DNA Identification of Lumber
Identifying the species of lumber historically has depended on wood anatomy and can be difficult. Closely related species often cannot be reliably distinguished using wood anatomy alone. Forest Products Laboratory scientists and their collaborators are investigating ways to use DNA to identify lumber species in the field, which would enable industry to better separate closely related species differing in key properties that influence their use.
Southern yellow pine species, such as longleaf pine (Pinus palustris), slash pine (Pinus elliotti), loblolly pine (Pinus taeda), and shortleaf pine (Pinus echinata), can be difficult to distinguish reliably using wood anatomy alone.
Illegally logged, lower-cost imported forest products depress the price of US-produced forest products by an estimated one billion dollars each year by competing with domestically produced forest products. Identifying lumber to species is important to combat this illegal logging, support the US forest products industry, to select wood with improved properties for specialized uses, and to ensure that inferior wood does not enter the U.S. forest products supply chain.
Current methods of identifying lumber rely on wood anatomy—the cellular structure of wood as seen under a microscope—which typically cannot distinguish among species. Plant species are usually defined by flowers, cones, fruits, and leaves, all of which are absent in lumber. While DNA-based methods to identify plant species, typically using leaves, fruits, or seeds as a source of DNA, are highly accurate, wood has much less usable DNA than other plant parts because it often has few living cells from which to extract DNA. Industrial processes involved in forest products such as kiln drying can further degrade DNA in wood as it is converted to lumber or other products.
Forest Products Laboratory scientists and their collaborators have successfully developed a way to identify lumber by extracting DNA from nuclei physically removed from single cells in microscopic slices of wood. Though this method is labor intensive and relies on expensive laboratory equipment and specialized scientific expertise, it has the ability to analyze tiny specimens of wood which were previously impossible to identify with DNA. To overcome these limitations, scientists are also working to develop a field-deployable way to identify and differentiate closely related lumber species with DNA, using simpler techniques that require substantially less scientific expertise, where the size of the wood specimen is not limiting. If successful, this new method could improve lumber identification in real time, which could help reduce the economic impacts of illegal logging and support specialized applications in the forest products industry.
Key Findings
- With the organellar microcapture method, DNA retrieved from wood cell nuclei can be used to identify wood specimens (even trace evidence) with as few as a single intact nucleus
- Scientists are currently working to develop less labor-intensive, field-deployable ways to identify lumber with DNA
Visualization of organellar microcapture in shagbark hickory (Carya ovata) under transmitted light (A, C) and fluorescence microscopy (B, D). A An empty micropipette prior to insertion into the target parenchyma cell. B The same frame as A, with the DAPI-stained target nucleus (arrow) easily discernible, and the parenchyma cell walls exhibiting lignin autofluorescence. C Amyloplasts and the target nucleus successfully aspirated into the micropipette. D The same frame as C, confirming that the nucleus is among the captured organelles.
Most cells in wood are dead at maturity, even in the living tree in the forest, which means that they lack intact organelles (e.g., nuclei, mitochondria, chloroplasts) from which to extract DNA for identification. While laboratory protocols can be modified to successfully amplify DNA, these modified protocols often require relatively large amounts of wood to recover small amounts of DNA.
Forest Products Laboratory scientists and collaborators recently developed a successful method to extract DNA from individual wood cells. This method removes nuclei from parenchyma cells, which are one of the few types of wood cells that still have organelles. Scientists tested this method in both hardwoods (hickory and basswood) and softwoods (spruce) and confirmed that they could extract DNA and identify the species from these nuclei. They also successfully extracted DNA from aged wood samples that were over 60 years old.
Although this method is successful, it is labor intensive. The microcapture process involves staining sections about 15 to 25 micrometers in thickness, using transmitted light and fluorescence microscopy to visualize the nuclei, and then using a micromanipulator (i.e., a specialized tool used to make tiny, precise movements) and micropipettes to physically extract the nuclei from the cells. The nuclei are then transferred to a small plastic tube filled with a lysis buffer to extract DNA, after which they undergo a polymerase chain reaction (PCR) protocol to make many copies of the DNA to be sequenced.
Key Findings
- By extracting DNA from individual wood parenchyma cells, the organellar microcapture method enables wood species identification using DNA, even in forensically small trace evidence specimens previously too small for analysis
- The microcapture method can be used to extract DNA from both hardwoods and softwoods, can work with samples aged over 60 years, and is probably effective for any specimen with microscopically intact organelles
- Despite the effectiveness of this technique, it can be labor intensive and requires highly specialized expertise and equipment in a laboratory setting.
Equipment for extracting DNA in the field is small and portable.
The microcapture method to extract DNA and identify lumber species works, but it is expensive and labor intensive. Currently, scientists at the Forest Products Laboratory are collaborating to develop a field-deployable method to extract DNA for species identification.
When successful, this method will enable species claim verification (i.e., the ability to claim that lumber is truly a certain species) among related species with distinct properties. For example, southern pines, which include longleaf pine (Pinus palustris), slash pine (Pinus elliottii), loblolly pine (Pinus taeda), and shortleaf pine (Pinus echinata) have wood that is impossible to distinguish by wood anatomy alone. Longleaf and slash pine may be preferred due to higher specific gravity and better strength properties. Distinguishing among these species could benefit sawmills and lumber traders who work with machine stress rated lumber and could support timber inspectors, chain of custody investigation, and product claim verification efforts. The availability of this technique is intended to result in improved profits and competitiveness for industry and more efficient use of domestic forest resources.
People
-
Person
Alex C. Wiedenhoeft, PhD
Research Botanist and Team Leaderhttps://research.fs.usda.gov/about/people/alex.c.wiedenhoeft -
Person
Grant T. Kirker, PhD
Research Forest Products Technologisthttps://research.fs.usda.gov/about/people/grant.kirker -
Person
Amy B. Bishell
Biological Science Technicianhttps://research.fs.usda.gov/about/people/amy.b.bishell
Collaborators
Adriana Costa, Mississippi State University
Miftah Rahman, Mississippi State University