out more than 100 features that betray the sample’s identity. 
Two kinds of wood lie beneath a tree’s bark. An outer sapwood layer holds vessels called xylem tubes that siphon water and minerals up the plant. In the inner layer, of heartwood, resin blocks much of the xylem. A horizontal section of the wood reveals the rings; a vertical section exposes the long lines of vessel elements, giving the familiar grain of the wood. Depending on the genus, vessels can lie in neat, concentric rings or can be dispersed through the trunk.
Gasson’s lab has hundreds of obscure guides to wood anatomy, “but mostly it’s all in here”, he says, pointing to his head. It’s taken 30 years to understand the quirks of the world’s 30,000 or so tree species, so that knowledge is precious. But, after staff cuts, Gasson is Kew’s sole wood anatomist, and one of just 131 members of the International Association of Wood Anatomists.
Yet wood anatomists are more in demand than ever. “Now, is as sexy as being a wood anatomist will ever be,” says Alex Wiedenhoeft, Gasson’s counterpart at the US Forest Products Laboratory in Madison, Wisconsin.
Gerald Koch at the Thünen Centre of Competence on the Origin of Timber in Hamburg, Germany, has helped to push wood anatomy to new heights, using it to expose a far-reaching scandal involving European charcoal supplies. In 2017, the wildlife charity WWF in Germany approached Koch over concerns that Germans were unwittingly using charcoal that had been made from protected forest wood.
Charcoal is too brittle to slice into the thin sections that wood anatomists ordinarily analyse under a microscope — “If you cut it with a knife, you just get a powder,” Koch says. So his team worked out a way to digitally reconstruct such sections from irregular lumps of charcoal, using an €80,000 (US$90,500) 3D reflected-light microscope — the first application of the technology to wood anatomy.
Koch’s analysis provided enough information for Johannes Zahnen, a specialist in forest policy at WWF Germany, to deduce that 40% of the samples of barbecue charcoal he had submitted to Koch had come from tropical countries.
Microscopic details of charcoal can help researchers to determine the type of wood it’s from. “That was a surprise to everybody,” says Zahnen. Armed with this and other questionable claims of provenance exposed by Koch, he traced a large proportion of Germany’s charcoal back to Paraguay and Nigeria, two countries where illegal logging is rife. The investigation triggered others in Europe and, ultimately, helped to expose a major logging fraud in Ukraine.
The dearth of wood anatomists has inspired some to turn to machines. At the Forest Products Laboratory, Wiedenhoeft and engineer John Hermanson have invented the XyloTron, which they hope will be used as a field screening tool that can alert inspectors to timbers that merit further, forensic analysis. The machine, which is currently in field trials, consists of a customized camera and a computer loaded with a reference collection of images that allow the device to identify wood types.